Compact assistive reading device

A compact assistive reading device. A compact form factor is achieved through the use of an optical system with a pin hole aperture, which also obviates the needs for mirrors. One or more light sources are positioned outside the field of view of the optical system. A structure such as a prism film, patterned reflector or light pipe may be used to provide an illumination pattern that enhances the quality of images formed with the optical system. Additionally, processing components to recognize text, numbers or other information on an item placed in the imaging area of the optical system may be incorporated into a housing with the optical system. The housing contains features to facilitate easy insertion of an object into the imaging area and sensors to indicate when the object is properly positioned. The device may function as a currency reader.

BACKGROUND

1. Field of the Invention

The application relates generally to assistive devices for the visually impaired and more specifically to compact assistive reading devices

2. Description of Related Art

Technology has been used to aid the visually impaired perform tasks that many sighted people take for granted. One such approach has been to use a camera to form images of documents or other items. A computer or other device receives the output of the camera and enlarges it for display. Such magnification-based systems are useful only for partially-sighted users.

Assistive devices have also been developed for users who cannot read or extract useful from a display, even if substantially magnified. Such systems have used audio output, such as speech to text converters, to convert items containing text to a form that can be perceived by a visually impaired user. Such converters may be used to enable the visually impaired to access information in books or other documents containing text.

One type of document is currency. In many countries, particularly the United States, all bills of currency are essentially the same size, regardless of denomination. As a result, without an assistive device that can read information printed on a bill, a visually impaired person would be unable to determine the denomination of the bill. Accordingly, currency readers that can recognize and produce a non-visual output indicating a denomination of a bill are known.

SUMMARY

An improved, compact assistive reading device is provided.

In one aspect, the invention relates to a compact apparatus for close-range imaging of an object. The apparatus has a support structure defining an imaging area. A surface with a pin-hole aperture is also supported by the support structure. An imaging array is supported by the support structure such that the surface is positioned with the pin-hole aperture disposed in an optical path between the imaging area and the imaging array. The imaging array is spaced from the imaging area by a distance of less than 25 mm, and at least 100 mm2of the imaging area is focused on the imaging array through the pin-hole aperture. As an example, the separation could be on the order of 15 mm.

In another aspect, the invention relates to a compact apparatus for close-range imaging of an object. The apparatus has a housing having dimensions of less than 100 mm in length, 20 mm in height and 50 mm in width. An imaging array and a planar imaging area are mechanically coupled to the housing. A planar surface having a pin hole aperture is also mechanically coupled to the housing in an optical path between the imaging area and the imaging array.

In another aspect, the invention relates to a method of processing an image representing a bill of currency to detect a non-printed border region. The method may be performed with a processor and includes forming an array of values in a memory coupled to the processor. The values in the array represent successive linear regions parallel to and offset from a side of the image. Each value represents a number of edge points in a respective linear region. As part of the method a value in the array that represents a linear region closest to the side that is above a threshold is identified as a presumptive boundary between a non-printed and printed border region.

The identified non-printed border region may be omitted from the image when processing is performed to identify a denomination of a bill of currency depicted in the image. In some embodiments, this presumptive boundary may be tested to ensure that pixels falling in the presumed non-printed border region can be reliably identified as representing non-printed portions. When a reliable determination is not made, the border region is assumed to be non-existent, which may increase the amount of processing required on the image, but does not degrade accuracy.

DETAILED DESCRIPTION

Applicant has recognized and appreciated that available assistive reading devices can be improved by making such devices compact and easy for visually impaired users to operate. Applicant has further appreciated that an assistive reading device can be made compact through the use of an optical imaging system with a pin hole aperture. Such an optical system may be coupled to a processing system within a compact housing formed with simple input and output devices that make the device easy to operate.

In embodiments in which the assistive reading device reads currency, the housing may be shaped to aid a visually impaired person position a portion of a bill in an imaging area. With a bill properly positioned in the imaging area, the currency reader may acquire and process an image of at least a portion of the bill from which the denomination of the bill can be recognized.

The device may have one or more output devices, such as a speaker or mechanical vibrator, to allow a recognized denomination of a bill to be presented in a audible, tactile or other non-visual format. An output device may also be used to communicate device status, such as to indicate that the device is on or off or that a bill has been correctly positioned in the device for reading.

