Abstract:
There is described in one embodiment an imaging apparatus having an image sensor, and a plurality of operating states. Operation of the imaging apparatus can be differentiated between the operating states. In one operating state, the imaging apparatus can capture a frame of image data having image data corresponding to a predetermined number of pixels of the image sensor. The operating states of the imaging apparatus can be user selectable. There is described in one embodiment an apparatus having an image sensor operative to capture a relatively smaller sized frame, wherein a characteristic of light directed by an illumination assembly for capture of a relatively larger sized frame is determined utilizing the relatively smaller sized frame.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 12/371,277, filed Feb. 13, 2009, entitled “Imaging Apparatus Having Plurality of Operating States,” which is incorporated herein by reference in its entirety and which is a divisional application of U.S. patent application Ser. No. 11/895,803, filed Aug. 27, 2007, (U.S. Patent Application Publication No. 2008/0170275, entitled, “Bar Code Reading Device Having Plurality of Operating States” which is incorporated herein by reference in its entirety, which a divisional application of U.S. patent application Ser. No. 09/766,922, filed Jan. 22, 2001, (U.S. Pat. No. 7,268,924) entitled, “Optical Reader Having Reduced Parameter Determination Delay” which is incorporated herein by reference in its entirety. In addition, the present application incorporates by reference in its entirety U.S. patent application Ser. No. 09/766,806 (now U.S. Pat. No. 6,637,658 B2) filed Jan. 22, 2001 entitled, “Optical Reader Having Partial Frame Operating Mode,” which application is incorporated by reference in the aforementioned U.S. patent application Ser. No. 09/766,922 filed Jan. 22, 2001. This application is also related to U.S. patent application Ser. No. 11/238,176, filed Sep. 28, 2005, (U.S. Pat. No. 7,428,079) entitled “Bar code reading device having partial frame image capture operating mode,” U.S. patent application Ser. No. 10/651,298, filed Aug. 28, 2003, (U.S. Pat. No. 7,270,273) entitled “Optical Reader Having Partial Frame Operating Mode,” and U.S. patent application Ser. No. 11/637,231, filed Dec. 11, 2006 (U.S. Pat. No. 7,434,733) entitled “Optical Reader Having Partial Frame Operating Mode,” and U.S. patent application Ser. No. 12/249,742, filed Oct. 10, 2008 entitled “Reading Apparatus Having Partial Frame Operating Mode.” 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a bar code reading device generally and particularly to a bar code reading device having a plurality of operating states. 
     BACKGROUND OF THE PRIOR ART 
     Prior to commencing comprehensive image data processing, which may include e.g., searching for symbol or character representations, decoding and character recognition processing, presently available optical readers clock out and capture in a memory location at least one exposure test frame of image data, read pixel data from the memory-stored exposure test frame to determine an exposure parameter value that is based on actual illumination conditions, then utilize the exposure parameter value in the exposure of a frame of image data that is clocked out, and then subjected to searching, decoding, and/or character recognition processing. The frame of image data exposed utilizing the exposure parameter based on actual illumination conditions is not available for reading until after it is clocked out. Presently available optical readers therefore exhibit an appreciable inherent exposure parameter determination delay. Readers having higher resolution imagers have slower frame clock out rates and therefore longer exposure parameter determination delays. 
     There is a growing demand for higher resolution optical readers, including optical readers that incorporate mega pixel image sensors. Accordingly, there is growing need to address the parameter determination delay problem associated with presently available optical readers. 
     Optical readers having 2D image sensors commonly are used to read both 1D and 2D symbols. Some optical readers having a 2D image sensor read a 1D symbol by capturing a 2D image representation, or “frame” of image data corresponding to a target area which comprises a 1D symbol, and launching a scan line or lines in order to attempt to decode for 1D symbols which may be represented in the area. Other optical readers having 2D image sensors read 1D symbols by capturing a 2D image representation of an area containing the 1D symbol, preliminarily analyzing the image data represented in the area to determine that the image data comprises a representation of a 1D symbol, and then launching a scan line in an attempt to decode for the 1D symbol determined to be present. In either case, a full frame 2D image representation is captured in order to decode for a 1D symbol. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIGS. 1   a  and  1   b  are image maps illustrating possible low resolution frames of image data clock out during a low resolution frame clock out mode of the invention; 
         FIG. 2   a  is a block diagram of an optical reader of a type in which the invention may be incorporated; 
         FIGS. 2   b - 2   h  show various types of optical reader housings in which the invention may be incorporated; 
         FIG. 3   a  is a process flow diagram illustrating frame clocking operations in an optical reader having an image sensor including a one-frame buffer; 
         FIG. 3   b  is a time line illustrating frame clock out operations in a prior art optical reader; 
         FIG. 3   c  is a time line illustrating a frame clock out of operations in an optical reader operated according to the invention. 
       [Beginning of section excerpted from U.S. patent application Ser. No. 09/766,806]. 
         FIGS. 4   a - 4   g  illustrate various image data patterns that may be captured by an optical reader operating in a partial frame capture mode according to the invention; 
         FIG. 5   a  is a block diagram of an optical reader of a type in which the invention may be incorporated; 
         FIGS. 5   b - 5   h  show various types of optical reader housings in which the invention may be incorporated. 
       [End of section excerpted from U.S. patent application Ser. No. 09/766,806]. 
     
    
    
     SUMMARY OF THE INVENTION 
     There is described in one embodiment an imaging apparatus having an image sensor, and a plurality of operating states. Operation of the imaging apparatus can be differentiated between the operating states. In one operating state, the imaging apparatus can capture a frame of image data having image data corresponding to a predetermined number of pixels of the image sensor. The operating states of the imaging apparatus can be user selectable. There is described in one embodiment an apparatus having an image sensor operative to capture a relatively smaller sized frame, wherein a characteristic of light directed by an illumination assembly for capture of a relatively larger sized frame is determined utilizing the relatively smaller sized frame. 
     DETAILED DESCRIPTION OF THE INVENTION 
     When operated to generate valid pixel data, presently available optical reading devices clock out electrical signals corresponding to pixel positions of an image sensor at a uniform clock out rate such that the electrical signal corresponding to each pixel of the image sensor array accurately represents light incident on the pixel. 
