COLOR SCANHEAD AND CURRENCY HANDLING SYSTEM EMPLOYING THE SAME

Abstract: A document handling system (10) is configured for processing a variety of different documents. The system includes an input receptacle (36) for receiving a stack of documents, a standard sensor (70) for scanning at least one non-color characteristic of the documents in the stack, a color sensor (300) for scanning the color characteristics of the documents, and an output receptacle (117) for receiving the documents after they have been processed. A transport mechanism (123, 141) is included for transporting the documents, one at a time, from the input receptacle (36) past the sensors (70, 300) to the output receptacle (117). An operator interface is provided for displaying information to an operator and inputting information into the system. A processor is also included for processing the data gathered from the sensors (70, 300) to evaluate the documents.

Description: 1 COLOR SCANHEAD AND CURRENCY HANDLING SYSTEM EMPLOYING THE SAME FIELD OF THE INVENTION The present invention relates generally to currency handling systems such as those capable of distinguishing or discriminating between currency bills of different denominations and, more particularly, to such systems that employ color sensors. BACKGROUND OF THE INVENTION Systems that are currently available for simultaneous scanning and counting of documents such as paper currency are relatively complex and costly, and relatively large in size. The complexity of such systems can also lead to excessive service and maintenance requirements. These drawbacks have inhibited more widespread use of such systems, particularly in banks and other financial institutions where space is limited in areas where the systems are most needed, such as teller areas. The above drawbacks are particularly difficult to overcome in systems which offer much-needed features such as the ability to authenticate the genuineness and/or determine the denomination ofthe bills. Therefore, there is a need for a small, compact system that can denominate bills of different denominations of bills. Likewise there is such a need for a system that can discriminate the denominations of bills from more than more country. Likewise there is a need for such a small compact system that can readily be made to process the bills from a set of countries and yet has the flexibility so it can also be readily made to process the bills from a different set of one or more countries. Likewise, there is a need for a currency handling system that can satisfy these needs while at the same time being relatively inexpensive. There is also a need for a currency handling system that can retrieve color information from currency bills. Currently, there are a systems that do perform color analysis on bills; however, these systems suffer from one or more drawbacks. For example, many of these color-capable systems are extremely large and expensive. Furthermore, some of these systems employ a color CCD array to scan bills. Color CCD arrays have the disadvantages of being expensive and requiring a considerable amount of processing power, thus requiring more expensive signal processors and more processing 2 time. Additionally, one problem associated with color scanning is a need for bills to be more brightly illuminated than for standard scanning or analysis. However, adding additional light sources adds to the cost ofthe system and undesirably increases the heat that is generated and the power that is consumed. Another drawback of prior color-capable currency handling systems is that they employ color scanhead arrangements that are themselves large in size which in turn requires the systems in which they are used to be larger. Accordingly, there is a need for a small, compact, and less expensive full color scanning currency handling system. A full color scanning currency handling system uses all three ofthe primary colors to process and discriminate a currency bill or document. The term "primary colors" as used herein means colors from which all colors may be generated and includes the three additive primary colors (red, green, and blue) as well as the three subtractive primary colors (magenta, yellow, and cyan). Likewise, there is a need for a full color scanhead arrangement for use in such a system that will require less processing power and adequately address the issues of providing enough illumination while at the same time avoiding the problems of excessive heat generation and power consumption. There is a need for a full color scanning arrangement that can meet these needs in a cost effective manner. There is also a need for a system that can distinguish documents via color. There is a further need for a system that can quickly preselect master patterns. Likewise there is a need for a system that can limit the master patterns compared to the test bill pattern thus reducing the number of no-calls and/or mis-calls. There is also a need for a system that allows high speed, low cost scanning of a wide variety of money and documents including casino script, amusement park script, stock certificates, bonds, postage stamps, and/or food coupons, or other such documents. Finally, there is a need for a system that can provide not only black and white data, but also color data corresponding to the document being processed. SUMMARY OF THE INVENTION In accordance with one aspect ofthe present invention, there is provided a currency scanning system that uses full color scanning to discriminate and/or ~> authenticate a variety of different currencies, including different denominations within a currency set. In accordance with another aspect of this invention, there is provided such a currency scanning system utilizing color sensors that eliminate the need for lenses to focus light, thus reducing the cost and size ofthe system. In one embodiment, the system ofthe invention automatically learns the characteristics of authentic currency from a variety of different currency systems. In accordance with another aspect of this invention, there is provided a document handling system for processing documents, the system comprising a first sensor for scanning at least one characteristic of a document other than color, a full color sensor for scanning color characteristics ofthe document, and a processor for processing data corresponding to the characteristics scanned from one or more documents with the first sensor and the color sensor and for using the data to evaluate one or more document. In accordance with another aspect of this invention, there is provided a document scanning system comprising a first scanhead assembly for scanning a first side of a document, said first scanhead assembly including at least one optical sensor for scanning optical characteristics of a document and size sensors comprising a pair of laterally spaced apart linear optical arrays extending a predetermined distance oppositely laterally outwardly for detecting opposite side edges of a document, for determining the length of a document in a direction transverse to a path of travel of a document past said scanhead. In accordance with another aspect of this invention, there is provided a document handling method for processing documents, the method comprising the steps of scanning at least one characteristic of a document other than color, scanning full color characteristics ofthe document, processing data corresponding to the color and other characteristics scanned from one or more documents, and using the data to evaluate one or more documents. In accordance with another aspect of this invention, there is provided a color scanhead apparatus for a document handling system, said color scanhead comprising a full color sensor including a plurality of color cells, each cell comprising a primary color sensor for sensing each of at least two primary colors. 4 In accordance with another aspect of this invention, there is provided a color scanning method for a document handling system for processing documents, the method comprising the steps of scanning full color characteristics of a document, processing data corresponding to the characteristics scanned from one or more documents, and using the data to evaluate one or more documents. These and other features are provided by a system for processing a variety of different currencies. The system includes an input receptacle for receiving a stack of currency bills to be counted, a standard sensor for scanning the black and white characteristics of the bills in the stack, a color sensor for scanning the color characteristics of the bills, and an output receptacle for receiving the bills after they have been processed. A transport mechanism is included for transporting bills, one at a time, from the input receptacle past the sensors to the output receptacle. An operator interface is provided for displaying information to an operator and inputting information to the system. A processor is also included for processing the data gathered from the sensors to evaluate the bills. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a functional block diagram of a currency handling system embodying the present invention; FIG. 2a is a perspective view of a single pocket currency handling system according to one embodiment ofthe present invention; FIG. 2b is a sectional side view ofthe single pocket currency handling system of FIG. 2a depicting various transport rolls in side elevation; FIG. 2c is a top plan view ofthe interior mechanism ofthe system of FIG. 2a for transporting bills across a scanhead, and also showing the stacking wheels at the front of the system; FIG. 2d is a sectional top view ofthe interior mechanism ofthe system of FIG. 2a for transporting bills across a scanhead, and also showing the stacking wheels at the front ofthe system; 5 FIG. 3a is a perspective view of a two-pocket currency handling system according to one embodiment ofthe present invention; FIG. 3b is a sectional side view ofthe two-pocket currency handling system of FIG. 3 a depicting various transport rolls in side elevation; FIG. 4a is a sectional side view of a three-pocket currency handling system depicting various transport rolls in side elevation; FIG. 4b is a sectional side view of a four-pocket currency handling system depicting various transport rolls in side elevation; FIG. 4c is a sectional side view of a six-pocket currency handling system depicting various transport rolls in side elevation; FIG. 5a is an enlarged sectional side view depicting the scanning region according to one embodiment ofthe present invention; FIG. 5b is a sectional side view depicting the scanheads according to one embodiment ofthe present invention; FIG. 5c is a front view depicting the scanheads of FIG. 5b according to one embodiment ofthe present invention; FIG. 6a is a perspective view of a color scanhead module; FIG. 6b is an exploded perspective view ofthe color scanhead module of FIG. 6a; FIG. 6c is a top view ofthe color scanhead module of FIG. 6a; FIG. 6d is a front view ofthe color scanhead module of FIG. 6a; FIG. 6e is a side view ofthe color scanhead module of FIG. 6a; FIG. 6f is an end view of a color scanhead; FIG. 6g is a side view ofthe color scanhead module of FIG. 6a including the color scanhead of FIG. 6f; FIG. 7 is a functional block diagram of a standard optical scanhead; FIG. 8 is a functional block diagram of a full color scanhead; FIG. 9a is a perspective view of a U.S. currency bill and an area to be optically scanned on the bill; FIG. 9b is a diagrammatic perspective illustration ofthe successive areas scanned during the traversing movement of a single bill across an optical scanhead according to one embodiment ofthe present invention; 6 FIG. 9c is a diagrammatic side elevation view ofthe scan area to be optically scanned on a bill according to one embodiment ofthe present invention; FIG. 9d is a top plan view of a bill indicating a plurality areas to be optically scanned on the bill; FIG. 10a is a perspective view of a bill and a plurality areas to be color scanned on the bill; FIG. 10b is a diagrammatic perspective illustration ofthe successive areas scanned during the traversing movement of a single bill across a color scanhead according to one embodiment ofthe present invention; FIG. 10c is a diagrammatic side elevation view ofthe scan area to be color scanned on a bill according to one embodiment ofthe present invention; FIG. 11 is a timing diagram illustrating the operation ofthe sensors sampling data according to an embodiment ofthe present invention; FIG. 12a-12e are graphs of color information obtained by the color scanhead in FIG. 13; FIG. 13a is a top perspective view of one embodiment of a color scanhead for use in the currency handling systems of FIGS. 1-4; FIG. 13b is a bottom perspective view ofthe color scanhead of FIG. 13a; FIG. 13c is a bottom view ofthe color scanhead of FIG. 13a; FIG. 13d is a sectional side view ofthe color scanhead of FIG. 13c; FIG. 13e is an enlarged bottom view of a section ofthe color scanhead of FIG. 13b; FIG. 13f is a sectional end view ofthe color scanhead of FIG. 13a; FIG. 13g is an illustration ofthe light trapping geometry ofthe manifold ofthe scanhead of FIG. 13a; FIG. 14 is a functional block diagram of a magnetic scanhead; FIG. 15a is a top view ofthe standard scanhead of FIG. 5a (with size detector element); FIG. 15b is a bottom view ofthe standard scanhead of FIGS. 5a and 15a (with size detector element); 7 FIG. 16 is a block diagram of a size detection circuit for measuring the long (or "X") dimension of a bill; FIG. 17 is a block diagram of a digital size detection system for measuring the narrow (or "Y") dimension of a bill; FIG. 18 is a timing diagram illustrating the operation ofthe size detection method of FIG. 17; FIG. 19 is a block diagram of an analog size detection system for measuring the narrow (or "Y") dimension of a bill; FIG. 20 is a functional block diagram of a fold/hole detection system; FIG. 21 is a flow chart of one embodiment ofthe learn mode; FIG. 22 is a flow chart further defining a step ofthe flow chart of FIG. 21; FIGS. 23a-d are a flow chart of one embodiment of how the system operates in standard bill evaluation mode; and FIGS. 24a-h are flow charts of another embodiment ofthe color correlation scheme shown in FIGS. 23 c-d. While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope ofthe invention as defined by the appended claims. DETAILED DESCRIPTION OF THE EMBODIMENTS FIG. 1 illustrates in functional block diagram form the operation of currency handling systems according to the present invention. FIGS. 2a-2d, 3a-3b, and 4a-4c then illustrate various physical embodiments of currency handling systems that function as discussed in connection with FIG. 1 and that employ a color scanning arrangement according to the present invention. These embodiments will be described first and then the details concerning embodiments of color scanheads and processing will be described. Turning to FIG. 1, a currency handling system 10 comprises an input receptacle 36 for receiving a stack of currency bills to be processed. The processing may include evaluating, denominating, authenticating, and/or counting the currency bills. In addition 8 to handling currency bills, the currency handling system 10 may be designed to accept and process other documents including but not limited to stamps, stock certificates, coupons, tickets, checks and other identifiable documents. Bills placed in the input receptacle are transported one by one by a transport mechanism 38 along a transport path past one or more scanheads or sensors 70. The scanhead(s) 70 may perform magnetic, optical and other types of sensing to generate signals that correspond to characteristic information received from a bill 44. In embodiments to be described below, the scanhead(s) 70 comprises a color scanhead. In the embodiment shown in FIG. 1, the scanhead(s) 70 employs a substantially rectangularly shaped sample region 48 to scan a segment of each passing currency bill 44. After passing the scanhead(s) 70, each ofthe bills 44 is transported to one or more output receptacles 34 which may include stacking mechanisms to re-stack the bills 44. According to some embodiments the scanhead(s) 70 generates analog output(s) which are amplified by an amplifier 58 and converted into a digital signal by means of an analog-to-digital converter (ADC) unit 52 whose output is fed as a digital input to a controller or processor such as a central processing unit (CPU), a processor or the like. The process (such as a microprocessor) controls the overall operation ofthe currency handling system 10. An encoder 14 linked to the bill transport mechanism 38 provides input to the PROCESSOR 54 to determine the timing ofthe operations ofthe currency handling system 10. In this manner, the processor is able to monitor the precise location of bills as they are transported through the currency handling system. The PROCESSOR 54 is also operatively coupled to an internal or an external memory 56. The memory comprises one or more types of memories such as a random access memory ("RAM"), a read only memory ("ROM"), EPROM or flash memory depending on the information stored or to be stored therein. The memory 56 stores software codes and/or data related to the operation ofthe currency handling system 10 and information for denominating and/or authenticating bills. An operator interface panel and display 32 provides an operator the capability of sending input data to, or receiving output data from, the currency handling system 10. Input data may comprise, for example, user-selected operating modes and user-defined operating parameters for the currency handling system 10. Output data may comprise, 9 for example, a display ofthe operating modes and/or status ofthe currency handling system 10 and the number or cumulative value of evaluated bills. In one embodiment, the operator interface panel 32 comprises a touch-screen "keypad" and display which may be used to provide input data and display output data related to operation ofthe currency handling system 10. Alternatively, the operator interface 32 may employ physical keys or buttons and a separate display or a combination of physical keys and displayed touch-screen keys. A determination of authenticity or denomination of a bill under test is based on a comparison of scanned data associated with the test bill to the corresponding master data stored in the memory 56. For example, where the currency handling system 10 comprises a denomination discriminator, a stack of bills having undetermined denominations may be processed and the denomination of each bill in the stack determined by comparing data generated from each bill to prestored master information. If the data from the bill under test sufficiently matches master information associated with a particular denomination and bill-type stored in memory, a determination of denomination may be made. The master information may comprise numerical data associated with various denominations of currency bills. The numerical data may comprise, for example, thresholds of acceptability to be used in evaluating test bills, based on expected numerical values associated with the currency or a range of numerical values defining upper and lower limits of acceptability. The thresholds may be associated with various sensitivity levels. The master information may also comprise pattern information associated with the currency such as, for example, optical or magnetic patterns. Turning to FIGS. 2a-2d, FIG. 2a is a perspective view of a currency handling system 10 having a single output receptacle 117 according to one embodiment ofthe present invention. FIG. 2b is a sectional side view ofthe single pocket currency handling system of FIG. 2a depicting various transport rolls in side elevation and FIG. 2c is a top plan view ofthe interior mechanism ofthe system of FIG. 2a for transporting bills across a scanhead, and also showing the stacking wheels 112, 113 at the front ofthe system. The mechanics of this embodiment will be described briefly below. For more detail, single pocket currency handling systems are described in greater detail in U.S. Patent No. 10 5,687,963 entitled "Method and Apparatus for Discriminating and Counting Documents," and U.S. Patent No. 5,295,196 entitled "Method and Apparatus for Currency Discriminating and Counting," both of which are assigned to the assignee of the present invention and incorporated herein by reference in their entirety. The physical embodiment ofthe currency handling system described in U.S. Patent No. 5,687,963 including the transport mechanism and its operation is similar to that depicted in FIGS. 2a-2d except for the scanhead arrangement. The currency handling system of FIGS. 2a- 2d employs a color scanhead 300 (FIG. 2b) according to the present invention or in addition to one ofthe standard scanheads 70 described in U.S. Patent No. 5,687,963. The currency handling system of FIGS. 2a-2d is designed to transport and process bills at a rate in excess of 800 bills per minute, preferably in excess of . 