The device also may have an input device or devices that can be simply operated to allow the user to input commands to control the device, such as commands to power on the device or to provide or repeat an output indicating a denomination of a bill. The input device may also allow a user to provide commands that control the form of the output, such as to turn on or off specific output devices so as to switch between output modes. Other commands may change the volume or intensity of an output indicator, regardless of the output mode used.

FIG. 1illustrates as an example of a compact assistive reading device a currency reader100. Currency reader100has a compact form factor, providing an overall size suitable for carrying the device in a user's pocket. In some embodiments, the currency reader will have a width, W, of a 100 millimeters or less, a length, L, of 50 millimeters or less and a height, H, of 20 millimeters or less. In the embodiment illustrated, currency reader100has dimensions of approximately 74 millimeters by 40 millimeters by 18 millimeters.

Housing110encloses and acts as a support structure for components, such as an optical imaging system and processing components. Additionally, housing110may support one or more input devices or more output devices.

Housing110may be constructed of any suitable material or materials. These materials may be formed into one or more members, suitably shaped to form housing110using any suitable construction techniques. In the embodiment illustrated, some or all of the components of housing110may be molded from plastic using known molding techniques.

The members of housing110may be provided with features that facilitate a visually impaired user firmly grasping currency reader100and/or appropriately orienting currency reader100for use. For example, textured gripping surface112may be formed with a plurality of bumps or projections that can be easily felt by a user. Accordingly, textured gripping surface112provides a mechanism for a visually impaired user to identify the top surface of currency reader100. Similarly textured gripping corners, of which textured gripping corner114A is visible inFIG. 1Aand textured gripping corner114B visible inFIG. 1B, may also be included. As can be seen inFIG. 1A, textured gripping corner114A includes multiple bumps or projections that can be felt by a visually impaired user, allowing the user to identify the rear corners of currency reader100by touch.

Textured surfaces, such as textured gripping surface112and textured gripping corners114A and114B may be formed of the same material used in forming other members of housing110. In some embodiments, the textured surfaces may be integral with other portions of the housing. However, in other embodiments, the textured surfaces may be formed of or coated with materials that enhance gripping of currency reader100. For example, gripping surfaces may be formed with rubberized plastic or may be coated with rubber, vinyl or other relatively soft material that facilitates gripping. Though, the materials used are not critical in the invention and any suitable materials may be used and formed into textured surfaces in any suitable way.

Housing110may also contain other features. For example,FIG. 1Aillustrates a hole118through a corner of housing110. Hole118may be sized for attaching currency reader100to another member, such as a keychain or a lanyard. By attaching currency reader100to such a member, a user may readily carry or locate currency reader100.

In the embodiment illustrated, housing110is formed from at least two members, an upper member110U and a lower member110L. These members may be held together in any suitable fashion. For example, upper housing member110U and lower housing member110L may be held together with screws, adhesive and/or snap fit features. Forming housing110of multiple members allows currency reader100to be assembled by placing an optical imaging system and processing components inside housing110and then fixing upper housing member110U to lower housing member100L. However, any suitable construction techniques may be used.

In the embodiment illustrated, housing110is formed from at least a third member. In the example illustrated inFIG. 1A, housing110also includes battery compartment cover116. Battery compartment cover116may be removably connected to other components of housing110, thereby allowing a battery to be installed within currency reader100after it is manufactured to provide power for operation of the device. Though, any suitable mechanism for supplying power may be used.

In addition to enclosing the optical imaging system and processing components, housing110is adapted for receiving a bill of currency and to support user input devices. In the embodiment illustrated, currency reader100includes user input devices that are easy for a visually impaired user to correctly actuate. In the embodiment illustrated, the user input devices consist of two buttons,120A and120B (FIG. 4A). In the embodiment ofFIG. 1A, buttons120A and120B are positioned in opposing side surfaces of housing110. Also as illustrated inFIG. 1A, each of the buttons has a textured surface, allowing a visually impaired user to locate the button tactilely. In the embodiment illustrated, each button120A and120B performs the same function when pressed, such that a user need not differentiate between button120A and120B to operate currency reader100. Rather, a user may input different commands to currency reader100based on the number of buttons pressed. In this way, a user may input multiple commands to control currency reader100to perform multiple functions through a relatively simple user interface.