     By contrast, an image sensor of the present invention is made to operate under two major frame capture modes, a “low resolution” frame clock out mode and a “normal resolution” frame clock out mode. In a “low resolution” mode of operation, an image sensor according to the invention is operated to clock out electrical signals corresponding to some pixels of an image sensor array at a high clock out rate and other pixels of the image sensor at a normal clock out rate. Clocking out a portion of the electrical signals using a faster than normal clock out rate results in a reduction in the overall frame clock out time while clocking out a portion of the signals at a normal clock out rate enables the generation of pixel data sufficient to enable determination of parameter settings for use in subsequent frame captures. In a “normal resolution” mode of operation the image sensor is operated to clock out electrical signals corresponding to pixels of the array using a single uniform clock out speed as in prior art readers. The low resolution mode of operation may also be carried out by clocking out electrical signals corresponding to only a portion of a frame&#39;s pixels and not clocking out electrical signals corresponding to the remaining pixels. 
     A reader configured in accordance with the invention clocks out and captures in a memory storage location at least one parameter determination frame of image data in a “low resolution” frame capture mode, reads pixels of the parameter determination frame in establishing at least one operation parameter that is based on actual illumination conditions, utilizes the determined operation parameter in clocking out a subsequent frame of image data in a “normal resolution mode,” then captures and subjects the frame of image data clocked out utilizing the operation parameter to image data searching, decoding, and/or recognition processing. The reader may be adapted to decode a decodable symbol represented in a frame of image data developed utilizing a determined operating parameter. 
     An optical reading system is which the invention may be employed is described with reference to the block diagram of  FIG. 2   a.    
     Optical reader  10  includes an illumination assembly  20  for illuminating a target object T, such as a 1D or 2D bar code symbol, and an imaging assembly  30  for receiving an image of object T and generating an electrical output signal indicative of the data optically encoded therein. Illumination assembly  20  may, for example, include an illumination source assembly  22 , together with an illuminating optics assembly  24 , such as one or more lenses, diffusers, wedges, reflectors or a combination of such elements, for directing light from light source  22  in the direction of a target object T. Illumination assembly  20  may comprise, for example, laser or light emitting diodes (LEDs) such as white LEDs or red LEDs. Illumination assembly  20  may include target illumination and optics for projecting an aiming pattern  27  on target T. Illumination assembly  20  may be eliminated if ambient light levels are certain to be high enough to allow high quality images of object T to be taken. Imaging assembly  30  may include an image sensor  32 , such as a 1D or 2D CCD, CMOS, NMOS, PMOS, CID OR CMD solid state image sensor, together with an imaging optics assembly  34  for receiving and focusing an image of object T onto image sensor  32 . The array-based imaging assembly shown in  FIG. 2   a  may be replaced by a laser array based imaging assembly comprising multiple laser sources, a scanning mechanism, emit and receive optics, at least one photodetector and accompanying signal processing circuitry. 
     Optical reader  10  of  FIG. 2   a  also includes programmable control circuit  40  which preferably comprises an integrated circuit microprocessor  42  and an application specific integrated circuit (ASIC  44 ). The function of ASIC  44  could also be provided by field programmable gate array (FPGA). Processor  42  and ASIC  44  are both programmable control devices which are able to receive, output and process data in accordance with a stored program stored in memory unit  45  which may comprise such memory elements as a read/write random access memory or RAM  46  and an erasable read only memory or EROM  47 . RAM  46  typically includes at least one volatile memory device but may include one or more long term non-volatile memory devices. Processor  42  and ASIC  44  are also both connected to a common bus  48  through which program data and working data, including address data, may be received and transmitted in either direction to any circuitry that is also connected thereto. Processor  42  and ASIC  44  differ from one another, however, in how they are made and how they are used. 
     More particularly, processor  42  is preferably a general purpose, off-the-shelf VLSI integrated circuit microprocessor which has overall control of the circuitry of  FIG. 2   a , but which devotes most of its time to decoding image data stored in RAM  46  in accordance with program data stored in EROM  47 . Processor  44 , on the other hand, is preferably a special purpose VLSI integrated circuit, such as a programmable logic or gate array, which is programmed to devote its time to functions other than decoding image data, and thereby relieve processor  42  from the burden of performing these functions. 
     The actual division of labor between processors  42  and  44  will naturally depend on the type of off-the-shelf microprocessors that are available, the type of image sensor which is used, the rate at which image data is output by imaging assembly  30 , etc. There is nothing in principle, however, that requires that any particular division of labor be made between processors  42  and  44 , or even that such a division be made at all. This is because special purpose processor  44  may be eliminated entirely if general purpose processor  42  is fast enough and powerful enough to perform all of the functions contemplated by the present invention. It will, therefore, be understood that neither the number of processors used, nor the division of labor there between, is of any fundamental significance for purposes of the present invention. 
     With processor architectures of the type shown in  FIG. 2   a , a typical division of labor between processors  42  and  44  will be as follows. Processor  42  is preferably devoted primarily to such tasks as decoding image data, once such data has been stored in RAM  46 , recognizing characters represented in stored image data according to an optical character recognition (OCR) scheme, handling menuing options and reprogramming functions, processing commands and data received from control/data input unit  39  which may comprise such elements as trigger  74  and keyboard  78  and providing overall system level coordination. 
     Processor  44  is preferably devoted primarily to controlling the image acquisition process, the A/D conversion process and the storage of image data, including the ability to access memories  46  and  47  via a DMA channel. Processor  44  may also perform many timing and communication operations. Processor  44  may, for example, control the illumination of LEDs  22 , the timing of image sensor  32  and an analog-to-digital (A/D) converter  36 , the transmission and reception of data to and from a processor external to reader  10 , through an RS-232, a network such as an Ethernet, a serial bus such as USB, a wireless communication link (or other) compatible I/O interface  37 . Processor  44  may also control the outputting of user perceptible data via an output device  38 , such as a beeper, a good read LED and/or a display monitor which may be provided by a liquid crystal display such as display  82 . Control of output, display and I/O functions may also be shared between processors  42  and  44 , as suggested by bus driver I/O and output/display devices  37 ′ and  38 ′ or may be duplicated, as suggested by microprocessor serial I/O ports  42 A and  42 B and I/O and display devices  37 ″ and  38 ′. As explained earlier, the specifics of this division of labor is of no significance to the present invention. 