1200 bills per minute. In the single-pocket system 10, the currency bills are fed, one by one, from a stack of currency bills placed in the input receptacle 36 into a transport mechanism, which guides the currency bills past sensors to a single output receptacle 117. The single-pocket currency handling system 10 includes a housing 100 having a rigid frame formed by a pair of side plates 101 and 102, top plate 103a, and a lower front plate 104. The currency handling system 10 also has an operator interface 32a. As shown in FIG. 2a the operator interface panel comprises a LCD display and physical keys or buttons. Alternatively or additionally, the operator interface panel may comprise a touch screen such as a full graphics display. The input receptacle 36 for receiving a stack of bills to be processed is formed by downwardly sloping and converging walls 105 and 106 formed by a pair of removable covers 107 and 108. The rear wall 106 supports a removable hopper (extension) 109 which includes a pair of vertically disposed side walls 110a and 110b which complete the receptacle for the stack of currency bills to be processed. From the input receptacle, the currency bills are moved in seriatim from the bottom ofthe stack along a curved guideway 111 which receives bills moving downwardly and rearwardly and changes the direction of travel to a forward direction. The curvature ofthe guideway 111 corresponds substantially to the curved periphery of a drive roll 123 so as to form a narrow passageway for the bills along the rear side ofthe drive roll. The exit end ofthe guideway 111 directs the bills onto a linear path where the 11 bills are scanned and stacked. The bills are transported and stacked with the narrow dimension ofthe bills maintained parallel to the transport path and the direction of movement at all times. Stacking ofthe bills is effected at the forward end ofthe linear path, where the bills are fed into a pair of driven stacking wheels 112 and 113. These wheels project upwardly through a pair of openings in a stacker plate 114 to receive the bills as they are advanced across the downwardly sloping upper surface ofthe plate. The stacker wheels 112 and 113 are supported for rotational movement about a shaft 115 journalled on the rigid frame and driven by a motor 116. The flexible blades ofthe stacker wheels deliver the bills into the output receptacle 117 at the forward end ofthe stacker plate 114. During operation, a currency bill which is delivered to the stacker plate 114 is picked up by the flexible blades and becomes lodged between a pair of adjacent blades which, in combination, define a curved enclosure which decelerates a bill entering therein and serves as a means for supporting and transferring the bill into the output receptacle 117 as the stacker wheels 112, 113 rotate. The mechanical configuration ofthe stacker wheels, as well as the manner in which they cooperate with the stacker plate, is conventional and, accordingly, is not described in detail herein. Returning now to the input region ofthe system as shown in FIGS. 2a-2d, 5a-b, and 6a, bills that are stacked on the bottom wall 105 ofthe input receptacle are stripped, one at a time, from the bottom ofthe stack.. The lowermost bill is picked by a pair of auxiliary feed wheels 120 mounted on a drive shaft 121 which, in turn, is supported across the side walls 101, 102. The auxiliary feed wheels 120 project through a pair of slots formed in the cover 107. Part ofthe periphery of each wheel 120 is provided with a raised high-friction, serrated surface 122 which engages the bottom bill ofthe input stack as the wheels 120 rotate, to initiate feeding movement ofthe bottom bill from the stack.. The serrated surfaces 122 project radially beyond the rest of each wheel's periphery so that the wheels "jog" the bill stack during each revolution so as to agitate and loosen the bottom currency bill within the stack, thereby facilitating the stripping ofthe bottom bill from the stack. The auxiliary feed wheels 120 feed each stripped bill onto a drive roll 123 mounted on a driven shaft 124 supported across the side walls 101 and 102. The drive 12 roll 123 includes a central smooth friction surface 125 formed of a material such as rubber or hard plastic. This smooth friction surface 125 is sandwiched between a pair of grooved surfaces 126 and 127 having serrated portions 128 and 129 formed from a high- friction material. This feed and drive arrangement is described in detail in U.S. Patent No. 5,687,963. In order to ensure firm engagement between the drive roll 123 and the currency bill being fed, an idler roll 130 urges each incoming bill against the smooth central surface 125 ofthe drive roll 123. The idler roll 130 is journalled on a pair of arms which are pivotally mounted on a support shaft 132. Also mounted on the shaft 132, on opposite sides ofthe idler roll 130, are a pair of grooved stripping wheels 133 and 134. The grooves in these two wheels 133, 134 are registered with the central ribs in the two grooved surfaces 126, 127 ofthe drive roll 123. The wheels 133, 134 are locked to the shaft 132, which in turn is locked against movement in the direction ofthe bill movement (counterclockwise for roll 123, clockwise for wheels 133, 134, as viewed in FIG. 2b) by a one-way clutch (not shown). Each time a bill is fed into the nip between the guide wheels 133, 134 and the drive roll 123, the clutch is energized to turn the shaft 132 just a few degrees in a direction opposite the direction of bill movement. These repeated incremental movements distribute the wear uniformly around the circumferences ofthe guide wheels 133, 134. Although the idler roll 130 and the guide wheels 133, 134 are mounted behind the guideway 111, the guideway is apertured to allow the roll 130 and the wheels 133, 134 to engage the bills on the front side ofthe guideway. Beneath the idler roll 130, a spring-loaded pressure roll 136 (FIG. 2b) presses the bills into firm engagement with the smooth friction surface 125 ofthe drive roll as the bills curve downwardly along the guideway 111. This pressure roll 136 is journalled on a pair of arms 137 pivoted on a stationary shaft 138. A spring 139 attached to the lower ends ofthe arms 137 urges the roll 136 against the drive roll 133, through an aperture in the curved guideway 111. At the lower end ofthe curved guideway 111, the bill being transported by the drive roll 123 engages a flat transport or guide plate 140. Currency bills are positively driven along the flat plate 140 by means of a transport roll arrangement which includes the drive roll 123 at one end ofthe plate and a smaller driven roll 141 at the other end of 13 the plate. Both the driver roll 123 and the smaller roll 141 include pairs of smooth raised cylindrical surfaces 142 and 143 which hold the bill flat against the plate 140. A pair of O-rings fit into grooves 144 and 145 formed in both the roll 141 and the roll 123 to engage the bill continuously between the two rolls 123 and 141 to transport the bill while helping to hold the bill flat against the transport plate 140. The flat transport or guide plate 140 is provided with openings through which the raised surfaces 142 and 143 of both the drive roll 123 and the smaller driven roll 141 are subjected to counter-rotating contact with corresponding pairs of passive transport rolls 150 and 151 having high-friction rubber surfaces. The passive rolls 150, 151 are mounted on the underside ofthe flat plate 140 in such a manner as to be freewheeling about their axes and biased into counter-rotating contact with the corresponding upper rolls 123 and 141. The passive rolls 150 and 151 are biased into contact with the driven rolls 123 and 141 by means of a pair of H-shaped leaf springs (not shown). Each ofthe four rolls 150, 151 is cradled between a pair of parallel arms of one ofthe H-shaped leaf springs. The central portion of each leaf spring is fastened to the plate 140, which is fastened rigidly to the frame ofthe system, so that the relatively stiff arms ofthe H- shaped springs exert a constant biasing pressure against the rolls and push them against the upper rolls 123 and 141. The points of contact between the driven and passive transport rolls are preferably coplanar with the flat upper surface ofthe plate 140 so that currency bills can be positively driven along the top surface ofthe plate in a flat manner. The distance between the axes ofthe two driven transport rolls, and the corresponding counter-rotating passive rolls, is selected to be just short ofthe length ofthe narrow dimension ofthe currency bills. Accordingly, the bills are firmly gripped under uniform pressure between the upper and lower transport rolls within the scanhead area, thereby minimizing the possibility of bill skew and enhancing the reliability ofthe overall scanning and recognition process. The positive guiding arrangement described above is advantageous in that uniform guiding pressure is maintained on the bills as they are transported through the sensor or scanhead area, and twisting or skewing ofthe bills is substantially reduced. This positive action is supplemented by the use ofthe H-springs for uniformly biasing 14 the passive rollers into contact with the active rollers so that bill twisting or skew resulting from differential pressure applied to the bills along the transport path is avoided. The O-rings function as simple, yet extremely effective means for ensuring that the central portions ofthe bills are held flat. As shown in FIG. 2c, the optical encoder 32 is mounted on the shaft ofthe roller 141 for precisely tracking the position of each bill as it is transported through the system, as discussed in detail below in connection with the optical sensing and correlation technique. The encoder 32 also allows the system to be stopped in response to an error occurring or the detection of a "no call" bill. A system employing an encoder to accurately stop a scanning system is described in detail in U.S. Patent No. 5,687,963, which is incorporated herein by reference in its entirety. The single pocket currency system 10 described above in connection with FIGS. 2a-2d, is small and compact, such that it may be rested upon a tabletop or countertop. According to one embodiment, the single-pocket currency handling system 10 has a small size housing 100. The small size housing 100 provides a currency handling system 10 that occupies a small area or "footprint." The footprint is the area that the system 10 occupies on the table top and is calculated by multiplying the width (WI) and the depth (Dl). Because the housing 100 is compact, the currency handling system 10 may be readily used at any desk, work station or teller station. Additionally, the small size housing 100 is light weight allowing the operator to move it between different work stations. According to one embodiment the currency handling system 10 has a height (HI) of about 9 V 2 inches (24.13 cm), width (WI) of about 11 inches (27.94 cm), and a depth (Dl) of about 12 inches (30.48 cm) and weighs approximately 15-20 pounds. In this embodiment, therefore, the currency handling system 10 has a "footprint" of about 11 inches by 12 inches (27.94 cm by 30.48 cm) or approximately 132 square inches (851.61 cm ) which is less than one square foot, and a volume of approximately 1254 cubic inches (20,549.4 cm ) which is less than one cubic foot. Accordingly, the system is sufficiently small to fit on a typical tabletop. The system is able to accommodate various currency, including German currency which is quite long in the X dimension (compared to U.S. currency). The width ofthe system is therefore sufficient to accommodate a German bill which is about 7.087 inches (180 mm) long. The system 15 can be adapted for longer currency by making the transport path wider, which can make the overall system wider. One ofthe contributing factors to the footprint size ofthe currency handling system 10 is the size ofthe currency bills to be handled. For example, in the embodiment described above, the width is less than about twice the length of a U.S. currency bill and the depth is less than about 5 times the width of a U.S. currency bill. Other embodiments ofthe single pocket currency handling system 10 have a height (HI) ranging from 7 inches to 12 inches, a width (WI) ranging from 8 inches to 15 inches, and a depth (Dl) ranging from 10 inches to 15 inches and a weight ranging from about 10-30 pounds. As best seen in FIG. 2b, the currency handling system 10 has a relatively short transport path between the input receptacle and the output receptacle. The transport path beginning at point TB1 (where the idler roll 130 engages the drive roll 123) and ending at point TE1 (where the second driven transport roll 141 and the passive roll 151 contact) has an overall length of about 4V inches. The distance from point TM1 (where the passive transport roll 150 engages the drive roll 123) to point TE1 (where the second driven transport roll 141 and the passive roll 151 contact) is somewhat less than 214 inches, that is, less than the width of a U.S. bill. Thus, The distance from point TB1 (where the idler roll 130 engages the drive roll 123) to point TM1 (where the passive transport roll 150 engages the drive roll 123) is about 2 inches. Turning to FIGS. 3a and 3b, FIG. 3a is a perspective view of a two-pocket currency handling system 20 according to one embodiment ofthe present invention and FIG. 3b is a sectional side view ofthe two-pocket currency handling system of FIG. 3a depicting various transport rolls in side elevation. Furthermore, FIGS. 4a, 4b and 4c portray other multi-pocket embodiments ofthe present invention in which the currency handling system includes three-, four- and six-pockets, respectively. Each ofthe multi- pocket embodiments shown respectively in FIGS. 3a-3b and 4a-4c are described in detail in co-pending U.S. patent application serial number 08/864,423, filed May 28, 1997, entitled "Method and Apparatus for Document Processing" (attorney's docket no. CUMM174), assigned to the assignee ofthe present invention and incorporated herein by reference in its entirety. The currency handling systems depicted in FIGS. 3a-3b and 4a- 16 4c differ from the currency handling systems described in U.S. patent application serial number 08/864,423 in that the systems depicted in FIGS. 3a-3b and 4a-4c employ a color scanhead as described in detail below. As with the single pocket currency system 10 described above in connection with FIGS. 2a-2d, the multi-pocket currency handling systems 20, 30, 40 and 60 shown in FIGS. 3a-3b and 4a-4c are small and compact, such that they may be rested upon a tabletop. According to one embodiment, the two pocket currency handling system 20 enclosed within a housing 200 has a small footprint that may be readily used at any desk, work station or teller station. Additionally, the currency handling system is light weight allowing it to be moved between different work stations. According to one embodiment, the two-pocket currency handling system 20 has a height (H2) of about 18 inches, width (W2) of about 13 4 inches, and a depth (D2) of about 17! inches and weighs approximately 70 pounds. Accordingly, the currency handling system 10 has a footprint of about 13V4 inches by about 17 inches or approximately 230 square inches or about VΛ square feet and a volume of about 4190 cubic inches or slightly more than 2 / 3 cubic feet, which is sufficiently small to conveniently fit on a typical tabletop. One ofthe contributing factors to the footprint size ofthe currency handling system 20 is the size of the currency bills to be handled. For example in the embodiment described above the width is approximately 2!4 times the length of a U.S. currency bill and the depth is approximately 7 times the width of a U.S. currency bill. According to another embodiment, the two-pocket currency handling system 20 has a height (H2) ranging from 15-20 inches, a width (W2) ranging from 10-15 inches, and a depth (D2) ranging from 15-20 inches and a weight ranging from about 35-50 pounds. The currency handling system 10 has a footprint ranging from 10-15 inches by 15-20 inches or approximately 150-300 square inches and a volume of about 2250-6000 cubic inches, which is sufficiently small to conveniently fit on a typical tabletop. According to another embodiment, the small size housing 200 may have a height (H2) of about 20 inches or less, width (W2) of about 20 inches or less, and a depth (D2) of about 20 inches or less and weighs approximately 50 pounds or less. As best seen in FIG. 3b, the currency handling system 20 has a short transport path between the input receptacle and the output receptacle. The transport path has a length of about 10V4 17 inches between the beginning ofthe transport path at point TB2 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260 at point TM1 and has an overall length of about 15/4 inches from point TB2 to point TE2 (where the rolls 286 and 282 contact). Similarly, the three-, four- and six-pocket systems 30, 40, 60 (FIGS. 4a-4c), in some embodiments, are constructed with generally the same footprint as the two pocket systems, allowing them to be rested upon a typical tabletop or countertop. Generally, however, where the three-, four- and six-pocket systems are constructed with the same footprint as the two-pocket system, they will be "taller" than the two-pocket system, with the relative heights ofthe respective systems corresponding generally to the number of pockets. Thus, in general, where the multi-pocket systems have approximately the same size footprint, the six-pocket system 60 (FIG. 4c) will be taller than the four-pocket system 40 (FIG. 4b), which in turn will be taller than the three-pocket system 30 (FIG. 4a) and the two-pocket system 20 (FIGS. 3a and 3b). As shown in FIGS. 4a-4c, the three, four and six pocket currency handling systems have the same width as the two pocket currency handling system shown in FIG. 3a, namely, about 13 X A inches. The three pocket currency handling system 30 of FIG. 4a has a height H3 of about 23 inches and a depth D3 of about 19% inches. The transport path ofthe three-pocket system has a length of about lO'Λ inches between the beginning ofthe transport path at point TB3 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TM1, a length of about 6V1 inches between the beginning ofthe transport path at point TB3 and the tip ofthe diverter 260b at point TM2, and has an overall length of about 2114 inches from point TB3 to point TE3 (where the rolls 286b and 282b contact). According to another embodiment, the three pocket currency handling system has a height H3 ranging from 20-25 inches and a depth D3 ranging from 15-25 inches. The transport path ofthe three-pocket system has a length ranging from 8-12 inches between the beginning ofthe transport path at point TB3 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TM1, a length ranging from 12-18 inches between the beginning ofthe transport path at point TB3 and the tip ofthe diverter 260b at point TM2, and has an overall length ranging from 18-25 inches from point TB3 to point TE3 (where the rolls 286b and 282b contact). 18 The four pocket currency handling system 40 of FIG. 4b has a height H4 of about 28/4 inches and a depth D4 of about 22 !4 inches. The transport path ofthe four-pocket system has a length of about 10/4 inches between the beginning ofthe transport path at point TB4 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TMl , a length of about 16!4 inches between the beginning ofthe transport path at point TB4 and the tip ofthe diverter 260b at point TM2, a length of about 22/4 inches between the beginning ofthe transport path at point TB4 and the tip ofthe diverter 260c at point TM3, and an overall length of 27.193 inches from point TB4 to point TE4 (where the rolls 286c and 282c contact). In another embodiment, the four pocket currency handling system has a height H4 ranging from 25-30 inches and a depth D4 ranging from 20-25 inches. The transport path ofthe four-pocket system has a length ranging from 8-12 inches between the beginning ofthe transport path at point TB4 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TMl, a length ranging from 12-20 inches between the beginning ofthe transport path at point TB4 and the tip ofthe diverter 260b at point TM2, a length ranging from 18-26 inches between the beginning of the transport path at point TB4 and the tip ofthe diverter 260c at point TM3, and an overall length ranging from 22-32 inches from point TB4 to point TE4 (where the rolls 286c and 282c contact). The six pocket currency handling system 60 of FIG. 4c has a height H6 of about 39% inches and a depth D6 of about 27'/ inches. The transport path ofthe six-pocket system has a length of about 10 ! inches between the beginning ofthe transport path at point TB6 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TMl, a length of about 16/4 inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260b at point TM2, a length of about 22Vι inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260c at point TM3, a length of about 28 VΛ inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260d at point TM4, a length of about 34 inches between the beginning ofthe transport path at point TB6 and the tip of the diverter 260e at point TM5, and an overall length of about 39 inches from point TB6 to point TE6 (where the rolls 286e and 282e contact). 19 In another embodiment, the six pocket currency handling system has a height H6 ranging from 35-45 inches and a depth D6 ranging from 22-32 inches. The transport path ofthe six-pocket system has a length ranging from 8-12 inches between the beginning of the transport path at point TB6 (where the idler roll 230 engages the drive roll 223) and the tip ofthe diverter 260a at point TMl, a length ranging from 12-20 inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260b at point TM2. a length ranging from 18-26 inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260c at point TM3, a length ranging from 22-32 inches between the beginning ofthe transport path at point TB6 and the tip ofthe diverter 260d at point TM4, a length ranging from 30-40 inches between the beginning of the transport path at point TB6 and the tip ofthe diverter 260e at point TM5, and an overall length ranging from 32-42 inches from point TB6 to point TE6 (where the rolls 286e and 282e contact). Referring now to FIGS. 3a, 3b, 4a, 4b and 4c, parts and components similar to those in the embodiment of FIGS. 2a-2d are designated by similar reference numerals. For example, parts designated by 100 series reference numerals in FIGS. 2a-2d are designated by similar 200 series reference numerals in FIGS. 3a-3b and 4a-4c, while parts which we duplicated one or more times, are designated by like reference numerals with suffixes a, b, c, etc. The mechanical portions ofthe multi-pocket currency handling systems include a housing 200 having the input receptacle 36 for receiving a stack of bills to be processed. The receptacle 36 is formed by downwardly sloping and converging walls 205 and 206 (see FIG. 3b) formed by a pair of removable covers (not shown) which snap onto a frame. The converging wall 206 supports a removable hopper (not shown) that includes vertically disposed side walls (not shown). One embodiment of an input receptacle was described and illustrated in detail above and applies to the multi -pocket currency handling systems 20, 30, 40, 60. The multi-pocket currency handling systems 20, 30, 40, 60 also include an operator interface 32b as described for the single pocket currency handling device 10. From the input receptacle 36, the currency bills in each ofthe multi-pocket systems (FIGS. 3a-3b, 4a-4c) are moved in seriatim from the bottom of a stack of bills along a curved guideway 211, which receives bills moving downwardly and rearwardly 20 and changes the direction of travel to a forward direction. The curvature of the guideway 211 corresponds substantially to the curved periphery of a drive roll 223 so as to form a narrow passageway for the bills along the rear side ofthe drive roll 223. An exit end of the curved guideway 211 directs the bills onto the transport plate 240 which carries the bills through an evaluation section and to one ofthe output receptacles 34. In the two-pocket embodiment (FIG. 3b), for example, stacking ofthe bills is accomplished by a pair of driven stacking wheels 35a and 37a for the first or upper output receptacle 34a and by a pair of stacking wheels 35b and 37b for the second or bottom output receptacle 34b. The stacker wheels 35a, 37a and 35b, 37b are supported for rotational movement about respective shafts 215a, b journalled on a rigid frame and driven by a motor (not shown). Flexible blades ofthe stacker wheels 35a and 37a deliver the bills onto a forward end of a stacker plate 214a. Similarly, the flexible blades ofthe stacker wheels 35b and 37b deliver the bills onto a forward end of a stacker plate 214b. A diverter 260 directs the bills to either the first or second output receptacle 34a, 34b. When the diverter is in a lower position, bills are directed to the first output receptacle 34a. When the diverter 260 is in an upper position, bills proceed in the direction ofthe second output receptacle 34b. The multi-pocket document evaluation