As a specific example, depressing either button120A or120B may be interpreted by processing components within currency reader100as a command to initiate a process of determining a denomination of a bill inserted into currency reader100. Pressing both buttons120A and120B simultaneously may be interpreted by the processing components as a command to turn on the device or to change a level of the output. For audible outputs, depressing both buttons may alter the volume of the output. For example, currency reader100may be configured to operate according to one of a set of possible volume levels. Each time buttons120A and120B are pressed together, the device may switch to the next lowest volume level. The volume levels may be arranged cyclically such that when both buttons120A and120B are depressed while the currency reader100is already in the lowest volume level, currency reader100may respond by transitioning to the highest volume level.

In embodiments in which currency reader100supports multiple output modes, the simple push-button interface may be used both to change output levels and output modes. As an example, the output levels may include a mix of volume levels and intensity levels for a mechanical vibrator output device. In such embodiments, depressing both buttons120A and120B when the currency reader100is already operating in the lowest volume setting may result in the device switching to an operating mode in which outputs are represented by vibration pulses of the device. As with volume output levels, multiple vibration output levels could also be defined. In such an embodiment, depressing buttons120A and120B while the currency reader100is already in a vibratory output mode may result in a decrease in the intensity of the vibration pulses.

Regardless of the manner in which a user inputs a command indicating that the denomination of a bill is to be read, to use the device, a user inserts a bill of currency into currency reader100. With the bill in the device, the user may input a command, such as by activating one of buttons120A and120B, to specify that currency reader100should read the denomination of the bill and produce a non-visual output indicating that denomination.

For currency reader100to read the denomination of a bill, a feature of the bill indicative of its denomination is positioned within currency reader100in an imaging area of an optical imaging system. To facilitate such positioning of a bill, housing110is formed with a slot130sized to receive a bill of currency and guide at least a portion of the bill into an imaging area.

As illustrated inFIG. 1A, slot130may be shaped to facilitate insertion of a bill of currency by a visually impaired user. As shown, slot130has a protruding floor132, forming a shelf on which a user may rest a forward edge of a bill of currency. With the bill of currency resting on floor132, a user may push it towards the rear of housing110, forcing the front edge of the bill of currency under upper edge136. Once the forward edge of the bill of currency is under upper edge136, the forward edge is fully enclosed within slot130and, as the user presses the bill further towards the rear edge of housing110, the bill will be guided into position in the imaging area of the optical imaging system within housing110.FIG. 1Billustrates a bill of currency150inserted into slot130.

To further facilitate insertion of a bill of currency, side walls134A and134B in the areas adjacent floor132are tapered. As can be seen inFIG. 1A, the tapering of sidewalls134A and134B creates a wider opening to slot130at the forward edge of floor132than adjacent to upper edge136. This tapering facilitates placement of the forward edge of a bill of currency against floor132while constraining the position of the bill of currency when it is fully inserted into slot130. Though, it should be appreciated that, while the structure illustrated of slot130facilitates use of currency reader100by a visually impaired user, any suitable mechanism for receiving a bill of currency may be used.

In some embodiments, insertion of a bill of currency into an assistive reading device may cause the device to power on. Such an embodiment may be implemented, for example, by incorporating a sensor adjacent the opening of slot130. Such a sensor may be implemented as a switch, capacitive sensor, magnetic sensor or other suitable type of sensor. When the sensor detects the presence of a bill in slot130, it may power up the device, preparing the device to recognize a denomination of a bill without requiring a user to expressly power on the device. Though, in some embodiments, the device does not attempt to recognize that a bill is improperly inserted into the device, which may be ascertained from one or more position sensors within the device. Audible tones may be used to provide feedback to a user by indicating when a bill is detected in slot130and whether the bill is properly positioned for imaging a predetermined area of the bill. In embodiments in which a sensor is included to detect the presence of a bill, a recognition process may begin automatically once the bill is determined to be properly positioned.