       FIGS. 2   b  through  2   g  show examples of types of housings in which the present invention may be incorporated.  FIGS. 2   b - 2   g  show 1D/2D optical readers  10 - 1 ,  10 - 2  and  10 - 3 . Housing  12  of each of the optical readers  10 - 1  through  10 - 3  is adapted to be graspable by a human hand and has incorporated therein at least one trigger switch  74  for activating image capture and decoding and/or image capture and character recognition operations. Readers  10 - 1  and  10 - 2  include hard-wired communication links  79  for communication with external devices such as other data collection devices or a host processor, while reader  10 - 3  includes an antenna  80  for providing wireless communication device or a host processor. 
     In addition to the above elements, readers  10 - 2  and  10 - 3  each include a display  82  for displaying information to a user and a keyboard  78  for enabling a user to input commands and data into the reader. 
     Any one of the readers described with reference to  FIGS. 2   b  through  2   g  may be mounted in a stationary position as is illustrated in  FIG. 2   h  showing a generic optical reader  10  docked in a scan stand  90 . Scan stand  90  adapts portable optical reader  10  for presentation mode scanning. In a presentation mode, reader  10  is held in a stationary position and an indicia bearing article is moved across the field of view of reader  10 . 
     As will become clear from the ensuing description, the invention need not be incorporated in a portable optical reader. The invention may also be incorporated, for example, in association with a control circuit for controlling a non-portable fixed mount imaging assembly that captures image data representing image information formed on articles transported by an assembly line, or manually transported across a checkout counter at a retail point of sale location. Further, in portable embodiments of the invention, the reader need not be hand held. The reader may be part or wholly hand worn, finger worn, waist worn or head worn for example. 
     Referring again to particular aspects of the invention, a low resolution frame clock out mode of the invention is described in detail with reference to the pixel maps of  FIGS. 1   a  and  1   b . Control circuit  40  establishes a clock out rate for clocking out an electrical signal corresponding to a pixel of an image sensor  32  by appropriate state control of control signals in communication with image sensor  32 . In the present invention, image sensor  32  is selected to be of a type whose pixel clock out rate can be varied by way of control signals received from control circuit  40 . In presently available optical readers, an image sensor&#39;s pixel clock out rate is not changed during the course of clocking out of a frame of image data. 
     In a “low resolution” frame clock out mode of the invention, however, control circuit  40  causes image sensor  32  to clock out electrical signals corresponding to the pixels of the array at least two speeds during a single frame capture period. During a single frame clock out period, control circuit  40  controls image sensor  32  so that some pixels are clocked out at normal clock out rate sufficient to develop electrical signals accurately representing the intensity of light at the respective pixel positions, while other pixels are either not clocked out or are clocked out at a clock out rate which may be insufficient to allow development of electrical signals that accurately represent the intensity of light at the respective pixels but which nevertheless results in a reduction of the overall frame clock out time of the frame of image data being clocked out. 
       FIG. 1   a  shows a schematic diagram of an exemplary image map frame that is clocked out according to the low resolution frame clock out mode of the invention and then captured into memory  45 . The image map is divided into “zones” of valid data and invalid data. Valid zones  84  shown are rows of pixels that are clocked out at a normal clock out speed while invalid zones  86  shown are rows of pixels that are clocked out at a faster clock out speed, which is normally (but not necessarily) a speed insufficient to allow development of electrical signals accurately representing the intensity of light at a pixel. 
       FIG. 1   b  shows another possible division of an image map into valid zones and invalid zones. This type of embodiment in which valid zones  84  comprise less than full pixel rows is conveniently realized by appropriate control of an image sensor manufactured using CMOS fabrication methods. Using CMOS fabrication methods, an image sensor can be merged with a microprocessor, an ASIC, or another timing device on a single die to the end that a pre-established clocking sequence in which a pixel clock out rate is changed multiple times during the course of clock out a frame of image data may be actuated in response to the activation of a single control signal in communication with image sensor  32 . 
     Using CMOS fabrication techniques, image sensors are readily made so that electrical signals corresponding to certain pixels of a sensor can be selectively clocked out without clocking out electrical signals corresponding to remaining pixels of the sensor. CMOS image sensors are available from such manufacturers as Symagery, Pixel Cam, Omni Vision, Sharp, Natural Semiconductor, Toshiba, Hewlett-Packard and Mitsubishi. Further aspects of a partial frame clock out mode are described in commonly assigned U.S. application Ser. No. 09/766,806 entitled “Optical Reader Having Partial Frame Operating Mode,” now U.S. Pat. No. 6,637,658 filed concurrently herewith and incorporated herein by reference. 
     The invention is also conveniently realized with use of an image sensor having an image sensor discharge function. Image sensors having a discharge function are typically adapted to receive a discharge clock out signal which when active results in all pixels of a frame being read out at a high clock out rate insufficient to allow development of electrical signals. In presently available readers having a directional function, a control circuit sets the discharge clocking signal to an active state while clocking out an initial “discharge period” frame of image data immediately after reception of a trigger actuation. This initial discharge process removes any residual charges built up on image sensor  32  prior to capturing a first frame including valid pixel data. 
     For producing an image map divided into valid and invalid zones using an image sensor having a discharge function, control circuit  40  may be made to intermittently change the state of a discharge clock out signal during a frame clock out period during which image sensor  32  is otherwise operated according to a normal resolution clock out mode. 