devices in FIG. 4a-4c have a transport mechanism which includes a series of transport plates or guide plates 240 for guiding currency bills to one of a plurality of output receptacles 214. The transport plates 240 according to one embodiment are substantially flat and linear without any protruding features. Before reaching the output receptacles 214, a bill is moved past the sensors or scanhead to be, for example, evaluated, analyzed, authenticated, discriminated, counted and/or otherwise processed. The multi-pocket document evaluation devices move the currency bills in seriatim from the bottom of a stack of bills along the curved guideway 211 which receives bills moving downwardly and rearwardly and changes the direction of travel to a forward direction. An exit end ofthe curved guideway 211 directs the bills onto the transport plate 240 which carries the bills through an evaluation section and to one ofthe output receptacles 214. A plurality of diverters 260 direct the bills to the output receptacles 214. When a diverter 260 is in its lower position, bills are directed to the 21 corresponding output receptacle 214. When a diverter 260 is in its upper position, bills proceed in the direction ofthe remaining output receptacles. The multi-pocket currency evaluation devices of FIGS. 3a-3b and 4a-4c according to one embodiment includes passive rolls 250, 251 which are mounted to shafts 254, 255 on an underside ofthe first transport plate 240 and are biased into counter-rotating contact with their corresponding driven upper rolls 223 and 241. These embodiments include one or more follower plates 262, 278, etc. which are substantially free from surface features and are substantially smooth like the transport plates 240. The follower plates 262 and 278 are positioned in spaced relation to respective transport plates 240 so as to define a currency pathway therebetween. In one embodiment, follower plates 262 and 278 have apertures only where necessary for accommodation of passive rolls 268, 270, 284, and 286. The follower plate 262 works in conjunction with the upper portion ofthe associated transport plate 240 to guide a bill from the passive roll 251 to a driven roll 264 and then to a driven roll 266. The passive rolls 268, 270 are biased by H-springs into counter-rotating contact with the corresponding driven rolls 264 and 266. It will be appreciated that any ofthe stacker arrangements heretofore described may be utilized to receive currency bills, after they have been evaluated by the system. Without departing from the invention, however, bills transported through the system in learn mode, rather than being transported from the input receptacle to the output receptacle(s), could be transported from the input receptacle past the sensors, then in reverse manner delivered back to the input receptacle. I. SCANNING REGION FIG. 5 a is an enlarged sectional side view depicting the scanning region according to one embodiment ofthe present invention. According to various embodiments, this scanhead arrangement is employed in the currency handling systems described above in connection with FIGS. l-4c. According to the depicted embodiment, the scanning region along the transport path comprises both a standard optical scanhead 70 and a full color scanhead 300. Driven transport rolls 523 and 541 in cooperation with passive rolls 550 and 551 engage and transport bills past the scanning region in a 22 controlled manner. The transport mechanics are described in more detail in U.S. Patent No. 5,687,963. The standard scanhead 70 differs somewhat in its physical appearance from that described in U.S. Patent No. 5,687,963 mentioned above and incorporated herein by reference in its entirety but otherwise is identical in terms of operation and function. The upper standard scanhead 70 is used to scan one side of bills while the lower full color scanhead 300 is used to scan the other side of bills. These scanheads are coupled to processors. For example, the upper scanhead 70 is coupled to a 68HC16 processor by Motorola of Schaumburg, IL. The lower full color scanhead 300 is coupled to a TMS 320C32 DSP processor by Texas Instruments of Dallas, TX. According to one embodiment that will be described in more detail below, when processing U.S. bills, the upper scanhead 70 is used in the manner described in U.S. Patent No. 5,687,963 while the full color scanhead 300 is used in a manner described later herein. FIG. 5b is an enlarged sectional side view depicting the scanheads of FIG. 5a without some ofthe rolls associated with the transport path. Again, depicted in this illustration, is the standard scanhead 70 and a color module 581 comprising the color scanhead 300 and an UV sensor 340 and its accompanying UV light tube 342. The details of how the UV sensor 340 operates are described in U.S. Patent No. 5,640,463 and U.S. Patent Application Serial No. 08/798,605 which are incorporated herein by reference in their entirety. FIG. 5c illustrates the scanheads of FIGS. 5a and 5b in a front view. A. Standard Scanhead According to one embodiment, the standard scanhead 70 (also shown in FIGS. 15a and 15b) includes two standard photodetectors 74a and 74b (see FIGS. 5a and 5b) and two photodetectors 95 and 97 (the density sensors), illustrated in FIG. 15b. Two light sources are provided for the photodetectors as described in more detail in U.S. Patent No. 5,295,196 incorporated herein by reference. The standard scanhead employs a mask having two rectangular slits 360 and 362 (see FIG. 15b) therein for permitting light reflected off passing bills to reach the photodetectors 74a and 74b, which are behind the slits 360, 362, respectively. One photodetector 74b is associated with a narrow slit 362 and may optionally be used to detect the fine borderline present on U.S. currency, when suitable cooperating circuits are provided. The other photodetector 74a associated 23 with a wider slit 360 may be used to scan the bill and generate optical patterns used in the discrimination process. FIG. 7 is a functional block diagram ofthe standard optical scanhead 70, and FIG. 8 is a functional block diagram ofthe full color scanhead 300 of FIG. 5. The standard scanhead 70 is an optical scanhead that scans for characteristic information from a currency bill 44. According to one embodiment, the standard optical scanhead 70 includes a sensor 74 having, for example, two photodetectors each having a pair of light sources 72 directing light onto the bill transport path so as to illuminate a substantially rectangular area 48 upon the surface ofthe currency bill 44 positioned on the transport path adjacent the scanhead 70. As illustrated in FIGS. 15a,b, one ofthe photodetectors 74b is associated with a narrow rectangular slit 362 and the other photodetector 74a is associated with a wider rectangular slit 360. Light reflected off the illuminated area 48 is sensed by the sensor 74 positioned between the two light sources 72. The analog output ofthe photodetectors 74 is converted into a digital signal by means ofthe analog-to- digital (ADC) converter unit 52 (FIG. 20) whose output is fed as a digital input to the central processing unit (CPU) 54 as described above in connection with FIG. 1. Alternatively, especially in embodiments of currency handling system designed to process currency other than U.S. currency, a single photodetector 74a having the wider slit 360 may be employed without photodetector 74b. According to one embodiment, the bill transport path is defined in such a way that the transport mechanism 38 (FIG. 1) moves currency bills with the narrow dimension ofthe bills being parallel to the transport path and the scan direction SD. As a bill 44 traverses the scanhead 70, the illuminated area 48 moves to define a coherent light strip which effectively scans the bill across the narrow dimension (W) ofthe bill. In the embodiment depicted, the transport path is so arranged that a currency bill 44 is scanned across a central section ofthe bill along its narrow dimension, as shown in FIG. 9a. The scanhead functions to detect light reflected from the bill 44 as the bill 44 moves past the scanhead 70 to provide an analog representation ofthe variation in reflected light, which, in turn, represents the variation in the dark and light content ofthe printed pattern or indicia on the surface ofthe bill 44. This variation in light reflected from the narrow dimension scanning ofthe bills serves as a measure for distinguishing, with a high degree 24 of confidence, among a plurality of currency denominations which the system is programmed to handle. The standard optical scanhead 70 and standard intensity scanning process is described in detail in U.S. Patent No. 5,687,963 entitled "Method and Apparatus for Discriminating and Counting Documents," assigned to the assignee ofthe present invention and incorporated herein by reference in its entirety. The standard optical scanhead 70 produces a series of such detected reflectance signals across the narrow dimension ofthe bill, or across a selected segment thereof, and the resulting analog signals are digitized under control ofthe PROCESSOR 54 to yield a fixed number of digital reflectance data samples. The data samples are then subjected to a normalizing routine for processing the sampled data for improved correlation and for smoothing out variations due to "contrast" fluctuations in the printed pattern existing on the bill surface. The normalized reflectance data represents a characteristic pattern that is unique for a given bill denomination and provides sufficient distinguishing features among characteristic patterns for different currency denominations. In order to ensure strict correspondence between reflectance samples obtained by narrow dimension scanning of successive bills, the reflectance sampling process is preferably controlled through the PROCESSOR 54 (FIG. 1) by means of an optical encoder 14 (FIG. 1) which is linked to the bill transport mechanism 38 (FIG. 1) and precisely tracks the physical movement ofthe bill 44 past the scanhead 70. More specifically, the optical encoder 14 is linked to the rotary motion ofthe drive motor which generates the movement imparted to the bill along the transport path. In addition, the mechanics ofthe feed mechanism ensure that positive contact is maintained between the bill and the transport path, particularly when the bill is being scanned by the scanhead. Under these conditions, the optical encoder 14 is capable of precisely tracking the movement ofthe bill 44 relative to the portion ofthe bill 48 illuminated by the scanhead 70 by monitoring the rotary motion ofthe drive motor. According to one embodiment, in the case of U.S. currency bills, the output ofthe sensor 74a is monitored by the PROCESSOR 54 to initially detect the presence ofthe bill adjacent the scanhead and, subsequently, to detect the starting point ofthe printed pattern on the bill, as represented by the borderline 44a which typically encloses the printed indicia on U.S. currency bills. Once the borderline 44a has been detected, the 25 optical encoder 14 is used to control the timing and number of reflectance samples that are obtained from the output ofthe sensor 74b as the bill 44 moves across the scanhead 70. According to another embodiment, in the case of currency bills other than U.S. currency bills, the outputs ofthe sensor 74 are monitored by the PROCESSOR 54 to initially detect the leading edge 44b ofthe bill 44 adjacent the scanhead. Because most currencies of currency systems other than the U.S. do not have the borderline 44a, the PROCESSOR 54 must detect the leading edge 44b for non U.S. currency bills. Once the leading edge 44b has been detected, the optical encoder 14 is used to control the timing and number of reflectance samples that are obtained from the outputs ofthe sensors 74 as the bill 44 moves across the scanhead 70. The use ofthe optical encoder 14 for controlling the sampling process relative to the physical movement of a bill 44 across the scanhead 70 is also advantageous in that the encoder 14 can be used to provide a predetermined delay following detection ofthe borderline 44a or leading edge 44b prior to initiation of samples. The encoder delay can be adjusted in such a way that the bill 44 is scanned only across those segments which contain the most distinguishable printed indicia relative to the different currency denominations. In the case of U.S. currency, for instance, it has been determined that the central, approximately two-inch (approximately 5 cm) portion of currency bills, as scanned across the central section ofthe narrow dimension ofthe bill (see segment SEG S of FIG. 9a), provides sufficient data for distinguishing among the various U.S. currency denominations. Accordingly, the optical encoder 14 can be used to control the scanning process so that reflectance samples are taken for a set period of time and only after a certain period of time has elapsed after the borderline 44a is detected, thereby restricting the scanning to the desired central portion ofthe narrow dimension ofthe bill 48. FIGS. 9a-9c illustrate the standard intensity scanning process for U.S. currency bills in more detail. Referring to FIG. 9a, as a bill 44 is advanced in a direction parallel to the narrow edges ofthe bill, scanning via a slit in the scanhead 70 is effected along a segment SEG S ofthe central portion ofthe bill 44. This segment SEG S begins a fixed distance D s inboard ofthe borderline 44a. As the bill 44 traverses the scanhead 70, a 26 portion or area ofthe segment SEG S is illuminated, and the sensor 74 produces a continuous output signal which is proportional to the intensity ofthe light reflected from the illuminated portion or area at any given instant. This output is sampled at intervals controlled by the encoder, so that the sampling intervals are precisely synchronized with the movement ofthe bill across the scanhead. As illustrated in FIGS. 9b-9c, it is preferred that the sampling intervals be selected so that the areas that are illuminated for successive samples overlap one another. The odd-numbered and even-numbered sample areas have been separated in FIGS. 9b and 9c to more clearly illustrate this overlap. For example, the first and second areas SI and S2 overlap each other, the second and third areas S2 and S3 overlap each other, and so on. Each adjacent pair of areas overlap each other. In the illustrative example, this is accomplished by sampling areas that are 0.050 inch (0.127 cm) wide, L, at 0.029 inch (0.074 cm) intervals, along a segment SEG S that is 1.83 inch (4.65 cm) long (64 samples). The center-to-center distance N between two adjacent samples is 0.029 inches and the center-to-center distance M between two adjacent even or odd samples is 0.058 inches. Sampling is initiated at a distance D s of .389 inches inboard ofthe leading edge 44b ofthe bill. While it has been determined that the scanning ofthe central area of a U.S. bill provides sufficiently distinct patterns to enable discrimination among the plurality of U. S. currency denominations, the central area or the central area alone may not be suitable for bills originating in other countries. For example, for bills originating from Country 1 , it may be determined that segment SEG ! (FIG. 9d) provides a more preferable area to be scanned, while segment SEG 2 , (FIG. 9d) is more preferable for bills originating from Country 2. Alternatively, in order to sufficiently discriminate among a given set of bills, it may be necessary to scan bills which are potentially from such set along more than one segment, e.g., scanning a single bill along both SEG ] and SEG 2 . To accommodate scanning in areas other than the central portion of a bill, multiple standard optical scanheads may be positioned next to each other along a direction lateral to the direction of bill movement. Such an arrangement of standard optical scanheads permit a bill to be scanned along different segments. Various multiple scanhead arrangements are described in more detail in U.S. Patent No. 5,652,802 entitled " Method and Apparatus 27 for Document Identification" assigned to the assignee ofthe present application and incorporated herein by references in its entirety. The standard optical sensing and correlation technique is based upon using the above process to generate a series of stored intensity signal patterns using genuine bills for each denomination of currency that the currency handling system 10 is programmed to recognize. According to one embodiment, four sets of master intensity signal samples are generated and stored within the memory 56 (see FIG. 1) for each scanhead for each detectable currency denomination. In the case of U.S. currency, the sets of master intensity signal samples for each bill are generated from standard optical scans, performed on one or both surfaces ofthe bill and taken along both the "forward" and "reverse" directions relative to the pattern printed on the bill. In adapting this technique to U.S. currency, for example, sets of stored intensity signal samples are generated and stored for seven different denominations of U.S. currency, i.e., $l, $2, $5, $10, $20, $50 and $100. For bills which produce significant pattern changes when shifted slightly to the left or right, such as the $ 10 bill in U.S. currency, two patterns may be stored for each ofthe "forward" and "reverse" directions, each pair of patterns for the same direction represent two scan areas that are slightly displaced from each other along the long dimension ofthe bill. Once the master patterns have been stored, the pattern generated by scanning a bill under test is compared by the PROCESSOR 54 with each of the master patterns of stored standard intensity signal samples to generate, for each comparison, a correlation number representing the extent of correlation, i.e., similarity between corresponding ones ofthe plurality of data samples, for the sets of data being compared. When using the upper standard scanhead 70, the PROCESSOR 54 is programmed to identify the denomination ofthe scanned bill as the denomination that corresponds to the set of stored intensity signal samples for which the correlation number resulting from pattern comparison is found to be the highest. In order to preclude the possibility of mischaracterizing the denomination of a scanned bill, as well as to reduce the possibility of spurious notes being identified as belonging to a valid denomination, a bi-level threshold of correlation is used as the basis for making a "positive" call. Such methods are disclosed in U.S. Patent Nos. 5,295,196 entitled "Method and Apparatus for Currency 28 Discrimination and Counting" and U.S. Patent No. 5,687,963 which are incorporated herein by reference in their entirety. If a "positive" call can not be made for a scanned bill, an error signal is generated. When master characteristic patterns are being generated, the reflectance samples resulting from the scanning by scanhead 70 of one or more genuine bills for each denomination are loaded into corresponding designated sections within the memory 56. During currency discrimination, the reflectance values resulting from the scanning of a test bill are sequentially compared, under control ofthe correlation program stored within the memory 56, with the corresponding master characteristic patterns stored within the memory 56. A pattern averaging procedure for scanning bills and generating master characteristic patterns is described in U.S. Patent No. 5,633,949 entitled "Method and Apparatus for Currency Discrimination," which is incorporated herein by reference in its entirety. B. Full Color Scanhead Returning to FIG. 8, there is shown a functional block diagram of one cell 334 of the color scanhead 300 according to one embodiment ofthe present invention. As will be described in more detail below, the color scanhead may comprise a plurality of such cells. The illustrative cell includes a pair of light sources 308 (e.g. fluorescent tubes) directing light onto the bill transport path. A single light source, e.g., single fluorescent tube or other light source, could be used without departing from the invention. The light sources 308 illuminate a substantially rectangular area 48 upon a currency bill 44 to be scanned. The cell comprises three filters 306 and three sensors 304. Light reflected off the illuminated area 48 passes through filters 306r, 306b and 306g positioned below the two light sources 308. Each ofthe filters 306r, 306b and 306g transmits a different component ofthe reflected light to corresponding sensors or photodiodes 304r, 304b and 304g, respectively. In one embodiment, the filter 306r transmits only a red component ofthe reflected light, the filter 306b transmits only a blue component ofthe reflected light and the filter 306g transmits only a green component ofthe reflected light to the corresponding sensors 304r, 304b and 304g, respectively. The specific wavelength ranges transmitted by each filter beginning at 10% transmittance are: 29 Red 580 nm to 780 nm, Blue 400 nm to 510 nm, Green 480 nm to 580 nm. The specific wavelength ranges transmitted by each filter beginning at 80% transmittance are: Red 610 nm to 725 nm, Blue 425 nm to 490 nm, Green 525 nm to 575 nm. Upon receiving their corresponding color components ofthe reflected light, the sensors 304r, 304b and 304g generate red, blue and green analog outputs, respectively, representing the variations in red, blue and green color content in the bill 44. These red, blue and green analog outputs ofthe sensors 304r, 304b and 304g, respectively, are amplified by the amplifier 58 (FIG. 1) and converted into a digital signal by the analog- to-digital converter (ADC) unit 52 whose output is fed as a digital input to the central processing unit (CPU) 54 as described above in conjunction with FIG. 1. Similar to the operation ofthe standard optical scanhead 70 embodiment described above, the bill transport path is defined in such a way that the transport mechanism 38 moves currency bills with the narrow dimension ofthe bills being parallel to the transport path and the scan direction. The color scanhead 300 functions to detect light reflected from the bill as the bill moves past the color scanhead 300 to provide an analog representation ofthe color content in reflected light, which, in turn, represents the variation in the color content ofthe printed pattern or indicia on the surface of the bill. The sensors 304r, 304b and 304g generate the red, blue and green analog representations ofthe red, blue and green color content ofthe printed pattern on the bill. This color content in light reflected from the scanned portion ofthe bills serves as a measure for distinguishing among a plurality of currency types and denominations which the system is programmed to handle. According to one embodiment, the outputs of an edge sensor (to be described below in connection with FIG. 13) and the green sensors 304g of one ofthe color cells are monitored by the PROCESSOR 54 to initially detect the presence ofthe bill 44 adjacent the color scanhead 300 and, subsequently, to detect the edge 44b ofthe bill. Once the edge 44b has been detected, the optical encoder 14 is used to control the timing 30 and