FIG. 2Aschematically illustrates bill150positioned within slot130in housing110. As can be seen inFIG. 2A, each corner of bill150, such as corners252A and252B, contains a numerical designation of the denomination of bill150. Though not shown inFIG. 2A, within housing110an optical imaging system is positioned relative to slot130such that, when bill150is fully inserted into slot130a corner of bill150will be adjacent an imaging area of the optical imaging system. In this way, a corner of bill150including a numerical designation of the denomination of the bill will be in the imaging area of the optical imaging system when the bill150is fully inserted in slot130. Though, it should be appreciated that the portion of the bill in the imaging area need not include a numerical designation. Any portion of the bill that has recognizable characteristics may be placed in the imaging area and the denomination of the bill may be determined based on matching that portion of the bill to a template associated with a specific bill denomination or otherwise determining that the characteristics are present in the imaging area.

In the embodiment illustrated, currency reader100includes one or more position sensors that can detect the position of bill150and ascertain when it is fully inserted into slot130. The outputs of the position sensors may be used in any suitable way. For example, the position sensors may be coupled to processing components within currency reader100and used to trigger a process of reading the denomination of bill150. The processing components, for example, may capture an image of the imaging area in response to an indication from the position sensors that bill150is fully inserted into slot130(FIG. 1). Alternatively, processing components may output an indication to a user that bill150has been properly positioned within slot130in response to the outputs of the position sensors. Such an output indication may prompt a user to activate input devices for currency reader100that cause the processing components to capture an image and identify a denomination of bill150. As a further alternative, the outputs of the position sensors may be used to generate an output that serves as a warning to a user that the bill is not properly positioned in the housing when the user inputs a command to read the denomination of the bill. Thus, the specific manner in which the outputs of position sensors are used as part of a process of reading a denomination of bill150is not critical to the invention and they may be used in any suitable way.

In the embodiment illustrated inFIG. 2A, three position sensors, position sensors210A,210B and210C, are included within currency reader100. Each position sensor is mounted within housing110such that it will be adjacent an edge of bill150when bill150is correctly positioned within slot130(FIG. 1A).

As illustrated, position sensor210A is mounted within housing110in a location that corresponds with a side edge of bill150when the bill is correctly inserted into slot130. Position sensors210B and210C are mounted within housing110such that they will detect the forward edge of bill150when the bill is properly inserted into slot130. With this mounting of position sensors210A,210B and210C, when all three sensors output an indication of the presence of bill150, processing components in currency reader100can determine that bill150is properly positioned for reading.

In the embodiment illustrated inFIGS. 2A and 2B, position sensors210A and210B and210C may be optical position sensors.FIG. 2Cillustrates a possible instruction of such optical position sensors. Each position sensor may include a light source212and a light sensor214. As an example, light source212may be a light emitting diode (LED) and light sensor214may be a photo transistor. However, any suitable components may be used as a light source and/or a light sensor, including, as one example, an optical fiber guide that directs light to the primary imaging array rather than dedicated light sensors.

As shown, light source212may be directed at a smooth surface of housing110. Light sensor214may be directed generally at the same location of housing110. When no bill is present, light from light source212reflects from the smooth surface of housing100and is detected by light sensor214. If a bill150is present in slot130, less light will reflect from the bill than reflects from the surface of housing110. Accordingly, the amount of light measured by sensor214decreases when a bill is inserted between sensor210and housing110. Processing components coupled to position sensor210may, therefore, detect the presence of a bill positioned within slot130based on the level of light sensed by light sensor214. Though, any suitable position sensors may be used, including, for example, electromechanical switches, capacitive sensors or magnetic sensors.

Regardless of the type of position sensors used, the position sensors may be arranged within the housing to detect when the bill is in position for reading the denomination of the bill. In the example illustrated, when bill150is properly positioned, corner252A is positioned in an imaging area230of an optical system within housing110.FIG. 2Bshows this positioning.

FIG. 2Billustrates housing110from the prospective of line B-B inFIG. 2A. InFIG. 2B, housing110is shown in outline form to reveal the positioning of some of the components inside housing110.