     An exemplary embodiment of the invention in which the invention is employed in a reader equipped with a SONY ICX084AL CCD image sensor (that includes a one frame analog buffer memory) and a SONY CXD2434TQ timing generator is described with reference to  FIGS. 3   a ,  3   b  and  3   c .  FIG. 3   a  shows a flow diagram, of an imaging system in which the image sensor includes a one frame buffer memory. For purposes of illustrating the advantages of the invention,  FIG. 3   b  shows a time line illustrating the time required to clock out and capture a frame of image data useful for searching and decoding in a prior art reader having a buffer memory not configured to operate in accordance with a low resolution frame clock out mode.  FIG. 3   c  shows a time line illustrating the time required to clock out and capture a frame of image data useful for searching, decoding, and recognizing characters in a reader having a buffer memory configured to operate in a low resolution frame clock out mode according to the invention. 
     When a reader includes a one frame buffer memory, then the activation of an appropriate frame clock out signal by image sensor  32  causes electrical charges representative of light on pixels of an image sensor&#39;s pixel array  32   a  to be transferred to analog buffer memory  32   b  and causes electrical signals corresponding to pixel value storage locations of buffer  32   b  (representing light on the pixels during a previous timing period) to be clocked out to analog to digital converter  36  so that the frame of image data stored on buffer memory can be captured in memory  45 , wherein the data may be read by control circuit  40 . 
     Referring to time line  92  corresponding a prior art reader it can be seen that a substantial parameter determination delay is present without use of a low resolution frame capture mode according to the invention. At time T0, control circuit  40  activates a frame discharge control signal so that residual charges built up in the storage locations of buffer memory  32   b  are eliminated or “cleaned” during clock out period CPO. 
     At time T 1 , control circuit  40  activates a frame clocking signal to commence the clock out a first frame of pixel data according to a normal resolution frame clock out mode (the pixel data clocked out during clock out period CP 1  is normally invalid pixel data). During clock out period CP 1 , the charges built up on pixel array  32   a  during clock out period CP 0  are transferred to buffer memory  32   b  and then clocked out to A/D converter  36 . Also during clock out period CP 1  pixel array  32   a  is exposed to light for a time determined by an exposure parameter value, e 0 , that was previously transmitted at time Te 0  prior to time T 1 . The exposure parameter e 0  is based on previous exposure values during a previous trigger actuation period or based on expected illumination conditions, but is not based on actual illumination conditions present. 
     At time T 2 , control circuit  40  activates a frame clock out signal to commence the clock out of a second frame of image data in accordance with a normal resolution frame clock out mode. During clock out period CP 2 , the charges built up on pixel array  32   a  during clock out period CP 1  are transferred to buffer memory  32   b  and then clocked out to A/D converter  36 . Also during clock out period CP 2  pixel array  32  is exposed to light for a time determined by an exposure parameter value, e 1 , that was previously transmitted at time Te 1  prior to time T 2 . The exposure parameter e 1 , like exposure parameter e 0 , also cannot be based on actual illumination conditions since the most recent frame image data available for reading by circuit  40  prior to the transmittal of exposure parameter e 1  is the invalid frame data resulting from transmittal of frame discharge signal at time T 0 . 
     At time T 3 , control circuit  40  activates a frame clock out signal to commence the capture of a third frame of image data in accordance with a normal resolution frame clock out mode. During clock out period CP 3 , the charges built up on pixel array  32   a  during clock out period CP 2  are transferred to buffer memory  32   b  and then clocked out to A/D converter  36 . Also during clock out period CP 3 , pixel array  32   a  is exposed to light for a time determined by an exposure parameter value, e 2 , that was previously transmitted at time Te 2  prior to time T 3 . Unlike the previous exposure values e 0  and e 1 , the exposure parameter value e 2  can be a value determined from actual illumination conditions since the frame of image data resulting from pixel array  32   a  being exposed to light during clock out period CP 1 , is available for reading by control circuit  40  prior to the time that the exposure parameter e 2  must be communicated to image sensor  32 . However, because of the built in one frame delay resulting from the presence of buffer  32   b , it is seen that a frame of image data clocked out while being exposed with the exposure parameter value e 2 , determined based on actual illumination conditions, will not be available for reading by control circuit unit after the expiration of clocking period CP 4 . Accordingly, it can be seen that the above reader exhibits a typical parameter determination delay of four normal resolution clock out periods, CP 1 +CP 2 +CP 3 +CP 4  plus the frame discharge clock out parameter CP 0 . The normal resolution frame clock out period of the above-referenced SONY image sensor is about 33.37 ms and the frame discharge period is about 8.33 ms, resulting in a typical-case total parameter determination delay in the example described of 140 ms (an earlier frame may be subjected to image data searching, decoding, and recognition if e 0  or e 1  yields an image of acceptable quality). 
     Advantages of operating image sensor  32  according to a low resolution frame clock out mode of operation are easily observable with reference to time line  94  corresponding to a reader having an image sensor operated in accordance with a low resolution frame clock out mode. In the example illustrated by time line  94  control circuit  40  operates image sensor as described in connection with  FIG. 3   b  except that control circuit  40  operates image sensor  32  according to a low resolution frame clock out mode during clocking periods CP 1 , CP 2 , and CP 3 . Because electrical signals corresponding to only some of the pixels during these timing periods are clocked out at speeds sufficiently slow to read valid image data, the total frame clock out time associated with these clocking periods is significantly shorter than that of a frame clocked out according to a normal resolution frame clock out mode. In an exemplary embodiment in which control circuit  40  alternatingly changes the state of a discharge clock out control signal (known as an EFS signal) in communication with a SONY ICX084AL CCD image sensor, to result in a zone division pattern having valid zones comprising four pixel rows clocked out at normal speed bounded by invalid rows having eighteen rows of pixels clocked out at high speed, the low resolution frame clock out rate is 8.52 ms. The overall typical parameter determination delay is therefore reduced to T 0 +T 1 +T 2 +T 3 +T 4 =66.2 ms as compared to the 140 ms delay in the prior art reader example described with reference to  FIG. 3   a.    
     In the example described in which image sensor  32  comprises a one frame buffer  32   b , pixel array  32   a  is exposed to light for at least some time currently as electrical signals are clocked out from buffer  32   b . In the control of presently available image sensors that do not have one frame buffers, frame clock out periods normally follow frame exposure periods without overlapping the exposure periods. 