number of red, blue and green samples that are obtained from the outputs ofthe sensors 304r, 304b and 304g as the bill 44 moves past the color scanhead 300. In order to ensure strict correspondence between the red, blue and green signals obtained by narrow dimension scanning of successive bills, as illustrated in FIG. 10b, the color sampling process is preferably controlled through the PROCESSOR 54 by means ofthe optical encoder 14 (see FIG. 1) which is linked to the bill transport mechanism 38 and precisely tracks the physical movement ofthe bill 44 across the color scanhead 300. Bill tracking and control using the optical encoder 14 and the mechanics ofthe transport mechanism are accomplished as described above in connection with the standard scanhead. The use ofthe optical encoder 14 for controlling the sampling process relative to the physical movement of a bill 44 past the color scanhead 300 is also advantageous in that the encoder 14 can be used to provide a predetermined delay following detection of the bill edge 44b prior to initiation of samples. The encoder delay can be adjusted in such a way that the bill 44 is scanned only across those segments which contain the most distinguishable printed indicia relative to the different currency denominations. FIGS. lOa-lOc illustrate the color scanning process. Referring to FIG. 10a, as a bill 44 is advanced in a direction parallel to the narrow edges ofthe bill, five adjacent color cells 334 (e.g., cells 334a-334e of FIG. 13b to be described below) in the color scanhead 300 scan along scan areas, segments or strips SA1, SA2, SA3, SA4 and SA5, respectively, of a central portion ofthe bill 44. As the bill 44 traverses the color scanhead 300, each color cell 334 views its respective scan area, segment or strip SA1, SA2, SA3, SA4 and SA5, and its sensors 304r, 304b and 304g continuously produce red, blue and green output signals which are proportional to the red, blue and green color content ofthe light reflected from the illuminated area or strip at any given instant. These red, blue and green outputs are sampled at intervals controlled by the encoder 14, so that the sampling intervals are precisely synchronized with the movement ofthe bill 44 across the color scanhead 300. FIG. 10b illustrates how 64 incremental sample areas S1-S64 are sampled using 64 sampling intervals along one ofthe five color cell scan areas SA1, SA2, SA3, SA4 or SA5. To account for the lateral shifting of bills in the transport path, it is preferred to store two or more patterns for each denomination of currency. The patterns represent 31 scanned areas that are slightly displaced from each other along the lateral dimension of the bill. In one embodiment, only three ofthe five color cells 334 (e.g., cells 334a, 334c and 334e of FIG. 13b) in the color scanhead 300 are used to scan U.S. currency. Thus, only the scan areas SA1, SA3 and SA5 of FIG. 10a are scanned. As illustrated in FIGS. 10b and 10c, in similar fashion to the above-described operation in FIGS. 9a- 9b, the sampling intervals are preferably selected so that the successive samples overlap one another. The odd-number and even numbered sample areas have been separated in FIGS. 10b and 10c to more clearly illustrate this overlap. For example the first and second areas S 1 and S2 overlap each other, the second and third areas overlap each other and so on. Each adjacent pair of areas overlap each other. For example, this is accomplished by sampling areas that are 0.050 inch (0.127 cm) wide, L, at 0.035 inch intervals, along a segment S that is 2.2 inches (5.59 cm) long to provide 64 samples across the bill. The center-to-center distance Q between two adjacent samples is 0.035 inches and the center-to-center distance P between two adjacent even or odd samples is 0.07 inches. Sampling is initiated at a distance D c of A inch inboard of the leading edge 44b ofthe bill. In one embodiment, the sampling is synchronized with the operating frequency of the fluorescent tubes employed as the light sources 308 ofthe color scanhead 300. According to one embodiment, fluorescent tubes manufactured by Stanley of Japan having a part number of CB Y26-220NO are used. These fluorescent tubes operate at a frequency of 60 KHz, so the intensity of light generated by the tubes varies with time. To compensate for noise, the sampling ofthe sensors 304 is synchronized with the tubes' frequency. FIG. 11 illustrates the synchronization ofthe sampling with the operating frequency ofthe fluorescent tubes. The sampling by the sensors 304 is controlled so that the sensors 304 sample a bill at the same point during successive cycles, such as at times tl, t2, t3, and etc. In a preferred embodiment, the color sensing and correlation technique is based upon using the above process to generate a series of stored hue and brightness signal patterns using genuine bills for each denomination of currency that the system is programmed to discriminate. The red, blue and green signals from each ofthe color cells 32 334 are first summed together to obtain a brightness signal. For example, if the red, blue and green sensors produced 2v, 2v, and lv respectively, the brightness signal would equal 5v. If the total output from the sensors is lOv when exposed to a white sheet of paper, then the brightness percentage corresponding to a 5v brightness signal would be 50%. Using the red, blue and green signals, a red hue, a blue hue and a green hue can be determined. A hue signal indicates the percentage of total light that a particular color of light constitutes. For example, dividing the red signal by the sum ofthe red, blue and green signals provides the red hue signal, dividing the blue signal by the sum ofthe red, blue and green signals provides the blue hue signal, and dividing the green signal by the sum ofthe red, blue and green signals provides the green hue signal. In an alternative embodiment, the individual red, blue and green output signals may be used directly for a color pattern analysis. FIGS. 12a-e illustrate graphs of hue and brightness signal patterns obtained by color scanning a front side of a $10 Canadian bill with the color scanhead 300 of FIG. 13 (to be discussed below). FIG. 12a corresponds to the hues and brightness signal patterns generated from the color outputs of color cell 334a, FIG. 12b corresponds to outputs of color cell 334b, FIG. 12c corresponds to outputs of color cell 334c, FIG. 12d corresponds to outputs of color cell 334d, and FIG. 12e corresponds to outputs of color cell 334e. On the graphs, the y-axis is the percentage of brightness and the percentage ofthe three hues, on a scale of zero to one thousand, representing percent times 10 (% x 10). The x-axis is the number of samples taken for each bill pattern. See the normalization and/or correlation discussion below. According to one embodiment ofthe color sensing and correlation technique, four sets of master red hues, master green hues and master brightness signal samples are generated and stored within the memory 56 (see FIG. 1), for each programmed currency denomination, for each color sensing cell. The four sets of samples correspond to four possible bill orientations "forward," "reverse," "face up" and "face down." In the case of Canadian bills, the sets of master hue and brightness signal samples for each bill are generated from color scans, performed on the front (or portrait) side ofthe bill and taken along both the "forward" and "reverse" directions relative to the pattern printed on the bill. Alternatively, the color scanning may be performed on the back side of Canadian currency bills or on either surface of other bills. Additionally, the color scanning may be performed on both sides of a bill by a pair of color scanheads 300 such as a pair of scanheads 300 of FIG. 13 located on opposite sides ofthe transport plate 140. In adapting this technique to Canadian currency, for example, master sets of stored hue and brightness signal samples are generated and stored for eight different denominations of Canadian bills, namely, $1, $2, $5, $10, $20, $50, $100 and $1,000. Thus, for each denomination, master patterns are stored for the red, green and brightness patterns for each ofthe four possible bill orientations (face up feet first, face up head first, face down feet first, face down head first) and for each of three different bill positions (right, center and left) in the transport path. This yields 36 patterns for each denomination. Accordingly, when processing the eight Canadian denominations, a set of 288 different master patterns are stored within the memory 56 for subsequent correlation purposes. IL BRIGHTNESS NORMALIZING TECHNIQUE A simple normalizing procedure is utilized for processing raw test brightness samples into a form which is conveniently and accurately compared to corresponding master brightness samples stored in an identical format in memory 56. More specifically, as a first step, the mean value X for the set of test brightness samples X, -r = ∑ ι=0 n (containing "n" samples) is obtained for a bill scan as below: Subsequently, a normalizing factor Sigma ("s") is determined as being equivalent to the sum ofthe square ofthe difference between each sample and the mean, as normalized by the total number n of samples. More specifically, the normalizing factor " IN, - Nf Σ is calculated as below: 34 In the final step, each raw brightness sample is normalized by obtaining the difference between the sample and the above-calculated mean value and dividing it by X = ^ 3 the square root ofthe normalizing factor s as defined by the following equation: III. PHYSICAL EMBODIMENT OF A MULTI-CELL COLOR SCANHEAD A physical embodiment of a full color, multi-cell compatible scanhead will now be described in connection with FIGS. 13a-13g. The scanhead 300 includes a body 302 that has a plurality of filter and sensor receptacles 303 along its length as best seen in FIG. 13b. Each receptacle 303 is designed to receive a color filter 306 (which may be a clear piece of glass) and a sensor 304, one set of which is shown in an exploded view in FIG. 13b (also see in FIG. 13f). A filter 306 is positioned proximate a sensor 304 to transmit light of a given wavelength range of wavelengths to the sensor 304. As illustrated in FIG. 13b, one embodiment ofthe scanhead housing 302 can accommodate forty-three sensors 304 and forty-three filters 306. A set of three filters 306 and three sensors 304 comprise a single color cell 334 on the scanhead 300. According to one embodiment, three adjacent receptacles 303 having three different primary color filters therein constitute one full color cell, e.g., 334a. However, as described elsewhere herein, only two color filters and sensors may be utilized, with the value ofthe third primary color content being derived by the processor. By primary colors it is meant colors from which all other colors may be generated, which includes both additive primary colors (red, green, and blue) and subtractive primary colors (magenta, yellow, and cyan). According to one embodiment, the three color filters 306 are standard red, green, and blue dichroic color separation glass filters. One side of each glass filter is coated with a standard hot mirror for infrared light blocking. According to one embodiment, each filter is either a red filter, part number 1930, a green filter, part number 1945, or a blue filter, part number 1940 available from Reynard Corporation of San Clemente, CA. According to one embodiment, the sensors 304 are photodiodes, part number BPW34, made by Centronics Corp. of Newbury Park, CA. 35 According to one embodiment, sensors that have a large sensor area are chosen. The sensors 304 provide the color analog output signals to perform the color scanning as described above. The color scanhead 300 is preferably positioned proximate the bill transport plate (see 140 in FIG. 2b, 240 in FIGS. 3b, 4a, 4b and 4c and 540 in FIG. 5a). The scanhead 300 further includes a reference sensor 350, described in more detail below in connection with section V. STANDARD MODE/ LEARN MODE. As seen in FIG. 13f, the sensors 304 and filters 306 are positioned within the filter and sensor receptacles 303 in the body 302 ofthe scanhead 300. Each ofthe receptacles has ledges 332 for holding the filters 306 in the desired positions. The sensors 304 are positioned immediately behind their corresponding filters 306 within the receptacle 303. FIG. 13e illustrates one full color cell such as cell 334a on the scanhead 300. The color cell 334a comprises a receptacle 303r for receiving a red filter 306r (not shown) adapted to pass only red light to a corresponding red sensor 304r (not shown). As mentioned above, the specific wavelength ranges transmitted by each filter beginning at 10% transmittance are: Red 580 nm to 780 nm, Blue 400 nm to 510 nm, Green 480 nm to 580 nm. The specific wavelength ranges transmitted by each filter beginning at 80% transmittance are: Red 610 nm to 725 nm, Blue 425 nm to 490 nm, Green 525 nm to 575 nm. The cell further comprises a blue receptacle 303b for receiving a blue filter 306b (not shown) adapted to pass only blue light to a corresponding blue sensor 304b, and a green receptacle 303g for receiving a green filter 306g (not shown) adapted to pass only green light to a corresponding green sensor 304g. Additionally, there are sensor partitions 340 between adjacent filter and sensor receptacles 303 to prevent a sensor in one receptacle, e.g. , receptacle 303b, from receiving light from filters in adjacent receptacles, e.g. , 303r or 303g. In this way, the sensor partitions eliminate cross-talk between a sensor and filters associated with adjacent receptacles. Because the sensor partitions 340 prevent 36 sensors 304 from receiving wavelengths other than their designated color wavelength, the sensors 304 generate analog outputs representative of their designated colors. Other full color cells such as cells 334b, 334c, 334d and 334e are constructed identically. As seen in FIG. 13a and 13d, cells are divided from each other by cell partitions 336 which extend between adjacent color cells 334 from the sensor end 324 to the mask end 322. These partitions ensure that each ofthe sensors 304 in a color cell 334 receives light from a common portion ofthe bill. The cell partitions 336 shield the sensors 304 of a color cell 334 from noisy light reflected from areas outside of that cell's scan area such as light from the scan area of an adjacent cell or light from areas outside the scan area of any cell. To further facilitate the viewing of a common portion of a bill by all the sensors in a color cell 334, the sensors 304 are positioned 0.655 inches from the slit 318 This distance is selected based on the countervening considerations that (a) increasing the distance reduces the intensity of light reaching the sensors and (b) decreasing the distance decreases the extent to which the sensors in a cell see the same area of a bill. Placing the light source on the document side ofthe slit 318 makes the sensors more forgiving to wrinkled bills because light can flood the document since the light is not restricted by the mask 310. Because the light does not have to pass through the slits of a mask, the light intensity is not reduced significantly when there is a slight (e.g., 0.03") wrinkle in a document as it passes under the scanhead 300. Referring to FIG. 13b, the dimensions [1, w, h] ofthe filters 306 are 0.13, 0.04, 0.23 inches and the dimensions ofthe filter receptacles 303 are 0.141 x 0.250 inches and ofthe sensors 304 are 0.174 x 0.079 x 0.151 inches. The active area of each sensor 304 is 0.105 x 0.105 inches. Each sensor generates an analog output signal representative ofthe characteristic information detected from the bill. Specifically, the analog output signals from each color cell 334 are red, blue and green analog output signals from the red, blue and green sensors 304r, 304b and 304g, respectively (see FIG. 8). These red, blue and green analog output signals are amplified by the amplifier 58 and converted into digital red, blue and green signals by means ofthe analog-to-digital converter (ADC) unit 52 whose output is fed as a digital input to the central processing unit (CPU) 54 as described above in conjunction with FIG. 1. These signals are then processed as described above to identify 37 the denomination and/or type of bill being scanned. According to one embodiment, the outputs of an edge sensor 338 and the green sensor ofthe left color cell 334a are monitored by the PROCESSOR 54 to initially detect the presence ofthe bill 44 adjacent the color scanhead 300 and, subsequently, to detect the bill edge 44b. As seen in FIG. 13a, a mask 310 having a narrow slit 318 therein covers the top ofthe scanhead. The slit 318 is 0.050 inches wide. A pair of light sources 308 illuminate a bill 44 as it passes the scanhead 300 on the transport plate 140. The illustrated light sources 308 are fluorescent tubes providing white light with a high intensity in the red, blue and green wavelengths. As mentioned above, the fluorescent tubes 308 may be part number CBY26-220NO manufactured by Stanley of Japan. These tubes have a spectrum from about 400 mm to 725 mm with peaks for blue, green and red at about 430 mm, 540mm and 612mm, respectively. As can be seen in FIG. 13f, the light from the light sources 308 passes through a transparent glass shield 314 positioned between the light sources 308 and the transport plate 140. The glass shield 314 assists in guiding passing bills flat against the transport plate 140 as the bills pass the scanhead 300. The glass shield 314 also protects the scanhead 300 from dust and contact with the bill. The glass shield 314 may be composed of, for example, soda glass or any other suitable material. Because light diffuses with distance, the scanhead 302 is designed to position the light sources 308 close to the transport path 140 to achieve a high intensity of light illumination on the bill. In one embodiment, the tops ofthe fluorescent tubes 308 are located 0.06 inches from the transport path 140. The mask 310 ofthe scanhead 300 also assists in illuminating the bill with the high intensity light. Referring to FIG. 13f, the mask 310 has a reflective surface 316 facing to the light sources 308. The reflective side 316 ofthe mask 310 directs light from the light sources 308 upwardly to illuminate the bill. The reflective side 316 ofthe mask 310 may be chrome plated or painted white to provide the necessary reflective character. The combination ofthe two fluorescent light tubes 308 and the reflective side 316 ofthe mask 310 enhances the intensity or brightness of light on the bill while keeping the heat generated within the currency handling system 10 at acceptable levels. 38 The light intensity on the bill must be sufficiently high to cause the sensors 304 to produce output signals representative ofthe characteristic information on the bill. Alternatives to the pair of fluorescent light tubes may be used, such as different types of light sources and/or additional light sources. However, the light sources should flood the area ofthe bill scanned by the scanhead 300 with high intensity light while minimizing the heat generated within the currency handling system. Adding more light sources may suffer from the disadvantages of increasing the cost and size ofthe currency handling system. Light reflected off the illuminated bill enters a manifold 312 ofthe scanhead 300 by passing through the narrow slit 318 in the mask 310. The slit 318 passes light reflected from the scan area or the portion ofthe bill directly above the slit 318 into the manifold 312. The reflective side 316 ofthe mask 310 blocks the majority of light from areas outside the scan area from entering the manifold 312. In this manner, the mask serves as a noise shield by preventing the majority of noisy light or light from outside the scan area from entering the manifold 312. In one embodiment, the slit has a width of 0.050 inch and extends along the 6.466 inch length the scanhead 300. The distance between the slit and the bill is 0.195 inch, the distance between the slit and the sensor is 0.655 inch, and the distance between the sensor and the bill is 0.85 inch. The ratio between the sensor-to-slit distance and the slit-to-bill distance is 3.359:1. By positioning the slit 318 away from the bill, the slit 318 passes light reflected from a greater area of the bill. Increasing the scan area yields outputs corresponding to an average of a larger scan area. One advantage of employing fewer samples of larger areas is that the currency handling system is able to process bills at a faster rate, such as at a rate of 1200 bills per minute. Another advantage of employing larger sample areas is that by averaging information from larger areas, the impact of small deviations in bills which may arise from, for example, normal wear and/or small extraneous markings on bills, is reduced. That is, by averaging over a larger area the sensitivity ofthe currency handling system to minor deviations or differences in color content is reduced. As a result, the currency handling system is able to accurately discriminate bills of different denominations and types even if the bills are not in perfect condition. 