FIG. 2Billustrates that the floor of slot130under upper edge136contains a transparent window232. In the embodiment illustrated, transparent window232is formed of a transparent member, such as a plastic or glass sheet. However, any suitable material may be used to form window232, and in some embodiments, a transparent window may be formed as an opening within the material used to form housing110without any member inserted in the opening.

Regardless of the material used to form window232, window232provides an imaging area230for an optical system within housing110. In the embodiment illustrated, window232is positioned such that corner252A of bill150is positioned in imaging area230when bill150is properly aligned within slot130.

In the embodiment illustrated, a compact optical system is formed using a pin hole aperture. Such an optical system may include an aperture plate220containing a pin hole aperture224. The pin hole aperture224may be between imaging area230and an imaging array222. In this way, an image of an object, such as the corner of a bill150, within imaging area230may be focused on an imaging array222. Imaging array222may then capture an image of the object for further processing.

Imaging array222may be an imaging array as is known in the art. For example, imaging array222may be an array of charge coupled devices that can be connected to other processing components within currency reader100. However, a CMOS sensor array or any other suitable form of imaging array may be used.

Turning toFIG. 3, a schematic illustration of components of currency reader100is provided. In the embodiment illustrated, processing is provided in a processor, such as microcontroller310. As illustrated, microcontroller310includes embedded memory312in which a program may be stored. The program may control microcontroller310and, hence, other components of currency reader100, to perform operations that result in determining denomination of a bill of currency.

As shown, microcontroller310is coupled to position sensors210A,210B and210C. As a result of these connections, a program stored in memory312may include conditional operations that depend on whether position sensors210A,210B and210C produce outputs indicating that a bill is properly positioned within slot130. This conditional operation may include, for example, outputting a warning to a user that a bill is not properly positioned when the user inputs a command to read the denomination of a bill. Alternatively, these conditional operations may include triggering a process that captures an image of at least a portion of a bill inserted into slot130when the outputs of position sensors210A,210B and210C indicate that the bill is properly positioned.

The program for microcontroller310may also include conditional operations that are based on user inputs. As shown inFIG. 3, switches320A and320B are also coupled to microcontroller310. Switches320A and320B are positioned behind buttons120A and120B, respectively. Accordingly, when a button120A or120B is depressed by a user, its corresponding switch will momentarily change state, producing a signal that can be detected by microcontroller310. In this way, microcontroller310may be programmed to respond to user inputs through buttons120A and120B.

FIG. 3also indicates that imaging unit330is coupled to microcontroller310. Image unit330may include imaging array222on which an image of corner252A is focused by pin hole aperture224(FIG. 2B). The connections between microcontroller310and image unit330may include both control and data paths. Using these paths, when microcontroller310determines, based on the signals received from switches320A or320B and signals from position detectors210A,210B and210C that the denomination of a bill is to be read, microcontroller310may generate outputs acting as control inputs to image unit330. These control inputs may cause imaging array224to capture an image and output data representing the pixels of that image to microcontroller310.

Microcontroller310may perform one or more algorithms on that image data to determine the denomination of the bill inserted into slot130(FIG. 1A). Such processing may be performed in any suitable way. In some embodiments, a denomination may be detected by performing a cross correlation between groups of pixels in the captured image and prestored set of templates representing unique patterns printed on currency of specific denominations. In some instances, the unique patterns may include all or a portion of a numeral representing a denomination of the bill. Though, it is not a requirement that the pattern be a numerical indicator. A template in the set with a high cross correlation to the captured image may be regarded as matching the denomination of the bill. In this way, the denomination associated with the matching template may be output to a user as the denomination of the bill.

Regardless of the specific mechanism used to determine the denomination, the determined denomination may be output to the user through any one or more suitable output devices. In the embodiment shown inFIG. 3, two output devices are illustrated, speaker340and mechanical vibrator350. Here, speaker340is used to output an audible indication of the recognized denomination. Vibrator350is used to cause currency reader100to vibrate in pulses, with the pattern of pulses signaling the determined denomination. For example, one pulse may signal a one dollar bill; two pulses may signal a 2 dollar bill; three pulses may signal a five dollar bill; etc. However, any suitable pattern of pulses may be used.