     A low resolution parameter determination frame of image data clocked out using a low resolution clock out mode is useful for determining an exposure control parameter because exposure parameter values can be accurately determined by sampling only a small percentage of pixel values from a frame of image data. In fact, for improving the processing speed of an optical reader it is preferred to determine an exposure control value based on a sampling of a small percentage of pixel values from a frame of image data. The proper exposure parameter setting varies substantially linearly with illumination conditions, and therefore is readily determined based on a sampling of pixel values from a single frame of image data. 
     Additional reader operating parameters can be determined by reading pixel values from a frame of image data clocked out according to a low resolution clock out mode of the invention. These additional parameters which may be determined from a low resolution parameter determining frame of image data include an amplification parameter for adjusting the gain of an amplifier prior to analog-to-digital conversion, an illumination level parameter for adjusting the current level delivered to, and therefore the radiance of light emitted from LEDs  22 , an illumination time parameter for adjusting the on-time of LEDs  22 , a light level parameter for adjusting a light level of a subsequently captured frame of image data, a dark level parameter for adjusting a dark level of a subsequently captured frame of image data, and an analog-to-digital converter reference parameter for adjusting a reference voltage of analog-to-digital converter  36 . 
     Referring to  FIGS. 4   a - 4   g  the invention is an optical reader equipped with a 2D image sensor that is configured to operate in a partial frame capture mode. In a partial frame clock out mode, a control circuit of an optical reader clocks out (or “reads”) electrical signals corresponding to less than all of the 2D image sensor&#39;s pixels, and captures image data corresponding to the pixel locations into memory. 
     Partial frames of image data which may be clocked out and captured by an optical reader control circuit during a partial frame capture mode are illustrated in  FIGS. 4   a - 4   g  in which valid zones  212  represent frame image data corresponding to image sensor pixel positions that are clocked out and invalid zones (indicated by the shaded regions of the views of  FIGS. 4   a - 4   g ) represent potential image data positions corresponding to pixel positions that are not clocked out. 
     Border  210  defines the full field of view of an optical reader in the case the reader is operated in a full frame captured mode while symbols  216 - 1 ,  216 - 2 ,  216 - 3 ,  216 - 4 ,  216 - 6  and  216 - 7  are symbols entirely within the full field of view of an optical reader defined by border  10  but are only partially within certain valid zones shown. Valid zones  212 - 1 ,  212 - 3 ,  212 - 7 ,  212 - 8 ,  212 - 9 ,  212 - 10 , and  212 - 13  are valid zones of image data that partially contain representations of a decodable symbol while valid zones  212 - 11  and  212 - 12  are valid zones of image data captured during a partial frame capture mode which contain representations of an entire decodable symbol. 
     In the examples illustrated with reference to  FIGS. 4   a - 4   e  an optical reader operating in a partial frame clock out mode clocks out electrical signals corresponding to linear patterns of pixels. It is useful to cause a reader to clock out electrical signals corresponding to linear patterns as shown in  FIGS. 4   a - 4   d  when a reader will be used to decode mainly 1D linear bar code symbols. 
     In the examples illustrated with reference to  FIGS. 4   f  and  4   g  an optical reader operating in a partial frame clock out mode clocks out electrical signals corresponding to non-linear groupings of pixels. It is useful to cause a reader to clock out electrical signals corresponding to pixel groupings as shown in  FIGS. 4   f  and  4   g  when a reader will be used to decode symbols which are expected to be within a certain position in an image sensor&#39;s field of view. 
     A reader may be configured so that the reader automatically switches out of partial frame capture mode on the sensing of a certain condition. For example a reader according to the invention may be made to switch out of partial frame capture operating mode and into a full frame capture mode on the sensing that a 2D symbol is partially represented in the partial frame of image data, or on the condition that processing of the partial frame of image data fails to result in image data being decoded. 
     An optical reading system in which the invention may be employed is described with reference to the block diagram of  FIG. 5   a.    
     Optical reader  110  includes an illumination assembly  120  for illuminating a target object T, such as a 1D or 2D bar code symbol, and an imaging assembly  130  for receiving an image of object T and generating an electrical output signal indicative of the data optically encoded therein. Illumination assembly  120  may, for example, include an illumination source assembly  122 , together with an illuminating optics assembly  124 , such as one or more lenses, diffusers, wedges, reflectors or a combination of such elements, for directing light from light source  122  in the direction of a target object T. Illumination assembly  120  may comprise, for example, laser or light emitting diodes (LEDs) such as white LEDs or red LEDs. Illumination assembly  120  may include target illumination and optics for projecting an aiming pattern  127  on target T. Illumination assembly  120  may be eliminated if ambient light levels are certain to be high enough to allow high quality images of object T to be taken. Imaging assembly  130  may include an image sensor  132 , such as a 1D or 2D CCD, CMOS, NMOS, PMOS, CID OR CMD solid state image sensor, together with an imaging optics assembly  134  for receiving and focusing an image of object T onto image sensor  132 . The array-based imaging assembly shown in  FIG. 5   a  may be replaced by a laser array based imaging assembly comprising multiple laser sources, a scanning mechanism, emit and receive optics, at least one photodetector and accompanying signal processing circuitry. 
     The partial frame clock out mode is readily implemented utilizing an image sensor which can be commanded to clock out partial frames of image data or which is configured with pixels that can be individually addressed. Using CMOS fabrication techniques, image sensors are readily made so that electrical signals corresponding to certain pixels of a sensor can be selectively clocked out without clocking out electrical signals corresponding to remaining pixels of the sensor. CMOS image sensors are available from such manufacturers as Symagery, Pixel Cam, Omni Vision, Sharp, National Semiconductor, Toshiba, Hewlett-Packard and Mitsubishi. A partial frame clock out mode can also be carried out by selectively activating a frame discharge signal during the course of clocking out a frame of image data from a CCD image sensor, as is explained in concurrently filed U.S. patent application Ser. No. 09/766,922, entitled “Optical Reader Having Reduced Parameter Determination Delay,” incorporated previously herein by reference. 