39 FIG. 13g illustrates the light trapping geometry ofthe manifold 312 is provided. Light reflected from the scan area 48 ofthe bill 44 travels through the slit 318 and into the manifold 312. The light passes through the manifold 312 and the filter 306 to the sensor 304. However, because the light reflected from the bill includes light reflected perpendicular to and at other angles to the bill 44, the light passing through the slit 318 includes some light reflected from areas outside the scan area 48. To prevent noisy light or light from outside the scan area 48 from being detected by the sensors 304, the manifold 312 has a light trapping geometry. By reducing the amount of noisy light received by the sensors 304, the magnitude of intensity ofthe light needed to illuminate the bill to provide accurate sensors outputs is reduced. The light trapping geometry ofthe manifold 312 reflects the majority of noisy light away from the sensors 304. To reflect "noisy" light away from the sensors 304, the walls 326 ofthe manifold 312 have a back angle α. To form the back angle, the width of the slit end 322 ofthe manifold 312 is made larger than the width ofthe sensor end 324 ofthe manifold 312. In one embodiment, the slit end 322 is 0.331 inches wide and the sensor end 324 is 0.125 inches wide to form a back angle of 10.5 degrees. Because of the light trapping geometry, the majority ofthe reflected light entering the manifold 312 that does not directly pass to the sensor 304 will be reflected off the back angled walls 326 away from the sensors 304. Furthermore, the walls 326 ofthe manifold 312 are either fabricated from or coated with a light absorbing material to prevent the noisy light from traveling to the sensors 304. Additionally, the interior surface ofthe manifold walls may be textured to further prevent the noisy light from traveling to the sensors 304. Moreover, the manifold side 328 ofthe mask 310 may be coated with a light absorbing material such as black paint and/or provided with a textured surface to prevent the trapped light rays from being reflected toward the sensor 304. The mask 310 is grounded so that it can act as an electrical noise shield. Grounding the mask 310 shields the sensors 304 from electromagnetic radiation noise emitted by the fluorescent tubes 308, thus further reducing electrical noise. As best seen in FIGS. 13c and 13d, in one embodiment, the scanhead 300 has a length L M of 7.326 inches, a height H M of 0.79 inches, and a width W M of 0.5625 inches. Each cell has a length L c of /4 inches and the scanhead has an overall interior length L j 40 of 7.138 inches. In the embodiment depicted in FIG. 13d, the scanhead 300 is populated with five full color cells 334a, 334b, 334c, 334d and 334e laterally positioned across the center ofthe length ofthe scanhead 300 and one edge sensor 338 at the left ofthe first color site 334a. See also FIG. 13b. The edge sensor 338 comprises a single sensor without a corresponding filter to detect the intensity ofthe reflected light and hence acts as a bill edge sensor. While the embodiment shown in FIG. 13d depicts an embodiment populated with five full color cells, because the body 302 ofthe scanhead 300 has sensor and filter receptacles 303 to accommodate up to forty-three filters and/or sensors, the scanhead 300 may be populated with a variety of color cell configurations located in a variety of positions along the length ofthe scanhead 300. For example, in one embodiment only one color cell 334 may be housed anywhere on the scanhead 300. In other situations up to fourteen color cells 334 may be housed along the length ofthe scanhead 300. Additionally, a number of edge sensors 338 may be located in a variety of locations along the length ofthe scanhead 300. Moreover, if all ofthe receptacles 303 were populated, it would be possible to select which color cells to use or process to scan particular bills or other documents. This selection could be made by a processor based on the position of a bill as sensed by the position sensors (FIG. 15b). This selection could also be based on the type of currency being scanned, e.g., country, denomination, series, etc., based upon an initial determination by other sensor(s) or upon appropriate operator input. According to one embodiment, the cell partitions 336 may be formed integrally with the body 302. Alternatively, the body 302 may be constructed without cell partitions, and configured such that cell partitions 336 may be accepted into the body 302 at any location between adjacent receptacles 303. Once inserted into the body 302, a cell partition 336 may become permanently attached to the body 302. Alternatively, cell partitions 336 may be removeably attachable to the body such as by being designed to snap into and out ofthe body 302. Embodiments that permit cell partitions 336 to be accepted at a number of locations provide for a very flexible color scanhead that can be readily adapted for different scanning needs such as for scanning currency bills from different countries. 41 For example, if information that facilitates distinguishing bills of different denominations from a first country such as Canada can be obtained by scanning central regions of bills, five cells such as 334a-334e can be positioned near the center ofthe scanhead as in FIG. 13b. Alternatively, if information that facilitates distinguishing bills of different denominations from a second country such as Turkey can be obtained by scanning regions near the edges of bills, cells can be positioned near the edges ofthe scanhead. In this manner, standard scanhead components can be manufactured and then assembled into various embodiments of scanheads adapted to scan bills from different countries or groups of countries based on the positioning of cell locations. Accordingly, a manufacturer can have one standard scanhead body 302 part and one standard cell partition 336 part. Then by appropriately inserting cell partitions into the body 302 and adding the appropriate filters and sensors, a scanhead dedicated to scanning a particular set of bills can be easily assembled. For example, including a single edge sensor, such as sensor 338, and only a single color cell located in the center ofthe scanhead, such as cell 334c, U.S. bills can be discriminated; Canadian bills can be discriminated if cells 334a-334e are populated and Euro currency can be discriminated using only cells 334a and 334e. Therefore, a single currency handling system employing a scanhead populated with color cells 334a-334e and edge sensor 338 can be used to process and discriminate U.S., Canadian, and Euro currency. Alternatively, a universal scanhead can be manufactured that is fully populated with cells across the entire length ofthe scanhead. For example, the scanhead 300 may comprise fourteen color cells and one edge cell. Then a single scanhead may be employed to scan many types of currency. The scanning can be controlled based on the type of currency being scanned. For example, if the operator informs the currency handling system, or the currency handling system determines, that Canadian bills are being processed, the outputs of sensors in cells 334a-334e can be processed. Alternatively, if the operator informs the currency handling system, or the currency handling system determines that Thai bills are being processed, the outputs of sensors in cells near the edges ofthe scanhead can be processed. 42 Referring to FIGS. 5a-c and 6a-g, the full color scanhead 300 forms part of a color scanhead module 581. In addition to the scanhead 300, the scanhead module 581 comprises a transport plate 540, printed circuit boards (PCB) 501 and 502, passive rolls 550 and 551, UV/fluorescence sensor 340, magnetic sensor (not shown), thread sensor (not shown), UV light source 342, fluorescent light tubes 308, color mask 310, glass shield 314, color filters 306, photosensors 304, sensor partitions 336 and other elements and circuits for processing color characteristics. Many of these parts have been described above with reference to FIGS. 13a-g. FIG. 6a is a perspective view ofthe color scanhead module 581. As seen in FIGS. 6c-6e, the module is compact in size having a length L CM of 7.6 inches, a width W CM of 4.06 inches, and a height H CM of 1.8 inches. FIGS. 6d and 6e are included only to show relative overall size ofthe module, and therefore show few details. The compact size ofthe color module contributes to a reduction the size ofthe overall currency handling system in which it is employed. As described above, reducing the size and weight ofthe overall currency handling system is desirable in many environments in which the system is to be employed. FIG. 6b is a perspective exploded view ofthe color scanhead module 581. Illustrated in FIG. 6b, from the top down, are the transparent glass shield 314, which is positioned above the light sources 308 and the mask 310 having the narrow slit 318 therein. The mask 310 covers the top of the scanhead 300 which is situated in the housing 354 ofthe color scanhead module 581. The scanhead 300 can be formed integrally with the housing 354 if desired. A first PCB 501 contains the sensors 304 (not shown in FIG. 6b) which have filters 306 that rest upon the respective sensors 304 below. Also contained on the first PCB 501, is an UV sensor 340. A second PCB 502 is disposed below the first PCB 501 and contains further circuitry for processing the data from the sensors 304. Each sensor generates an analog output signal representative ofthe characteristic information detected from the bill. The analog output signals from each color cell 334 comprises red, blue and green analog output signals from their respective red sensor 304r, blue sensor 304b and green sensor 304g. As described above in connection with FIG. 1, these red, blue and green analog output signals are amplified by the amplifier 58 and converted into digital red, blue and green signals by means ofthe analog-to-digital converter (ADC) unit 52 whose output is fed as a digital input to the central processing 43 unit (CPU) 54. These signals are then processed as described above to discriminate the denomination and/or type of bill being scanned. According to one embodiment, the outputs ofthe edge sensor 338 and the green sensor ofthe left color cell 334e are monitored by the PROCESSOR 54 to initially detect the presence ofthe bill 44 adjacent the color scanhead 300 and, subsequently, to detect the edge ofthe bill 44b as described above in connection with FIG. 8. As seen in FIG. 6a, the mask 310 having the narrow slit 318 therein covers the top ofthe scanhead. The slit 318 is 0.050 inches wide. The pair of light sources 308 illuminate a bill 44 as it passes the scanhead 300 on the transport plate 140. In one embodiment, the light sources 308 are fluorescent tubes providing white light with a high intensity in the red, blue and green wavelengths. As mentioned above, according to one embodiment the fluorescent tubes are part number CBY26-220NO manufactured by Stanley of Japan. Those florescent tubes have a spectrum from about 400 nm to 725 nm with peaks for blue, green and red at about 430 nm, 540 nm and 612 nm, respectively. As seen in FIGS. 6f-g, the light from the light sources 308 passes through the transparent glass shield 314 positioned between the light sources 308 and the transport plate 140. The glass shield 314 assists in guiding passing bills flat against the transport plate 140 as the bills pass the scanhead 300. The glass shield 314 also protects the scanhead 300 from dust and contact with the bill. The glass shield 314 may be composed of, for example, soda glass or any other suitable material. IV. OTHER SENSORS A. Magnetic In addition to the optical and color scanheads described above, the currency handling system 10 may include a magnetic scanhead. FIG. 14 illustrates a scanhead 86 having magnetic sensor 88. A variety of currency characteristics can be measured using magnetic scanning. These include detection of patterns of changes in magnetic flux (U.S. Patent No. 3,280,974), patterns of vertical grid lines in the portrait area of bills (U.S. Patent No. 3,870,629), the presence of a security thread (U.S. Patent No. 5,151,607), total amount of magnetizable material of a bill (U.S. Patent No. 4,617,458), patterns from sensing the strength of magnetic fields along a bill (U.S. Patent No. 44 4,593,184), and other patterns and counts from scanning different portions ofthe bill such as the area in which the denomination is written out (U.S. Patent No. 4,356,473). The denomination determined by optical scanning or color scanning of a bill may be used to facilitate authentication ofthe bill by magnetic scanning, using the relationships set forth in Table 1. Table 1 Sensitivity 1 2 n 4 5 Denomination $1 200 250 300 375 450 $2 100 125 150 225 300 $5 200 250 300 350 400 $10 100 125 150 200 250 $20 120 150 180 270 360 $50 200 250 300 375 450 $100 100 125 150 250 350 Table 1 depicts relative total magnetic content thresholds for various denominations of genuine bills. Columns 1 -5 represent varying degrees of sensitivity selectable by a user of a device employing the present invention. The values in Table 1 are set based on the scanning of genuine bills of varying denominations for total magnetic content and setting required thresholds based on the degree of sensitivity selected. The information in Table 1 is based on a total magnetic content of 1000 for a genuine $1. The following discussion is based on a sensitivity setting of 4. In this example it is assumed that magnetic content represents the second characteristic tested. If the comparison of first characteristic information, such as reflected light intensity or color content of reflected light, from a scanned billed and stored information corresponding to genuine bills results in an indication that the scanned bill is a $10 45 denomination, then the total magnetic content ofthe scanned bill is compared to the total magnetic content threshold of a genuine $10 bill, i.e., 200. If the magnetic content ofthe scanned bill is less than 200, the bill is rejected. Otherwise it is accepted as a $10 bill. B. Size In addition to intensity, color and magnetic scanning as described above, the currency handling system 10 may determine the size of a currency bill. The "X" size dimension of a currency bill is determined by reference to FIG. 15a and 15b which illustrate the upper standard scanhead 70 for optically sensing the size and/or position of a currency bill under test. The "Y" dimension may be determined by either of the systems shown in FIGS. 17 and 19. The scanhead 70 may be used alternatively or in addition to any ofthe other sensing systems heretofore described. The scanhead 70, like the systems of FIGS. 17 and 19, is particularly useful in foreign markets in which the size of individual bills varies with their denomination. The scanhead 70 is also useful in applications which require precise bill position information such as, for example, where a bill attribute is located on or in the bill (e.g., color, hologram, security thread, etc.). The scanhead 70 includes two photo-sensitive linear arrays 1502a, 1502b. Each of the linear arrays 1502a, 1502b consists of multiple photosensing elements (or "pixels") aligned end-to-end. The arrays 1502a, 1502b, having respective lengths Li and L 2 , are positioned such that they are co-linear and separated by a gap "G." In one embodiment, each linear array 1502a and 1502b comprises a 512-element Texas Instruments model TSL 218 array, commercially available from Texas Instruments, Inc., Dallas, Texas. In the TSL 218 arrays, each pixel represents an area of about 5 mils in length, and thus the arrays 1502a, 1502b have respective lengths Lj and L 2 of 214 inches. In one embodiment, the gap G between the arrays is about 2 inches. In this embodiment, therefore, the distance between the left end of array 1502a and the right end of array 1502b is seven inches (Lj + L 2 + G), thus providing the scanhead 70 with the ability to accommodate bills of at least seven inches in length. It will be appreciated that the scanhead 70 may be designed with a single array and/or may use array(s) having fewer or greater numbers of elements, having a variety of alternative lengths L] and L 2 and/or having a variety of gap sizes (including, for instance, a gap size of zero). 46 The operation of the scanhead 70 is best illustrated in FIGS. 5a-c. The arrays 1502a, 1502b (not visible in FIGS. 5a-c) of the upper head assembly 70 are positioned above the transport path and the lower color scanhead 300. The light source 308, which in the illustrated embodiment comprises a pair of fluorescent light tubes, is positioned below the upper head assembly 70 and the transport path. In one embodiment, the arrays 1502a, 1502b are positioned directly above one of the tubes 308. It will be appreciated that the illustrated embodiment may be applied to systems having non-horizontal (e.g., vertical) transport paths by positioning the scanhead 70 and light source 308 on opposite sides (e.g., top and bottom) ofthe transport path. The individual pixels in the arrays 1502a, 1502b are adapted to detect the presence or absence of light transmitted from the light tubes 308. In one embodiment, gradient index lens arrays 1514a, 1514b, manufactured by NSG America, Somerset, NJ, part no. SLA-20B 144-570- 1-226/236, are mounted between the light tubes 308 and the respective sensor arrays 1502a, 1502b. The gradient index lens arrays 1514a, 1514b maximize the accuracy ofthe scanhead 70 by focusing light from the light tubes 308 onto the photo-sensing elements and filtering out extraneous light and reflections, which may otherwise adversely affect the accuracy of the scanhead 70. Alternatively, less accurate but relatively reliable measurements may be obtained by replacing the gradient index lens arrays 1514a, 1514b with simpler, less expensive filters such as, for example, a plate (not shown) with aligned holes or a continuous slot allowing passage of light from the light tubes 308 to the arrays 1502a, 1502b. When no bill is present between the light tubes 308 and the arrays 1502a, 1502b, all ofthe photo-sensing elements are directly exposed to light. When a currency bill is advanced along the transport path between the light tubes 308 and the arrays 1502a, 1502b, a certain number ofthe photo-sensing elements will be blocked from light. The number of elements or "pixels" blocked from light will determine the length ofthe bill. Specifically, in one embodiment, the size ofthe long dimension ofthe bill is determined by the circuit of FIG. 16. There, two photosensor arrays 1600 (which may be the arrays 1502a, 1502b) are connected to two comparators 1602. Each photosensor array 1600 is enabled by a start pulse from a Programmable Logic Device (PLD) 1604. The clock pin (CLK) of each array 1600 is electrically connected to the CLK inputs of right and left 47 counters, 1606 and 1608, in the PLD 1604. Each comparator 1602 is also electrically connected to a source of a reference signal. The output of each comparator 1602 is electrically connected to the enable (EN) inputs ofthe counters 1606 and 1608. The PLD 1604 is controlled by the PROCESSOR 54. The circuit of FIG. 16 is asynchronous. The size of a bill is determined by sampling the outputs ofthe counters 1606 and 1608 after the leading edge ofthe bill is approximately one inch past the arrays 1502a, 1502b. The counters 1606 and 1608 count the number of uncovered pixels. The long dimension ofthe bill is determined by subtracting the number of uncovered pixels in each array from 511 (there are 512 pixels in each array 1600, and the counters 1606 and 1608 count from 0 to 511 ). The result is the number of covered pixels, each of which has a length of 5 mils. Thus, the number of covered pixels times 5 mils, plus the length of the gap G, gives the length ofthe bill. The system 10 also provides bill position information and fold/hole fitness information by using the "X" dimension sensors. These sensors can detect the presence of one or more holes in a document by detecting light passing through the document. And, as described more fully below, these sensors can also be used to measure the light transmittance characteristics ofthe document to detect folded documents and/or documents that are overlapped. The "Y" dimension is determined by the optical sensing system of FIG. 17, which determines the Y dimension of a currency bill under test. This size detection system includes a light emitter 1762 which sends a light signal 1764 toward a light sensor 1766. In one embodiment, the sensor 1766 corresponds to sensors 95 and 97 illustrated in FIG. 15. The sensor 1766 produces a signal which is amplified by amplifier 1768 to produce a signal Vi proportional to the amount of light passing between the emitter and sensor. A currency bill 1770 is advanced across the optical path between the light emitter 1762 and light sensor 1766, causing a variation in the intensity of light received by the sensor 1766. As will be appreciated, the bill 1770 may be advanced across the optical path along its longer dimension or narrow dimension, depending on whether it is desired to measure the length or width ofthe bill. Referring to the timing diagram of FIG. 18, at time t l5 before the bill 1770 has begun to cross the path between the light emitter 1762 and sensor 1766, the amplified 48 sensor signal Vj is proportional to the maximum intensity of light received by the sensor 1766. The signal V, is digitized by an analog-to-digital converter and provided to the processor 1712, which divides it by two to define a value Vι/2 equal to one-half of the maximum value of Vi. The value Vι/2 is supplied to a digital-to-analog converter 1769 to produce an analog signal V 3 which is supplied as a reference signal to a comparator 1774. The other input to the comparator 1774 is the amplified sensor signal V] which represents the varying intensity of light received by the sensor 1766 as the bill 1770 crosses the path between the emitter 1762 and sensor 1766. In the comparator 1774, the varying sensor signal V] is compared to the reference signal V 3 , and an output signal is provided to an interrupt device whenever the varying sensor signal V] falls above or below the reference V 3 . Alternatively, the system could poll the sensors periodically, for example, every 1 ms. As can be seen more clearly in the timing diagram of FIG. 18, the interrupt device produces a pulse 1976 beginning at time t 2 (when the varying sensor signal V ! falls below the V 3 reference) and ending at time t 3 (when the varying sensor signal V ! rises above the V 3 reference). The length of the pulse 1976 occurring between times t 2 and t 3 is computed by the processor 1712 with reference to a series of timer pulses from the encoder. More specifically, at time t 2 , the processor 1712 begins to count the number of timer pulses received from the encoder, and at time t 3 the processor stops counting. The number of encoder pulses counted during the interval from time t 2 to time t 3 represents the width ofthe bill 1770 (if fed along its narrow dimension) or length of the bill 1770 (if fed along its longer dimension). It has been found that light intensity and/or sensor sensitivity will typically degrade throughout the life ofthe light emitter 1762 and the light sensor 1766, causing the amplified sensor signal V[ to become attenuated over time. The signal Vi can be further attenuated by dust accumulation on the emitter or sensor. One ofthe advantages ofthe above-described size detection method is that it is independent of such variations in light intensity or sensor sensitivity. This is because the comparator reference V 3 is not a fixed value, but rather is logically related to the maximum value of Nj. When the maximum value of V] attenuates due to degradation ofthe light source, dust accumulation, etc., V 3 is correspondingly attenuated because its value is always equal to 49 one-half of the maximum value of V,. Consequently, the width ofthe pulse derived from the comparator output with respect to a fixed length bill will remain consistent throughout the life ofthe system, independent ofthe degradation ofthe light source 1762 and sensor 1766. FIG. 19 portrays an alternative circuit which may be used to detect the Y dimension of a currency bill under test. In FIG. 19, the method of size detection is substantially similar to that described in relation to FIG. 17 except that it uses analog rather than digital signals as an input to the comparator 1974. A diode Dl is connected at one end to the output ofthe amplifier 68 and at another end to a capacitor Cl connected to ground. A resistor Rl is connected at one end between the diode Dl and the capacitor Cl . The other end ofthe resistor Rl is connected to a resistor R2 in parallel with the reference input 1978 ofthe comparator 1974. If Rl and R2 are equal, the output voltage V 3 on the reference input 1978 will be one-half of the peak voltage output from the amplifier 1908. In the comparator 1974, the varying sensor signal V ! is compared to the output voltage V 3 , and an output signal is provided to an interrupt device whenever the varying