To generate the vibration pulses, currency reader100may include a driver352that powers vibrator350in response to a control signal generated by microcontroller310. Driver352and vibrator350may be components as known in the art. Though, any suitable components may be used.

The audible output produced by speaker340may likewise be in the form of a series of pulses—though audible. Speaker340may output a series of blips or other sounds representing the detected denomination of a bill. Though, an audible output may be encoded in other ways to signify the denomination of a bill. For example, tones of different frequency may signal different denominations. In other embodiments, speaker340may output an indication of the detected denomination using synthesized speech. In such an embodiment, microcontroller310may be programmed to output a signal that, when applied to speaker340, produces speech.

In the embodiment illustrated, microcontroller310outputs a stream of digital bits using pulse code modulation. That stream of bits is applied to digital-to-analog converter342. The output of digital-to-analog converter342is filtered in audio filter344and applied to an audio amplifier346. As shown, audio amplifier346drives speaker340. In this way, by appropriately programming microcontroller310to generate a digital stream in a suitable pattern, the format of the audio output may be controlled.

Microcontroller310may also be programmed to perform other operations associated with reading denomination of a bill. For example, currency reader100may include a source of illumination332directed at imaging area230(FIG. 2B). To conserve power, illumination source332may be turned on only when imaging array222is to capture an image. Accordingly, illumination source332may be coupled to microcontroller310through a driver334. Driver334may be configured to only supply power to illumination source332when microcontroller310asserts a control line indicating that an image is to be captured.

Other components of currency reader100are also illustrated inFIG. 3. Power for operation of the electronic components may be supplied by a battery360. Appropriate power levels may be supplied through a voltage converter362. As shown, voltage converter362provides power from battery360to microcontroller310, switches320A and320B, imaging array330, driver334, digital-to-analog converter342, amplifier346and driver352.

FIG. 3also illustrates a download and test port370may be included. Such a port may allow a program to be downloaded into memory312. Such a port may also allow test signals to be coupled to and from microcontroller310to test operation of currency reader100.

The circuitry illustrated inFIG. 3may be implemented using commercially-available electronic components. However, the circuitry may be implemented in an Application Specific Integrated Circuit (ASIC) or a programmable device, such as a gate array. Accordingly, any suitable components may be used.

In some embodiments, the components may be packaged to facilitate compact construction of currency reader100. As an example, multiple components illustrated inFIG. 3may be fabricated on a single printed circuit board. For example, microcontroller310, driver334, digital-to-analog converter342, audio filter344, amplifier346and voltage converter362may be attached to and interconnected through the printed circuit board. Other components may be mounted to other locations within housing110and interconnected to the printed circuit board using wires, flex circuits or other suitable means.

FIG. 4Ashows a possible layout of such components to achieve a compact arrangement. InFIG. 4A, housing110is shown in outline form. Printed circuit board410is shown mounted in one corner of housing110. As shown, speaker340is mounted to a floor of housing110. As shown, switches320A and320B are positioned adjacent buttons120A and120B. A possible position for battery360is also illustrated.

As can be seen, imaging unit330is positioned to align with window232. Illumination source332is positioned to illuminate window232. Though any suitable positioning may be used, in the embodiment illustrated, the illumination source is placed outside the field of view of the imaging unit. The inventor has recognized and appreciated that this positioning limits reflection of the light source from the window, reducing interference with the image. By reducing interference, the recognition task may be simpler and more accurate. In the embodiment illustrated inFIG. 4A, illumination source334is implemented as two light emitting diodes, LED434A and434B.

FIG. 4Bshows the structure ofFIG. 4Afrom the perspective of line B-B inFIG. 4A. As can be seen inFIG. 4B, printed circuit board410is mounted, such as through mounting members430A and430B, to a top surface of currency reader100. Speaker340is mounted to a lower surface. This mounting leaves a space through which light from LEDs434A and434B may pass to reach window232.

FIG. 5Aprovides an alternative view of components inside housing110of currency reader100.FIG. 5Ashows a cross section through currency reader100. In the embodiment illustrated inFIG. 5A, window232is set back from the surface of housing110defining slot130, creating a recess530. Recess530prevents a bill150from sliding across an upper surface of window232when inserted in slot130. Accordingly, recess530may improve the accuracy of currency reader100by preventing scratching of window232by contaminants on bill150. By avoiding scratches or other contamination of window232, a more accurate image of bill150may be captured.