     Optical reader  110  of  FIG. 5   a  also includes programmable control circuit  140  which preferably comprises an integrated circuit microprocessor  142  and an application specific integrated circuit (ASIC  144 ). The function of ASIC  144  could also be provided by field programmable gate array (FPGA). Processor  142  and ASIC  144  are both programmable control devices which are able to receive, output, and process data in accordance with a stored program stored in memory unit  145  which may comprise such memory elements as a read/write random access memory or RAM  146  and an erasable read only memory or EROM  147 . RAM  146  typically includes at least one volatile memory device but may include one or more long term non-volatile memory devices. Processor  142  and ASIC  144  are also both connected to a common bus  148  through which program data and working data, including address data, may be received and transmitted in either direction to any circuitry that is also connected thereto. Processor  142  and ASIC  144  differ from one another, however, in how they are made and how they are used. 
     More particularly, processor  142  is preferably a general purpose, off-the-shelf VLSI integrated circuit microprocessor which has overall control of the circuitry of  FIG. 5   a , but which devotes most of its time to decoding image data stored in RAM  146  in accordance with program data stored in EROM  147 . Processor  144 , on the other hand, is preferably a special purpose VLSI integrated circuit, such as a programmable logic or gate array, which is programmed to devote its time to functions other than decoding image data and, thereby, relieve processor  142  from the burden of performing these functions. 
     The actual division of labor between processors  142  and  144  will naturally depend on the type of off-the-shelf microprocessors that are available, the type of image sensor which is used, the rate at which image data is output by imaging assembly  130 , etc. There is nothing in principle, however, that requires that any particular division of labor be made between processors  142  and  144 , or even that such a division be made at all. This is because special purpose processor  144  may be eliminated entirely if general purpose processor  142  is fast enough and powerful enough to perform all of the functions contemplated by the present invention. It will, therefore, be understood that neither the number of processors used, nor the division of labor there between, is of any fundamental significance for purposes of the present invention. 
     With processor architectures of the type shown in  FIG. 5   a , a typical division of labor between processors  142  and  144  will be as follows. Processor  142  is preferably devoted primarily to such tasks as decoding image data, once such data has been stored in RAM  146 , recognizing characters represented in stored image data according to an optical character recognition (OCR) scheme, handling menuing options and reprogramming functions, processing commands and data received from control/data input unit  139  which may comprise such elements as trigger  174  and keyboard  178  and providing overall system level coordination. 
     Processor  144  is preferably devoted primarily to controlling the image acquisition process, the A/D conversion process and the storage of image data, including the ability to access memories  146  and  147  via a DMA channel Processor  144  may also perform many timing and communication operations. Processor  144  may, for example, control the illumination of LEDs  122 , the timing of image sensor  132  and an analog-to-digital (A/D) converter  136 , the transmission and reception of data to and from a processor external to reader  110 , through an RS-232, a network such as an Ethernet, a serial bus such as USB, a wireless communication link (or other) compatible I/O interface  137 . Processor  144  may also control the outputting of user perceptible data via an output device  138 , such as a beeper, a good read LED and/or a display monitor which may be provided by a liquid crystal display such as display  182 . Control of output, display and I/O functions may also be shared between processors  142  and  144 , as suggested by bus driver I/O and output/display devices  137 ′ and  138 ′ or may be duplicated, as suggested by microprocessor serial I/O ports  142 A and  142 B and I/O and display devices  137 ′ and  138 ′. As explained earlier, the specifics of this division of labor is of no significance to the present invention. 
     Some or all of the above optical and electronic components may be incorporated in an imaging module as are described in commonly assigned U.S. patent application Ser. No. 09/411,936, incorporated herein by reference. 
       FIGS. 5   b - 5   g  show examples of types of housings in which the present invention may be incorporated.  FIGS. 5   b - 5   g  show 1D/2D optical readers  110 - 1 ,  110 - 2  and  110 - 3 . Housing  112  of each of the optical readers  110 - 1  through  110 - 3  is adapted to be graspable by a human hand and has incorporated therein at least one trigger switch  174  for activating image capture and decoding and/or image capture and character recognition operations. Readers  110 - 1  and  110 - 2  include hard-wired communication links  179  for communication with external devices such as other data collection devices or a host processor, while reader  110 - 3  includes an antenna  180  for providing wireless communication device or a host processor. 
     In addition to the above elements, readers  110 - 2  and  110 - 3  each include a display  182  for displaying information to a user and a keyboard  178  for enabling a user to input commands and data into the reader. Control circuit  140  may cause a graphical user interface (GUI) to be displayed on display  182 . A pointer on the GUI may be moved by an actuator or actuators protruding from housing  112 . 
     Any one of the readers described with reference to  FIGS. 5   b - 5   g  may be mounted in a stationary position as is illustrated in  FIG. 5   h  showing a generic optical reader  110  docked in a scan stand  190 . Scan stand  190  adapts portable optical reader  110  for presentation mode scanning. In a presentation mode, reader  110  is held in a stationary position and an indicia bearing article is moved across the field of view of reader  110 . 
     As will become clear from the ensuing description, the invention need not be incorporated in a portable optical reader. The invention may also be incorporated, for example, in association with a control circuit for controlling a non-portable fixed mount imaging assembly that captures image data representing image information formed on articles transported by an assembly line, or manually transported across a checkout counter at a retail point-of-sale location. Further, in portable embodiments of the invention, the reader need not be hand held. The reader may be part or wholly hand worn, finger worn, waist worn or head worn for example. 
     Referring again to particular aspects of the invention, control circuit  140  in the example of  FIG. 4   a  executes a partial frame capture mode in order to clock out and capture pixel data illustrated by valid zone  212 - 1 . Reading the pixel values of valid zone  212 - 1  is effective to decode 1D symbol  216 - 1  in the reader&#39;s full field of view. Given that clocking out and capturing image data of valid zone  212 - 1  consumes less time than clocking out and capturing a full frame of image data, it is seen that execution of a partial frame capture mode decreases the decode time of the reader. In prior art 2D optical readers, electrical signals corresponding to full frame  210  are clocked out in order to decode a single 1D symbol  216 - 1 . The pixels of valid zone  212 - 1  may comprise a single row of pixels (a scan line) or a plurality of rows. 