sensor signal Vi falls above or below the V 3 reference. Thereafter, a pulse 1976 is produced by the interrupt device, and the length ofthe pulse 1976 is determined by the processor 1912 in the same manner described above. In the circuit of FIG. 19, as in the circuit of FIG. 17, the signal V 2 is proportional to V and the widths of pulses derived from the comparator output are independent ofthe degradation ofthe light source 1902 and sensor 1906. C. Fold/Hole Detection As mentioned above, in addition to detecting the size ofthe currency bills, the currency handling system 10 may include a system for detecting folded or damaged bills as illustrated in FIG. 20. The two photosensors PSI and PS2 are used to detect the presence of a folded document or the presence of a document having hole(s) therein, by measuring the light transmittance characteristics ofthe document(s). Folds and holes are detected by the photosensors PSI and PS2, such as the "X" sensors 1502a,b, which are located on a common transverse axis that is perpendicular to the direction of bill flow. The photosensors PSI and PS2 include a plurality of photosensing elements or pixels positioned directly opposite a pair of light sources on the other side ofthe bill, such as 50 the light sources 308 ofthe color scanhead illustrated in FIG. 13a. The "X" sensors detect whether a pixel is covered or exposed to light from the light sources 308. The output ofthe photosensors determines the presence of folded bills and/or damaged bills such as bills missing a portion ofthe bill. For example, by using the "X" sensors, a folded bill can be detected in either of two ways. The first way is to store the size of an authentic bill and then detect the size ofthe bill being processed by counting the number of blocked pixels. If the size is less than the stored size, the system determines that the bill is folded. The second way is to detect the amount of light transmitted through the bill to determine the extent ofthe fold and where the fold stops. Using the second method, the size ofthe bill can be determined. D. Doubles Detection Doubling or overlapping of bills is detected by the photosensors PSI and PS2. such as the "Y" sensors 95, 97, which are located on a common transverse axis that is perpendicular to the direction of bill flow. The photosensors PSI and PS2 are positioned directly opposite a pair of light sources on the other side ofthe bill, such as the light sources 308 ofthe color scanhead illustrated in FIG. 13a. The photosensors PSI and PS2 detect transmitted light from the light sources 308 and generate analog outputs which correspond to the sensed light that passes through the bill. Each such output is converted into a digital signal by a conventional ADC converter unit 52 whose output is fed as a digital input to and processed by the system PROCESSOR 54. The presence of a bill adjacent the photosensors PSI and PS2 causes a change in the intensity ofthe detected light, and the corresponding changes in the analog outputs of the photosensors PSI and PS2 serve as a convenient means for density-based measurements for detecting the presence of "doubles" (two or more overlaid or overlapped bills) encountered during the currency scanning process. For instance, the photosensors may be used to collect a predefined number of density measurements on a test bill, and the average density value for a bill may be compared to predetermined density thresholds (based, for instance, on standardized density readings for master bills) to determine the presence of overlaid bills or doubles. 51 E. Normalization In one embodiment, the currency handling system 10 monitors the intensity of light provided by the light sources. It has been found that the light source and/or sensors of a particular system may degrade over time. Additionally, the light source and/or sensor of any particular system may be affected by dust, temperature, imperfections, scratches, or anything that may affect the brightness ofthe tubes or the sensitivity ofthe sensor. Similarly, systems utilizing magnetic sensors will also generally degrade over time and/or be affected by its physical environment including dust, temperature, etc. To compensate for these changes, each currency handling system 10 will typically have a measurement "bias" unique to that system caused by the state of degradation ofthe light sources or sensors associated with each individual system. The present invention is designed to achieve a substantially consistent evaluation of bills between systems by "normalizing" the master information and test data to account for differences in sensors between systems. For example, where the master information and the test data comprise numerical values, this is accomplished by dividing both the threshold data and the test data obtained from each system by a reference value corresponding to the measurement of a common reference by each respective system. The common reference may comprise, for example, an object such as a mirror or piece of paper or plastic that is present in each system. The reference value is obtained in each respective system by scanning the common reference with respect to a selected attribute such as size, color content, brightness, intensity pattern, etc. The master information and/or test data obtained from each individual system is then divided by the appropriate reference value to define normalized master information and/or test data corresponding to each system. The evaluation of bills in the standard mode may thereafter be accomplished by comparing the normalized test data to normalized master information. F. Attributes Sensed The characteristic information obtained from the scanned bill may comprise a collection of data values each of which is associated with a particular attribute ofthe bill. The attributes of a bill for which data may be obtained by magnetic sensing include, for example, patterns of changes in magnetic flux (U.S. Patent No. 3,280,974), patterns of 52 vertical grid lines in the portrait area of bills (U.S. Patent No. 3,870,629), the presence of a security thread (U.S. Patent No. 5,151,607), total amount of magnetizable material of a bill (U.S. Patent No. 4,617,458), patterns from sensing the strength of magnetic fields along a bill (U.S. Patent No. 4,593,184), and other patterns and counts from scanning different portions ofthe bill such as the area in which the denomination is written out (U.S. Patent No. 4,356,473). The attributes of a bill for which data may be obtained by optical sensing include, for example, density (U.S. Patent No. 4,381,447), color (U.S. Patent Nos. 4,490,846; 3,496,370; 3,480,785), length and thickness (U.S. Patent No. 4,255,651), the presence of a security thread (U.S. Patent No. 5,151,607) and holes (U.S. Patent No. 4,381,447), reflected or transmitted intensity levels of UV light (U.S. Patent No. 5,640,463) and other patterns of reflectance and transmission (U.S. Patent No. 3,496,370; 3.679,314; 3,870,629; 4,179,685). Color detection techniques may employ color filters, colored lamps, and/or dichroic beamsplitters (U.S. Patent Nos. 4,841,358; 4,658,289; 4,716,456; 4,825,246, 4,992,860 and EP 325,364). In addition to magnetic and optical sensing, other techniques of gathering test data from currency include electrical conductivity sensing, capacitive sensing (U.S. Patent No. 5,122,754 [watermark, security thread]; 3,764,899 [thickness]; 3,815,021 [dielectric properties]; 5,151,607 [security thread]), and mechanical sensing (U.S. Patent No. 4,381,447 [limpness]; 4,255,651 [thickness]). Each ofthe aforementioned patents relating to optical, magnetic or alternative types of sensing is incorporated herein by reference in its entirety. V. STANDARD MODE/LEARN MODE The currency handling system 10 of FIG. 1 may be operated in either a "standard" currency evaluation mode or a "learn" mode. In the standard currency evaluation mode, the data obtained by the scanheads or sensors 70, is compared by the PROCESSOR 54 to prestored master information in the memory 56. The prestored master information corresponds to data generated from genuine "master" currency of a plurality of denominations and/or types. Typically, the prestored data represents an expected numerical value or range of numerical values or a pattern associated with the characteristic information scan of genuine currency. The prestored data may further 53 represent various orientations and/or facing positions of genuine currency to account for the possibility of a bill in the stack being in a reversed orientation or reversed facing position compared to other bills in the stack. The specific denominations and types of currency from which master information may be expected to be obtained for any particular system 10 will generally depend on the market in which the system 10 is used (or intended to be used). In European market countries, for example, with the advent of Euro currency (EC currency), it may be expected that both EC currency and a national currency will circulate in any given country. In Germany, for a more specific example, it may be expected that both EC currency and German deutsche marks (DMs) will circulate. With the learn mode capability ofthe present invention, a German operator may obtain master information associated with both EC and DM currency and store the information in the memory 56. Of course, the "family" of desirable currencies for any particular system 10 or market may include more than two types of currencies. For example, a centralized commercial bank in the European community may handle several types of currencies including EC currency, German DMs, British Pounds, French Francs, U.S. Dollars, Japanese Yen and Swiss Francs. In like manner, the desirable "family" of currencies in Tokyo, Hong Kong or other parts of Asia may include Japanese Yen, Chinese Remimbi, U.S. Dollars, German DMs, British Pounds and Hong Kong Dollars. As a further example, a desirable family of currencies in the United States may include the combination of U.S. Dollars, British Pounds, German DMs, Canadian Dollars and Japanese Yen. With the learn mode capability ofthe present invention, master information may be obtained from any denomination of currency in any desired "family" by simply repeating the learn mode for each denomination and type of currency in the family. This may be achieved in successive operations ofthe learn mode by running currency bills ofthe designated family, one currency denomination and type at a time, through the scanning system 10 to obtain the necessary master information. The number of bills fed through the system may be as few as one bill, or may be several bills. The bill(s) fed through the system may include good quality bill(s), poor quality bills or both. The master information obtained from the bills defines ranges of acceptability for 54 patterns of bills ofthe designated denomination and type which are later to be evaluated in "standard" mode. For example, suppose a single good quality bill of a designated denomination and type is fed through the system 10 in the learn mode. The master information obtained from the bill may be processed to define a range of acceptability for bills ofthe designated denomination and type. For instance, the master information obtained from the learn mode bill may define a "center" value ofthe range, with "deltas," plus or minus the center value, being determined by the system 10 to define the upper and lower bounds ofthe range. Alternatively, a range of acceptability may be obtained by feeding a group of bills through the system 10 one at a time, each bill in the group being of generally "good" quality, but differing in degree of quality from others in the group. In this example, the average value ofthe notes in the group may define a "center value" of a range, with values plus or minus the center value defining the upper and lower bounds of the range, as described above. Alternatively, master information obtained from the poorest quality of the learn mode or master bills may be used to define the limits of acceptability for bills ofthe designated denomination and type, such that bills ofthe designated denomination and type evaluated in the standard mode will be accepted if they are at least as "good" in quality as the poorest quality ofthe learn mode or master bills. Still another alternative is to feed one or more poor quality bills through the system 10 to define "unacceptable" bill(s) ofthe denomination and type, such that bills ofthe designated denomination and type evaluated in standard mode will not be accepted unless they are better in quality than the poor quality learn mode bills. Because the currency bills are initially unrecognizable to the currency handling system 10 in the learn mode, the operator must inform the system 10 (by means of operator interface panel 32 or external signal, for example) which denomination and type of currency it is "learning," so that the system 10 may correlate the master information it obtains (and stores in memory) with the appropriate denomination, type and "acceptability" ofthe bill(s). For purposes of illustration, suppose that an operator desires to obtain master information for $5 and $10 denominations of U.S. and Canadian Dollars. In one 55 embodiment, this may be achieved by instructing the system 10, by means of an operator interface panel 32 or external signal, to enter the learn mode and that it will be reading a first denomination and type of currency (e.g., $5 denominations of U.S. currency). In one embodiment, the operator may further instruct the system 10 which type of learn mode sensor(s) it should use to obtain the master information and/or what type of characteristic information it should obtain to use as master information. The operator may then insert a single good-quality $5 dollar U.S. bill (or a number of such bills) in the hopper 36 and feed the bill(s) through the system to obtain master information from the bill(s) from a designated combination of learn mode sensors. In an alternate embodiment, where a single bill is fed through the system 10, suppose that an arbitrary value "x" is obtained from the learn mode sensors. The system 10 may define the value "x" to be a center value of an "acceptable" range for $5 dollar U.S. bills. The system 10 may further define the values "1.2x" and "0.8x" to comprise the upper and lower bounds ofthe "acceptable" range for $5 dollar U.S. bills. Alternatively, where multiple $5 dollar U.S. bills, each bill being of generally "good" quality, are fed through the system 10, (and again using the arbitrary sensor value "x" for purposes of illustration), suppose that the average sensor value obtained from the bills is "l.lx". The system 10 in this case may define the "acceptable" range for $5 dollar U.S. bills to be centered at the average sensor value "l.lx," with the values "1.3x" and "0.9x" defining the respective upper and lower bounds ofthe range. Alternatively, where multiple $5 dollar U.S. bills are fed through the system 10, suppose that sensor values obtained in the learn mode range between "1.4x" and "0.9x". The system 10 may define the values "1.4x" and "0.9x" to be the upper and lower bounds ofthe "acceptable range" for $5 dollar U.S. bills, without regard to the average value. As still another example, suppose that the operator feeds two poor quality U.S. $5 dollar bills through the system 10, and suppose that sensor readings of "1.5x" and "0.7x" are obtained from the poor quality bills. The system 10 may then determine the range of acceptability for U.S. $5 dollar bills to be between the values of "0.7x" and "1.5x." Next, after master information has been obtained from U.S. $5 dollar bills, the operator feeds the next bill(s) through the system 10, and the system scans the bills to obtain master information from the bills, in any ofthe manners heretofore described. In 56 one embodiment, the operator may instruct the system 10 which type of learn mode sensor(s) it should use to obtain the master information. Alternatively, the operator may instruct the system 10 which type of master information is desired, and the system 10 automatically chooses the appropriate learn mode sensor(s). For example, an operator may wish to use optical and magnetic sensors for U.S. currency and optical sensors for Canadian currency. After the operator has obtained master information from each desired currency denomination and type, the operator instructs the system 10 to enter the "standard" mode, or to depart the "learn" mode. The operator may nevertheless re-enter the learn mode at a subsequent time to obtain master information from other currency denominations, types and/or series. It will be appreciated that the sensors used to obtain master information in the learn mode may be either separate from or the same as the sensors used to obtain data in the standard mode. Not only can the currency handling system 10 in the learn mode add master information of new currency denominations, but the system 10 may also replace existing currency denominations. If a country replaces an existing currency denomination with a new bill type for that denomination, the currency handling system 10 may learn the new bill's characteristic information and replace the previous master information with new master information. For example, the operator may use the operator interface 32 to enter the specific currency denomination to be replaced. Then, the master currency bills ofthe new bill type may be conveyed through the currency handling system 10 and scanned to obtain master information associated with the new bill's characteristic information, which may then be stored in the memory 56. Additionally, the operator may delete an existing currency denomination stored in the memory 56 through the operator interface 32. In one embodiment, the operator must enter a security code to access the learn mode. The security code ensures that qualified operators may add, replace or delete master information in the learn mode. One embodiment of how the learn mode functions is set forth in the flow chart illustrated in FIG. 21. First the operator enters the learn screen at step 2100 by pressing a key, such as a "MODE" key, on the operator interface panel 32. Next the operator 57 chooses the currency type ofthe bills to be processed in the learn mode at step 2102 by scrolling through the list of currency types that are displayed on the screen when the learn mode is entered at step 2100. The operator chooses the desired currency type by aligning the cursor with the desired currency type displayed on the screen and pressing a key such as the "MODE" key. The operator then chooses the currency symbol associated with the currency type to be processed at step 2103 by scrolling through the list of currency symbols displayed on the screen after the currency type has been chosen. The operator chooses the desired currency symbol by again aligning the cursor with the desired symbol displayed on the screen and pressing the "MODE" key. This advances the program to step 2104 where the operator enters the bill number, which is used to identify the different denomination or series of a bill for any given currency type. For example, different types of currency have denominations that have more than one series, e.g., there are two series of U.S. $100 bills, one with the old design and one with the new design. In this embodiment ofthe system 10, up to nine bill denominations and/or series can be learned. Here again, the display contains a menu of the available bill numbers (1-9), and the operator selects the desired bill number by aligning the cursor with the desired bill number and pressing the "MODE" key. Next, at step 2106, the operator enters the orientation ofthe bill, i.e., face up bottom edge forward, face up top edge forward, face down bottom edge forward or face down top edge forward. From the above selections, the system 10 determines what master information to learn from the bill(s) to be processed in the learn mode. Then, the operator in step 2110 enters the bill denomination either by scrolling through a displayed menu ofthe denominations corresponding to the currency type entered in step 2102, or in an alternate embodiment, by pressing one ofthe denomination keys to identify the particular denomination to be learned. The system 10 automatically changes the denomination associated with the denomination keys to correspond to the denominations available for the currency type entered in step 2102. When the operator enters the denomination, the system 10 advances to step 2114 where the system processes the sample bills and displays the number of sample bills to be averaged. This step is described in further detail in connection with FIG. 22. For example, it may be desirable to average several 58 different bills ofthe same denomination, but in different conditions, e.g., different degrees of wear, so that the patterns of a variety of bills ofthe same denomination, but of different conditions, can be averaged. Up to nine bills can be averaged to create a master pattern in this embodiment ofthe system 10. Typically, however, only one bill needs to be processed to generate master pattern data sufficient to authenticate a particular currency type and denomination in standard mode. This pattern averaging procedure is described in more detail in U.S. Patent No. 5,633,949. At step 2114, the system prompts the operator via the screen display to load the sample bill into the input hopper and then press a key, such as a "START" key. The bill is processed by the system 10 by being fed into the transport mechanism ofthe system 10. As the bill is fed through the system 10, the system scans the bill and adds the new information to the master pattern data corresponding to the scanned bill, as described in more detail in connection with FIG. 23. Eventually, the master pattern data will be averaged. The operator is prompted at step 2116 to save the data corresponding to the characteristics learned. The operator saves the data corresponding to the characteristics learned as a master pattern by selecting "YES" from the display menu by aligning the cursor at "YES" and pressing a key such as the "MODE" key. Similarly, to continue without storing the data, the operator selects "NO" from the display menu by aligning the cursor over "NO" and pressing the "MODE" key. An operator may decide not to save the data if, while learning one denomination, the operator decides to learn another currency denomination and/or type. If the operator saves the data, the operator will next decide whether to save the data as left, center or right master data. These positions refer to where in relation to the edges ofthe input hopper 36 the bill was located when it entered the transport mechanism 38. The system 10 has an adjustable hopper 36 so if bills of one denomination are being processed, all the bills are fed down the center ofthe transport mechanism. However, if mixed denominations are being processed in the standard mode from a currency type that had different size denominations, then the hopper would have to be adjusted to accommodate the maximum size bill in the stack. Thus, a narrower dimension bill could shift in the hopper such that the data scanned from the bill would vary according to where in the hopper the bill entered the transport 59 mechanism. Accordingly, in learn mode, master data scanned from a bill varies according to where in the input hopper the bill enters the transport mechanism. Therefore, the lateral position ofthe bill may either be communicated to the system 10 so the learned data can be stored in an appropriate memory location corresponding to the lateral position ofthe bill, or the system 10 can automatically determine the lateral position ofthe bill by use ofthe "X" sensors 1502a,b. In step 2120, the operator is prompted regarding whether or not another pattern is to be learned. If the operator decides to have the system 10 learn another pattern, the operator selects "YES" from the display menu by aligning the cursor at "YES". If another pattern is to be learned, steps 2104-2120 are repeated. If the operator chooses not to learn another characteristic by selecting "NO", then the system 10 in step 2122 will exit the learn screen. Thereafter, the operator may learn another set of currency denominations from another country by re-entering the learn screen at step 2100. The details of how the system 10 processes the sample bills in step 2114 is illustrated in the flow chart of FIG. 22. For each data sample for each pattern to be learned, the system 10 in step 2200 conditions the sensors. Four equations are used in adjusting the sensors. The first equation is the drift light intensity equation: DRIFT = (SRSR/CRSR) The light intensity drift (drift) is calculated by dividing a stored reference sensor reading SRSR by the current reference sensor reading. The stored reference sensor reading corresponds to the signal produced by the light intensity reference sensor at calibration time. The reference sensor 350 is illustrated in FIG. 13b. The adjusted red (r) or red hue, the adjusted blue (b) or blue hue and the adjusted green (g) or green hue are calculated from the following formulas: r = { [RSR - OAOV](DRIFT) - (VD)}(GM) b = {[BSR - OAOV](DRIFT) - (VD)}(GM) g = {[GSR - OAOV](DRIFT) - (VD)}(GM) The sensor readings RSR, BSR and GSR are measured in millivolts (mv). OAOV is the op-amp offset voltage which is an empirically derived error voltage obtained by reading the sensors with the fluorescent light tubes turned off and is typically between 50 mv and 1,000 mv. Drift indicates the change in light intensity. VD (dark voltage) which represents internal light reflections is obtained by reading the sensors with the 60 fluorescent light tubes on when a non-reflective black calibration standard material is placed in front ofthe sensors. The gain multiplier (GM) is an empirically derived constant obtained at calibration time from the following equation: GM - W/(WSR-OAOV) where WSR is a variable corresponding to the white sensor reading, i.e., the voltage measured when a white calibration standard is present in front ofthe sensors. OAOV is the op-amp offset voltage, and W is a constant corresponding to the voltage that the sensors should give when a white calibration standard is present in front ofthe sensors (generally, W = 2.5v). In step 2202, the system 10 takes data samples for the bill currently being scanned. For example, 64 data samples can be taken at various points along a bill. In step 2204, each data sample is added to the previously taken corresponding data sample (or to zero if this is the first bill processed). For example, if 64 data samples are taken, each ofthe 64 data samples is added to the respective data sample(s) previously taken and stored in memory. In step 2206, the operator is prompted regarding whether or not to process another bill to create the master pattern data. If the operator decides to process another bill, the operator selects "YES" from the display menu by aligning the cursor at "YES" and pressing the "MODE" key. If another bill ofthe same currency type and denomination is to be processed (for pattern averaging purposes), steps 2200-2206 are repeated. If the operator chooses not to process another bill by selecting "NO", then the system 10 proceeds to step 2208 where the averages ofthe summed data samples are computed. The average is computed by taking each sum from step 2204 and dividing by the number of bills processed. For example, if 64 data samples were taken from three bills, the sum of each ofthe 64 data samples is divided by three. Next, the system 10 determines the color percentages in step 2212. Three equations are used to determine the color percentages, namely: R = [r/(r + g + b)]-100 G = [g/(r + g + b)]-100 B = [b/(r + g + b)]-100 The first equation determines the percentage of red reflected from the bill. This is calculated by dividing the adjusted red value r by the sum ofthe adjusted red. green and 61 blue values r, g and b from step 2200 and multiplying that result by 100. The percentage of green and blue is found in a similar manner from the second and third equations, respectively. Simultaneously, the system 10 normalizes the brightness data in step 2210. The brightness data corresponds to the intensity ofthe light reflected from the bill. The equation used to normalize the brightness data is: BRIGHTNESS = [(r + g + b)/3W]-100 In that equation, W is the same as defined above. Then, the system 10 in step 2214 determines the "X" (or long) dimension ofthe bill. The system 10 then determines in step 2216 the "Y" (or narrow) dimension ofthe bill. The details of how the bill size is determined were detailed above in section B. Size. VI. BRIGHTNESS CORRELATION TECHNIQUE The result of using the normalizing equations above is that, subsequent to the normalizing process, a relationship of correlation exists between a test brightness pattern and a master brightness pattern such that the aggregate sum of the products of corresponding samples in a test brightness pattern and any master brightness pattern, when divided by the total number of samples, equals unity if the patterns are identical. Otherwise, a value less than unity is obtained. Accordingly, the correlation number or factor resulting from the comparison of normalized samples, within a test brightness pattern, to those of a stored master brightness pattern provides a clear indication of the degree of similarity or correlation between the two patterns. Accordingly a correlation number, C, for each test/master pattern comparison can be calculated using the following formula: ^_j .m Α~mι c = - wherein X ni is an individual normalized test sample of a test pattern, X mi is a master sample of a master pattern, and n is the number of samples in the patterns. According to one embodiment of this invention, the fixed number of brightness samples, n, which are digitized and normalized for a test bill scan is selected to be 64. It has experimentally been found that the use of higher binary orders of samples (such as 128, 256, etc.) does 62 not provide a correspondingly increased discrimination efficiency relative to the increased processing time involved in implementing the above-described correlation procedure. It has also been found that the use of a binary order of samples lower than 64, such as 32, produces a substantial drop in discrimination efficiency. The correlation factor can be represented conveniently in binary terms for ease of correlation. In a one embodiment, for instance, the factor of unity which results when a hundred percent correlation exists is represented in terms ofthe binary number 2 10 , which is equal to a decimal value of 1024. Using the above procedure, the normalized samples within a test pattern are compared to the master characteristic patterns stored within the system memory in order to determine the particular stored pattern to which the test pattern corresponds most closely by identifying the comparison which yields a correlation number closest to 1024. The correlation procedure is adapted to identify the two highest correlation numbers resulting from the comparison ofthe test brightness pattern to one ofthe stored master brightness patterns. At that point, a minimum threshold of correlation is required to be satisfied by these two correlation numbers. It has experimentally been found that a correlation number of about 850 serves as a good cut-off threshold above which positive calls may be made with a high degree of confidence and below which the designation of a test pattern as corresponding to any ofthe stored patterns is uncertain. As a second thresholding level, a minimum separation is prescribed between the two highest correlation numbers before making a call. This ensures that a positive call is made only when a test pattern does not correspond, within a given range of correlation, to more than one stored master pattern. Preferably, the minimum separation between correlation numbers is set to be 150 when the highest correlation number is between 800 and 850. When the highest correlation number is below 800, no positive identification can be made. In some cases a bi-level threshold of correlation is required to be satisfied before a particular call is made. The correlation procedure is adapted to identify the two highest correlation numbers resulting from the comparison ofthe test pattern to one ofthe stored patterns. A minimum threshold of correlation is required to make a positive call. It has experimentally been found that a correlation number of about 850 serves as a good cut- 63 off threshold above which positive calls may be made with a high degree of confidence and below which the designation of a test pattern as corresponding to any ofthe stored patterns is uncertain. As a second threshold level, a minimum separation is prescribed between the two highest correlation numbers before making a call. This ensures that a positive call is made only when a test pattern does not correspond, within a given range of correlation, to more than one stored master pattern. Preferably, the minimum separation between correlation numbers is set to be 150 when the highest correlation number is between 800 and 850. When the highest correlation number is below 800, no call is made. If the PROCESSOR 54 determines that the scanned bill matches one ofthe master sample sets, the PROCESSOR 54 makes a "positive" call having identified the scanned currency. If a "positive" call can not be made for a scanned bill, an error signal is generated. VII. COLOR CORRELATION TECHNIQUE One embodiment of how the system 10, in standard mode, compares and discriminates a bill is set forth in the flow chart illustrated in FIGS. 23a-23d. A bill is first scanned in standard mode by 3 ofthe 5 scanheads and the standard scanhead in step 2300. The three scanheads are located at various positions along the width ofthe bill transport path so as to scan various areas ofthe bill being processed. The system 10 next determines in step 2305 the lateral position ofthe bill in relation to the bill transport path by using the "X" sensors. In step 2310, initializing takes place, where the best and second best correlation results (from previous correlations at step 2360, if any), referred to as the "#1 and #2 answers" are initialized to zero. The system 10 determines, in step 2315, whether the size ofthe bill being processed (the test bill) is within the range ofthe master size data corresponding to one denomination of bill for the country selected. If the size is not within the range, the system 10 proceeds to point B. If the system 10 determines in step 2315 that the size ofthe test bill is within the range ofthe master size data, the system proceeds to step 2320, where the system points to a first orientation color pattern. Next, the system 10, in step 2325, computes the absolute percentage difference between the test pattern and the master pattern on a point by point basis. For example, where 64 sample points are taken along the test bill to form the test pattern, the absolute 64 percentage differences between each ofthe 64 sample points from the test bill and the corresponding 64 points from the master pattern are computed by the PROCESSOR 54. Then, the system 10 in step 2335 sums the absolute percentage differences from step 2330 for each ofthe master patterns stored in memory. In an alternative embodiment, the red and green color master patterns are usually stored in memory because the third primary color, blue, is redundant, since the sum of the percentages ofthe three primary colors must equal 100%). Thus, by storing two of these percentages, the third percentage can be derived. Thus, in an alternate embodiment, each color cell 334 could include only two color sensors and two filters. Thus, in this context, "full color sensor" could also refer to a system which employs sensors for two primary colors, and a processor capable of deriving the percentage ofthe third primary color from the percentages ofthe two primary colors for which sensors are provided. The system 10 in step 2340 proceeds by summing the result ofthe red and green sums from step 2335. The total from step 2340 is compared with a threshold value at step 2350. The threshold value is empirically derived and corresponds to a value that produces an acceptable degree of error between making a good call and making a miscall. If the total from step 2340 is not less than the threshold value, then the system proceeds to step 2365 (point D) and points to the next orientation pattern, if all orientation patterns have not been completed (step 2370) the system returns to step 2330 and the total from step 2340 is compared to the next master color pattern corresponding to the bill position determination made in step 2305. The system 10 again determines, in step 2350, whether the total from step 2340 is less than the threshold value. This loop proceeds until the total is found to be less than the threshold. Then, the system 10 proceeds to step 2360 (point C). At step 2360, the test bill brightness or intensity pattern is correlated with the first master brightness pattern that corresponds to the bill position determination made in step 2305. The correlation between the test pattern and the master pattern for brightness is computed in the manner described above under "Brightness Correlation Technique." Then, in step 2370 the system determines whether all orientation patterns have been 65 used. If not, the system returns to step 2330 (point E). If so, the system proceeds to step 2375. In step 2375, the process proceeds by pointing to the next master bill pattern in memory. The brightness patterns may include several shifted versions ofthe same master pattern because the degree of correlation between a test pattern and a master pattern may be negatively impacted if the two patterns are not properly aligned with each other. Misalignment between patterns may result from a number of factors. For example, if a system is designed so that the scanning process is initiated in response to the detection of the thin borderline surrounding U.S. currency or the detection of some other printed indicia such as the edge of printed indicia on a bill, stray marks may cause initiation of the scanning process at an improper time. This is especially true for stray marks in the area between the edge of a bill and the edge ofthe printed indicia on the bill. Such stray marks may cause the scanning process to be initiated too soon, resulting in a scanned pattern which leads a corresponding master pattern. Alternatively, where the detection of the edge of a bill is used to trigger the scanning process, misalignment between patterns may result from variances between the location of printed indicia on a bill relative to the edges of a bill. Such variances may result from tolerances permitted during the printing and/or cutting processes in the manufacture of currency. For example, it has been found that location ofthe leading edge of printed indicia on Canadian currency relative to the edge of Canadian currency may vary up to approximately 0.2 inches (approximately 014 cm). Accordingly, the problems associated with misaligned patterns are overcome by shifting data in memory by dropping the last data sample of a master pattern and substituting a zero in front ofthe first data sample ofthe master pattern. In this way, the master pattern is shifted in memory and a slightly different portion ofthe master pattern is compared to the test pattern. This process may be repeated, up to a predetermined number of times, until a sufficiently high correlation is obtained between the master pattern and the test pattern so as to permit the identity of a test bill to be called. For example, the master pattern may be shifted three times to accommodate a test bill that has its identifying characteristic(s) shifted 0.2 inches from the leading edge of 66 the bill. To do this, three zeros are inserted in front ofthe first data sample ofthe master pattern. One embodiment ofthe pattern shifting technique described above is disclosed in U.S. Patent No. 5,724,438 entitled "Method of Generating Modified Patterns and Method and Apparatus for Using the Same in a Currency Identification System," which is incorporated herein by reference. Returning to the flow chart at FIG. 23b, the system 10 in step 2380 determines whether all ofthe master bill patterns have been used. If not the process returns to step 2315 (point A). If so, the process proceeds to step 2395 (point F - see FIG. 23c). The best two correlations are determined by a simple correlation procedure that processes digitized reflectance values into a form which is conveniently and accurately compared to corresponding values pre-stored in an identical format. This is detailed above in the sections on Normalizing Technique and Correlation Technique for the Brightness Samples. Referring to FIGS. 23c-d, the system 10 determines, in step 2395, whether all the sensors have been checked. If the master patterns for all ofthe sensors have not been checked against the test bill, the system 10 loops to step 2310. Steps 2310-2395 are repeated until all the sensors are checked. Then, the system 10 proceeds to step 2400 where the system 10 determines whether the results for all three sensors are different, i.e., whether they each selected a different master pattern. If each sensor selected a different master pattern, the system 10 displays a "no call" message to the operator indicating that the bill can not be denominated. Otherwise, the system 10 proceeds to step 2410 where the system 10 determines whether the results for all three sensors are alike, i.e., whether they all selected the same master pattern. If each sensor selected the same master pattern, the system 10 proceeds to step 2415. Otherwise, the system 10 proceeds to step 2450 (FIG. 23d), to be discussed below. At step 2415, the system 10 determines whether the left sensor reading is above correlation threshold number one. If it is, the system 10 proceeds to step 2420. Otherwise, the system 10 proceeds to step 2430, to be discussed below. At step 2420, the system 10 determines whether the center sensor reading is above correlation threshold number one. If it is, the system 10 proceeds to step 2425. Otherwise, the 67 system 10 proceeds to step 2435, to be discussed below. At step 2425, the system 10 determines whether the right sensor reading is above correlation threshold number one. If it is, the system 10 proceeds to step 2475 where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2440, to be discussed below. At step 2430, the system 10 determines whether the center and right sensor readings are above correlation threshold number two. If they are, the system 10 proceeds to step 2475 (FIG. 23d) where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2445 (FIG. 23 d), to be discussed below. At step 2435, the system 10 determines whether the left and right sensor readings are above correlation threshold number two. If they are, the system 10 proceeds to step 2475 where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2445, to be discussed below. At step 2440, the system 10 determines whether the center and left sensor readings are above correlation threshold number two. If they are, the system 10 proceeds to step 2475 where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2445 where the system 10 determines whether all three color sums are below a threshold. If they are, the system 10 proceeds to step 2475 where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2480 where the system 10 displays a "no call" message to the operator indicating that the bill can not be denominated. At step 2410 the system 10 determined whether the results for all three ofthe sensors 2410 were alike, i.e., whether the master pattern denomination selected for each sensor is the same. If the results for all three sensors were not alike, the system 10 proceeded to step 2450 where the system 10 determines whether the left and center sensors are alike, i.e., whether they selected the same master pattern. If they did select the same master pattern, the system 10 proceeds to step 2460. Otherwise, the system 10 proceeds to step 2455, to be discussed below. At step 2455, the system 10 determines whether the center and right sensors are alike, i.e., whether they selected the same master pattern. If they did select the same master pattern, the system 10 proceeds to step 2465. Otherwise, the system 10 proceeds to step 2470, to be discussed below. At step 2465, the system 10 determines whether the center and right sensor readings are above threshold number three. If they are, the system 10 proceeds to step 2475 where the 68 denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2480 where the system 10 displays a "no call" message to the operator indicating that the bill can not be denominated. The system proceeded to step 2460 if the results ofthe left and center sensor readings were alike, i.e., selected the same master pattern. At step 2460, the system 10 determines whether the left and center sensor readings are above threshold number three. If they are, the system 10 proceeds to step 2475 where the denomination ofthe bill is called. Otherwise, the system 10 proceeds to step 2480 where the system 10 displays a "no call" message to the operator indicating that the bill can not be denominated. FIGS. 24a - 24h are flow charts illustrating a main routine and subroutines which may be substituted for the flow charts of FIGS. 23c-d. Points F and G of FIG. 24a connect to points F and G in FIGS. 23a-b. FIG. 25a shows a "main" routine. FIG. 24b shows a "THRCHK" subroutine. FIG. 24c and 24d show a "PATTCHK" subroutine, FIG. 24e shows a "FINSUMS" subroutine, and FIGS. 24f, 24g and 24h show a "COLRES" subroutine. An alternative comparison method comprises comparing the individual test hue samples to their corresponding master hue samples. If the test hue samples are within a range of 8% ofthe master hues, then a match is recorded. If the test and master hue comparison records a threshold number of matches, such as 62 out ofthe 64 samples, the brightness patterns are compared as described in the above method. While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope ofthe present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope ofthe claimed invention, which is set forth in the following claims.