     In the example of  FIG. 4   b , of control circuit  140  executes a partial frame capture mode in order to capture data defining valid zones  212 - 2 ,  212 - 3  and  212 - 4  of a full frame of image data corresponding to a full field of view of a 2D image sensor. Valid zones  212 - 2 ,  212 - 3  and  212 - 4  are line patterns of image data at various angular orientations. Reading of pixels of line valid zones arranged at various angular orientations is effective to decode a 1D symbol which may be located at an oblique angle in a field of view. It is seen that reading of pixels of line valid zone  212 - 3  will result in the successful decoding of 1D bar code symbol  216 - 2 . Zones  212 - 2 ,  212 - 3  and  212 - 4  may be one or more pixels wide. 
     In the example of  FIG. 4   c , control circuit  140  executes a partial frame capture mode in order to clock out and capture image data defining valid zones  212 - 5  through  212 - 9 . Valid zones  212 - 5  to  212 - 9  form a plurality of horizontal parallel lines. The pattern of valid zones shown in  FIG. 4   c  clocked out and captured in a partial frame capture mode is effective for decoding substantially horizontally oriented 1D symbols which are at an unknown height in a full field of view. It is seen that the reading of image data of valid zone  212 - 8  will not result in the decoding of symbol  216 - 3  because symbol  216 - 3  is not a 1D symbol. Nevertheless, because valid zone  212 - 8  intersects symbol bullseye  216 - 6 , reading of image data of valid zone  212 - 8  may be effective to determine that a 2D symbol is likely present in the full field of view of image sensor  132 . In one aspect of the invention, reader  110  may be configured to switch out of a partial frame capture mode and into a full frame capture mode when reading of image data captured in the partial frame capture mode reveals that a 2D symbol is likely to be represented in the image data corresponding to the image sensor&#39;s full field of view. 
     The states of operation of reader  110  operating in accordance with the invention are normally selected by actuating appropriate buttons of keyboard  178 , or control of a GUI, or by the reading of menuing symbols, as are explained in commonly assigned U.S. Pat. No. 5,929,418 incorporated herein by reference. 
     It should be apparent that several operating states of the invention are possible. In a first operating state, reader  110  is made to operate only in a partial frame capture mode until the time the first operating state is deactivated. 
     In a second operating state, as is alluded to in the example of  FIG. 4   c , the reader operates in a partial frame capture mode until the time that reading of image data captured in the partial frame capture mode reveals that a 2D symbol is likely to be included in the full frame field of view of image sensor  132 . When reading of the partial frame of image data reveals that a 2D symbol is likely to be included in a full frame field of view, control circuit  140  captures at least one full frame of image data from sensor  132  and attempts to decode for the 2D symbol determined likely to be represented in the full frame of image data. A reader operating in the second operating state may also be made to switch to a full frame operating mode on the condition that a symbol is not successfully decoded during operation of the reader in the partial frame operating mode. 
     A third operating state of a reader operating in accordance with the invention is described with reference to  FIGS. 4   d  and  4   e . Operating in accordance with a third operating state, a reader operates in a partial frame capture mode to clock out and capture image data of valid zone  212 - 10  which corresponds to a predetermined pattern and position in field of view  210 . It is seen that reading of image data of zone  212 - 10  will not be effective to decode symbol  216 - 4  because symbol  216 - 4  is of a type of 2D symbol known as a stacked linear bar code. Control circuit  140  may nevertheless detect that symbol is a 2D symbol given that valid zone  212 - 10  intersects a finder pattern  216   f  of symbol  216 - 4 . 
     Sensing that a 2D symbol is likely present in the field of view when reading the partial frame image data corresponding to valid zone  212 - 10 , the reader operating in the third operating state then continues to operate in a partial frame mode to clock out and capture image data that defines a second valid zone  212 - 11  of pixel positions as seen in  FIG. 4   e . The second valid zone  212 - 11  is not of a predetermined size and position, but rather is of an adaptive position whose position, and possibly size, orientation and shape depends on the result of the reading of the image data corresponding to the first valid zone  212 - 10 . Specifically, the second valid zone  212 - 11  is normally at least of a size and position that is likely to encompass the symbol  216 - 5  detected to be present when reading of the image data of first valid zone  212 - 10  (labeled  216 - 4  in  FIG. 4   d ). It is seen that the third operating state is likely to be operative to further reduce the clocking out and capture of irrelevant image data, and therefore is likely to further increase decoding speed. In the third operating state, additional adaptive position valid zones may be clocked out and captured if the reading of image data of first adaptive valid zone  212 - 11  does not result in a symbol being decoded. 
     In the example of  FIGS. 4   f  and  41   g  valid zones  212 - 12  and  212 - 13  correspond to nonlinear groupings of pixels. Capturing of the valid zone patterns  212 - 12  and  212 - 13  of  FIGS. 4   f  and  4   g  is particularly useful for decoding symbol image data in the case that a symbol is likely to be at a certain position in relation to an image sensor&#39;s full frame field of view such as in the center of an image sensor&#39;s field of view as shown in  FIG. 4   f.    
     In the example of  FIG. 4   f  control circuit  140  can successfully decode symbol  216 - 6  because symbol  216 - 6  is located entirely within valid zone  212 - 12 . 
     In the example of  FIG. 4   g , control circuit  140  cannot decode symbol  216 - 7  if operating in the first operating state since symbol  216 - 7  is a 2D symbol and is not entirely located within valid zone  212 - 13 . If operating in the second operating state, then a reader capturing image data within valid zone  212 - 13  may successfully decode symbol  216 - 7  by reading the image data of zone  212 - 13  to determine that a 2D symbol is present, switching operation to a full frame capture mode to capture a full frame  210  of image data, and processing the full frame of image data to decode symbol  216 - 7 . A reader operating in the third operating state described hereinabove may decode symbol  216 - 7 , in the example of  FIG. 4   g , by reading image data within valid zone  212 - 13 , capturing image data within an adaptively defined valid zone (not shown) of sufficient size and position to encompass symbol  216 - 7 , and then processing the image data within the adaptively defined valid zone to decode symbol  216 - 7 . 