Claims: 69 WHAT IS CLAIMED IS: 1. A document handling system for processing documents, the system comprising: a first sensor for scanning at least one characteristic of a document other than color, a full color sensor for scanning color characteristics ofthe document, and a processor for processing data corresponding to the characteristics scanned from one or more documents with the first sensor and the color sensor and for using the data to evaluate one or more documents. 2. The system of claim 1 wherein said full color sensor includes a plurality of color cells, each cell comprising a primary color sensor for sensing each of at least two primary colors and producing a corresponding output signal. 3. The system of claim 2 wherein said full color sensor is part of a color module, said color module further including an edge sensor located to one side of said color cells for detecting at least the presence of a document adjacent said color cells. 4. The system of claim 2 wherein each of said primary color sensors comprises an optical sensor and an optical filter. 5. The system of claim 2 wherein each of said primary color sensors generates analog signals representing variations in the respective primary color contents of a document being scanned, and further including an analog to digital converter for converting said analog signals to digital signals. 6. The system of claim 3 wherein said module further includes a light source, and wherein said primary color sensors are positioned for detecting light from said light source reflected from a bill being scanned and producing corresponding output signals. 7. The system of claim 4 said optical filters comprise dichroic color separation glass filters. 8. The system of claim 2 wherein each of said primary color sensors comprises a photodiode having a relatively large sensor area. 9. The system of claim 5 and further including a memory for storing the digital signals from two of said primary color sensors, and wherein said processor 70 determines a value ofthe third primary color content ofthe document from the two digital signals stored by the memory. 10. The system of claim 2 wherein each of said color cells is positioned for viewing a strip of a document being scanned and for producing continuous output signals corresponding to the color content of light reflected from said strip. 11. The system of claim 10 and further including an encoder operatively coupled with said color cells for defining sampling intervals for sampling said output signals in synchronization with movement of a document relative to said full color sensor. 12. The system of claim 11 wherein said encoder selects said sampling intervals such that successive samples of said output signals overlap one another. 13. The system of claim 6 and further including an encoder operatively coupled with said primary color sensors for defining sampling intervals for sampling output signals in synchronization with movement of a document relative to said color module. 14. The system of claim 13 wherein said encoder synchronizes the sampling intervals with an operating frequency ofthe light source. 15. The system of claim 2 wherein said processor is responsive to respective signals developed by said primary color sensors for developing a total brightness signal comprising the sum ofthe output signals from said primary color sensors and respective hue signals for each ofthe primary color sensors corresponding to the percentage ofthe total brightness signal that each ofthe output signals constitutes. 16. The system of claim 1 and further including a memory for storing master color characteristic data associated with each genuine document which the system is capable of discriminating, and wherein said processor compares the color characteristics scanned from a document with at least some ofthe master color characteristic data stored in said memory. 17. The system of claim 16 wherein said processor is operable in a learn mode for delivering data to said memory corresponding to characteristics scanned from a document by said full color sensor, when the scanned document is a genuine document, said data comprising master color characteristic data. 71 18. The system of claim 3 wherein one of said color modules is provided for scanning color characteristics on one side of a document . 19. The system of claim 18 wherein a second color module is provided for scanning color characteristics on the other side of a document. 20. The system of claim 16 wherein said master color characteristics include a plurality of sets of data, one for each of at least four possible orientations of a document, as a document moves relative to said sensor. 21. The system of claim 1 and further including a housing for mounting all components of said document handling system, said housing being relatively compact so as to fit on a table top, desk, work station, teller station and the like. 22. The system of claim 21 wherein said housing has a footprint of no more than about 11 inches by about 12 inches. 23. The system of claim 21 wherein said housing has a footprint of no more than about 15 inches by 20 inches. 24. The system of claim 21 wherein the housing and components of said document handling system weighs not more than from about 35 pounds to about 50 pounds. 25. The system of claim 16 wherein said memory contains master color characteristic data corresponding to color characteristics of documents comprising genuine bills of each of a plurality of denominations from the currency systems of each of a plurality of countries. 26. The system of claim 16 wherein said memory contains master color characteristic data corresponding to color characteristics of a plurality of denominations of documents including at least one type of casino script. 27. The system of claim 1 and further including a memory for storing master color characteristic data corresponding to color characteristics of genuine documents which the system is capable of discriminating and master pattern data corresponding to at least one other characteristic of each genuine document which the system is capable of discriminating and wherein said signal processing means compares said master color characteristic data with the color characteristic scanned from said document and selects 72 master pattern data corresponding to one or more potentially matching genuine documents for comparison with the characteristic scanned by said first sensor based at least in part on the color comparison. 28. The system of claim 1 wherein said first sensor comprises an optical sensor. 29. The system of claim 1 wherein said first sensor comprises a magnetic sensor. 30. The system of claim 1 wherein said first sensor comprises a UV sensor. 31. A document scanning system comprising a first scanhead assembly for scanning a first side of a document, said first scanhead assembly including at least one optical sensor for scanning optical characteristics of a document and size sensors comprising a pair of laterally spaced apart linear optical arrays extending a predetermined distance oppositely laterally outwardly for detecting opposite side edges of a document, for determining the length of a document in a direction transverse to a path of travel of a document past said scanhead. 32. The system of claim 31 wherein said optical sensor also senses a leading edge of a document and a trailing edge of a document, whereby the length of a document in the direction the path of travel can be determined. 33. The system of claim 31 and further including a leading and trailing edge detector for detecting leading and trailing edges of a document, whereby the length of a document in the direction ofthe path of travel can be determined. 34. The system of claim 31 and further including at least one additional optical sensor for developing a signal corresponding to the density of a document. 35. The system of claim 31 and further including a second scanhead assembly positioned for scanning a side of a document opposite the side scanned by said first scanhead assembly, said second scanhead assembly including a full color sensor for scanning color characteristics ofthe document. 36. The system of claim 35 wherein said second scanhead further includes a magnetic sensor for scanning magnetic characteristics ofthe document. 37. The system of claim 35 wherein said second scanhead further includes a UV sensor for scanning UV characteristics ofthe document. 73 38. A document scanning system comprising a first scanhead assembly for scanning a first side of a document, said first scanhead assembly including size sensors comprising a pair of laterally spaced apart linear optical arrays extending a predetermined distance oppositely laterally outwardly for detecting opposite side edges of a document, for determining the length of a document in a direction transverse to a path of travel of a document past said scanhead. 39. The system of claim 38 and further including at least one additional sensor for sensing a leading edge of a document and a trailing edge of a document, whereby the length of a document in the direction the path of travel can be determined. 40. A document handling method for processing documents, the method comprising the steps of: scanning at least one characteristic of a document other than color, scanning full color characteristics ofthe document, processing data corresponding to the color and other characteristics scanned from one or more documents, and using the data to evaluate one or more documents. 41. The method of claim 40 wherein the step of full color scanning includes sensing each of at least two primary colors and producing corresponding output signals. 42. The method of claim 41 and further including detecting at least the presence of a document. 43. The method of claim 41 wherein sensing said primary colors comprises optically filtering light reflected from a document and optically sensing the filtered light. 44. The method of claim 41 wherein said sensing of primary colors includes generating analog signals representing variations in at least two primary color contents of a document being scanned, and converting said analog signals to digital signals. 45. The method of claim 44 and further including the step of storing the digital signals corresponding to two of said primary colors and determining a value ofthe third primary color content ofthe document from the two stored digital signals. 74 46. The method of claim 41 wherein the step of full color scanning includes viewing a strip of a document and producing continuous output signals corresponding to the color content of light reflected from said strip. 47. The method of claim 46 wherein the step of processing includes defining sampling intervals for sampling said output signals in synchronization with movement of a document relative to said full color sensor. 48. The method of claim 47 wherein said sampling intervals are selected such that successive samples of said output signals overlap one another. 49. The method of claim 47 and further including synchronizing the sampling intervals with an operating frequency of a light source. 50. The method of claim 41 wherein the step of processing includes developing a total brightness signal comprising the sum ofthe output signals and respective hue signals for each ofthe primary colors corresponding to the percentage of the total brightness signal that each ofthe output signals constitutes. 51. The method of claim 40 and further including the steps of storing master color characteristic data associated with each genuine document which the system is capable of discriminating, and comparing the color characteristics scanned from a document with at least some ofthe stored master color characteristic data. 52. The method of claim 41 and further including operating in a learn mode for storing data corresponding to the color characteristics scanned from a document when the scanned document is a genuine document, said data comprising master color characteristic data. 53. The method of claim 40 wherein the step of scanning full color characteristics includes scanning full color characteristics on both sides of a document. 54. The method of claim 51 wherein said master color characteristics include a plurality of sets of data, one for each of at least four possible orientations of a document. 55. The method of claim 40 and further including the step of storing master color characteristic data corresponding to color characteristics of genuine documents which the method is capable of discriminating and master pattern data corresponding to at least one other characteristic of each genuine document which the system is capable of 75 discriminating and wherein the step of processing comprises comparing said master color characteristic data with the color characteristic scanned from said document and selecting master pattern data corresponding to one or more potentially matching genuine documents for comparison with said scanned other characteristic based at least in part on the color comparison. 56. A color scanhead apparatus for a document handling system, said color scanhead comprising a full color sensor including a plurality of color cells, each cell comprising a primary color sensor for sensing each of at least two primary colors. 57. The apparatus of claim 56 and further including an edge sensor located to one side of said color cells for detecting at least the presence of a document adjacent said color cells. 58. The apparatus of claim 56 wherein each of said primary color sensors comprises an optical sensor and an optical filter. 59. The apparatus of claim 56 and further including a light source, and wherein said primary color sensors are positioned for detecting light from said light source reflected from a bill being scanned. 60. The apparatus of claim 58 said optical filters comprise dichroic color separation glass filters. 61. The apparatus of claim 56 wherein each of said primary color sensors comprises a photodiode having a relatively large sensor area. 62. The apparatus of claim 56 wherein said scanhead includes at least one light source positioned relatively close to a transport path along which a document moves adjacent to said scanhead. 63. The apparatus of claim 62 wherein said light source comprises at least one fluorescent tube providing white light with a high intensity in red, blue and green wavelengths. 64. The apparatus of claim 62 wherein said scanhead further includes a glass shield positioned between the light source and the transport path. 65. The apparatus of claim 62 and further including a mask interposed between said light source and said primary color sensors, said mask having a reflective 76 surface facing the light source and a relatively narrow slit for transmitting reflected light to the primary color sensors. 66. The apparatus of claim 65 and further including a manifold positioned between said mask and said primary color sensors for substantially limiting light reaching the sensors to light reflected through said slit in said mask. 67. The apparatus of claim 66 wherein said manifold has interior surfaces formed at an angle such that the width ofthe manifold adjacent the mask is greater than the width ofthe manifold adjacent said primary color sensors for substantially trapping light reflected through said slit. 68. The apparatus of claim 67 wherein the interior surfaces of said manifold are coated with a light absorbing material to substantially prevent noisy light from reaching to the primary color sensors. 69. The apparatus of claim 58 wherein said color scanheads includes a scanhead body having a plurality of sensor receptacles, said optical sensors and said optical filters being positioned in said receptacles, each receptacle having one optical sensor positioned behind a corresponding optical filter. 70. The apparatus of claim 69 wherein adjacent ones of said receptacles form a color cell, for respectively receiving one each of said primary color sensors, said scanhead body further including cell partitions extending between adjacent color cells. 71. The apparatus of claim 70 and further including a mask interposed between said light source and said primary color sensors, said mask having a reflective surface facing the light source and a relatively narrow slit for transmitting reflected light to the primary color sensors. 72. The apparatus of claim 71 and further including a manifold position between said mask and said primary color sensors for substantially limiting light reaching the sensors to light reflected through said slit in said mask, said cell partitions running substantially from a sensor end to a mask end of each cell. 73. The apparatus of claim 70 wherein at least one of said cells mounts a document edge sensor in place of a primary color sensor. 74. A color scanning method for a document handling system for processing documents, the method comprising the steps of: 77 scanning full color characteristics of a document, processing data corresponding to the characteristics scanned from one or more documents, and using the data to evaluate one or more documents. 75. The method of claim 74 wherein the step of full color scanning includes sensing each of at least two primary colors and producing corresponding output signals. 76. The method of claim 74 and further including detecting at least the presence of a document. 77. The method of claim 75 wherein sensing said primary colors comprises optically filtering light reflected from a document and optically sensing the filtered light. 78. The method of claim 75 wherein said sensing of primary colors includes generating analog signals representing variations in at least two primary color contents of a document being scanned, and converting said analog signals to digital signals. 79. The method of claim 78 and further including the step of storing the digital signals corresponding to two of said primary colors and determining a value ofthe third primary color content ofthe document from the two stored digital signals. 80. The method of claim 75 wherein the step of full color scanning includes viewing a strip of a document and producing continuous output signals corresponding to the color content of light reflected from said strip. 81. The method of claim 80 wherein the step of processing includes defining sampling intervals for sampling said output signals in synchronization with movement of a document relative to said full color sensor. 82. The method of claim 81 wherein said sampling intervals are selected such that successive samples of said output signals overlap one another. 83. The method of claim 81 and further including synchronizing the sampling intervals with an operating frequency of a light source. 84. The method of claim 75 wherein the step of processing includes developing a total brightness signal comprising the sum ofthe output signals and respective hue signals for each ofthe primary colors corresponding to a percentage ofthe total brightness signal that each ofthe output signals constitutes. 78 85. The method of claim 74 and further including the steps of storing master color characteristic data associated with each genuine document which the system is capable of discriminating, and comparing the color characteristics scanned from a document with at least some ofthe stored master color characteristic data. 86. The method of claim 76 wherein the step of scanning full color characteristics includes scanning full color characteristics on both sides of a document. 87. The method of claim 85 wherein said master color characteristics include a plurality of sets of data, one for each of at least four possible orientations of a document.

Inventors: ANDERSON MATTHEW L, CSULITS FRANK M, GRAVES BRADFORD T, JENRICK CHARLES P, MAZUR RICHARD A, MENNIE DOUGLAS U, WATTS GARY P, ANDERSON, MATTHEW, L., CSULITS, FRANK, M., GRAVES, BRADFORD, T., JENRICK, CHARLES, P., MAZUR, RICHARD, A., MENNIE, DOUGLAS, U., WATTS, GARY, P.
Applicants: CUMMINS ALLISON CORP, CUMMINS-ALLISON CORP.
Application year: 1999
Main classification: G06K9
IPC codes: G07D3, G07D7, G07D11, H04N1