     A bar code reading device having an image sensor including a plurality of pixels can be operated to capture a parameter determination frame of image data, wherein the parameter determination frame of image data includes image data corresponding to light incident at less than all of the pixels of the image sensor. A bar code reading device can also be operated in an image capture operating mode in which a partial frame of image data is captured, wherein the partial frame of image data includes image data corresponding to light incident at less all of the pixels of the image sensor, and wherein image data of the partial frame can be processed in order to attempt to decode a bar code symbol. 
     According to its major aspects and broadly stated, the present invention is a method for controlling an optical reader to reduce the reader&#39;s parameter determination delay. According to the invention, an image sensor is adapted to clock out image data from an image sensor according to two modes of operation, a “low resolution” clock out mode of operation and a “normal resolution” clock out mode of operation. 
     In a low resolution mode, some pixels of the reader&#39;s image sensor pixel array are clocked out at a normal clock out speed sufficient to develop electrical signals that accurately represent the intensity of light incident on the pixel array, while other pixels of the array are either not clocked out or are clocked out at a higher clock out rate which is insufficient to allow development of electrical signals that accurately represent the intensity of light at the respective pixels but which nevertheless, result in an increase in the overall frame clock out rate of the frame of image data. In a normal resolution mode of operation the image sensor is caused to clock out electrical signals corresponding to each pixel of the array at a constant “normal mode” speed which is a speed sufficient to ensure that the electrical signal corresponding to each pixel accurately represents the intensity of light incident on the pixel. 
     An optical reader according to the invention operates an image sensor in a low resolution mode of operation in order to clock out and capture a parameter-determining frame of image data at high speed, reads pixel data from the parameter determination frame to determine an operation parameter based on actual illumination conditions, then utilizes the operation parameter in operating an image sensor according to high resolution mode in the clocking out of a succeeding frame of image data that is captured and subjected to comprehensive image data processing which may include image data searching, decoding, and/or recognition processing. Clocking out some of the pixels of an array at high speed during execution of the low resolution mode significantly decreases the reader&#39;s parameter determination delay. 
     These parameters determined by reading pixel values from a low resolution parameter determination frame of image data according to the invention may include an exposure time parameter, an amplification parameter for controlling amplification of an electrical signal prior to its analog to digital conversion, an illumination level parameter (intensity or period of illumination), a dark or light level adjustment parameter and an analog-to-digital converter reference voltage parameter for adjusting the high and/or low reference voltages of the reader&#39;s analog to digital converter. 
     In the present invention, an optical reader image sensor is adapted to clock out image data from an image sensor according to “low resolution” mode of operation in order to reduce a parameter determination delay of the reader. In a low resolution mode, some pixels of the readers image sensor array are clock out at normal clock out speed sufficient to develop electrical signals accurately reflecting the intensity of light at the respective pixel positions, while other pixels of the array are either not clocked out or are clocked out at a higher clock out rate which may be insufficient to allow development of electrical signals that accurately represent light incident on the image sensor&#39;s sensor array but which nevertheless, results in a reduction of the overall frame clock out rate of the frame of image data. An optical reader according to the invention operates in a low resolution frame clock out mode to capture a low resolution parameter determining frame of image data at high speed, reads pixel data from the parameter determination frame to determine an operation parameter based on actual illumination conditions, then utilizes the operation parameter in operating an optical reader. 
     [Beginning of section excerpted from U.S. patent application Ser. No. 09/766,806]. 
     The invention is a method for configuring an optical reader having a 2D image sensor so the reader captures and processes image data at higher speeds. 
     According to the invention, a control circuit of an optical reader equipped with a 2D image sensor is configured to operate in a partial frame operating mode. In a partial frame operating mode, the control circuit clocks out and captures less than a full frame of image data and processes that image data. The control circuit may process the image data of the partial frame, for example, by reading the image data from memory and outputting the image data to an output location such as a display device or a processor system in communication with the reader, by reading and attempting to decode decodable symbols which may be recorded in the partial frame, or by reading and performing optical character recognition on characters represented in the partial frame of image data. 
     In one embodiment, the partial frame operating mode is employed to clock out and capture image data corresponding to at least one linear pattern sufficient so that a 1D symbol in the field of view of the image sensor may be decoded without clocking out and capturing an entire frame of image data. The partial frame of image data that is clocked out from the image sensor during the partial frame capture operating mode may be, for example, a row of pixels at or near the center of the image sensor or a limited number of lines of image data corresponding to pixel locations of the image sensor, possibly at varying angular orientations. The control circuit may be configured so that if the control circuit cannot decode a 1D symbol during the course of operating in the partial frame capture mode, or detects that a 2D symbol is represented in the captured image data, the control circuit switches operation to a full frame capture mode. 
     In another embodiment, the partial frame operating mode is employed to clock out and capture pixel values corresponding to a grouping of pixels at or near a center of an image sensor other than a linear pattern of pixels. This embodiment may be advantageously employed in cases where decodable symbols are expected to be concentrated proximate a center of an image sensor&#39;s field of view. A control circuit may be configured so that if the control circuit cannot decode a symbol represented in the partial frame, or determines that a symbol is represented partially or entirely outside the image data of the partial frame, the control circuit automatically switches operation to a full frame image capture mode. 
     The invention is an optical reader having a 2D image sensor that is configured to operate in a partial frame capture mode. In a partial frame operating mode, the reader clocks out and captures at least one partial frame of image data having image data corresponding to less than all of the pixels of an image sensor pixel array. In one embodiment, the reader operating in a partial frame operating mode captures image data corresponding to a linear pattern of pixels of the image sensor, reads the image data, attempts to decode for a decodable 1D symbol which may be represented in the image data, and captures a full frame of image data if the image data reading reveals a 2D symbol is likely to be present in a full field of view of the 2D image sensor. 
     [End of section excerpted from U.S. patent application Ser. No. 09/766,806]. 
     While the present invention has been explained with reference to the structure disclosed herein, it is not confined to the details set forth and this invention is intended to cover any modifications and changes as may come within the scope of the following claims.