FIG. 5Aalso illustrates a further feature that may be incorporated to improve the accuracy of currency reader100. As illustrated, a patterned reflector is included adjacent window232. Patterned reflector520is positioned to reflect light from LEDs434A and434B towards window232. Patterned reflector520is positioned to compensate for uneven illumination across window232caused by LEDs434A and434B being positioned to illuminate window232from an oblique angle.

As shown, LEDs434A and434B will provide greater direct illumination at the side of window232closest to LEDs434A and434B. Patterned reflector520is positioned to reflect light to preferentially illuminate the side of window232that is farthest from LEDs434A and434B. In this way, the combination of illumination directly from LEDs434A and434B and illumination reflected from patterned reflector520may be relatively constant across window232.

FIG. 5Bshows a cross section of currency reader100similar to that shown inFIG. 5A. The cross section ofFIG. 5Bdiffers from that inFIG. 5Aand that it is taken through a different section of currency reader100.

FIG. 6Aillustrates operation of the patterned reflector520. As shown, LEDs434A and434B are positioned at an oblique angle relative to window232behind which an object, such as bill150is positioned. As can be seen, the rays of light from LEDs434A and434B that illuminate different portions of window232can have different properties, tending to cause variations in illumination across window232. For example, ray660A illuminating the edge of window232closest the LEDs434A and434B travels a shorter distance and strikes window232at a less oblique angle than ray660B that illuminates the farther edge of window232. In such a configuration, ray660B may provide less intense illumination than ray660A.

To compensate for differences in direct illumination, patterned reflector620is positioned such that a portion of the light emitted by LEDs434A and434B strikes patterned reflector620and is reflected, such as in ray662towards window232. The combination of illumination directly from LEDs434A and434B and that reflected from patterned reflector620combines to provide a more uniform illumination of window232than could be provided by light from LEDs434A and434B alone.

As shown, the patterned reflector620can compensate, at least partially, for variations in illumination across window232based on distance from LEDs434A and434B. In addition to variations in illumination associated with distance, variation in illumination may also occur across window232as a result of angular direction. For example,FIG. 4Ashows beams from LEDs434A and434B illuminating window232. Points668A and668B are both at substantially the same distance from the source of illumination. However, point668A is closer to the beam center than point668B. Accordingly, illumination at point668A may be more intense than at point668B.

To compensate for this difference in intensity based on angular direction, patterned reflector620may have a pattern that reflects different amounts of light, depending on the angle relative to the beams emitted by LEDs434A and434B.FIG. 6Billustrates a possible pattern.FIG. 6Bshows a front view of patterned reflector620, which is in contrast to the side view inFIG. 6A. As shown, patterned reflector620has different reflectivity at different locations on its surface. This pattern of reflectivity may be selected to provide more reflectivity at beam angles where less illumination is received and less reflectivity at beam angles where greater illumination is received. Accordingly,FIG. 6Billustrates that patterned reflector620has a central portion670that is less reflective than side portions672and674. As shown, the amount of reflectivity may vary continuously across the surface of patterned reflector620.

Though not expressly illustrated inFIG. 6B, other variations may be incorporated into the reflectivity pattern of patterned reflector620to compensate for other variations in the intensity of the illumination. For example, the reflectivity of patterned reflector620may vary across the surface of patterned reflector620from bottom676to top678.

Enabling relatively uniform illumination from an oblique angle as illustrated inFIG. 6Aallows for a compact design of an assistive reading device, particularly in combination with an optical imaging system incorporating a pinhole lens. As illustrated, an optical imaging system using a pinhole lens can provide a relatively large field of view that spans an angle, A. As a result, window232maybe in the field of view of the imaging system, even though imaging array222is spaced from window232by a distance D1, which can be relatively small. Distance D1may be less than the height of currency reader100, and in some embodiments may be a substantial factor in defining the height of the device.

FIG. 7provides examples of dimensions of an optical imaging system employing a pinhole lens that may lead to a compact assistive reading device. In the example ofFIG. 7, imaging area230is on the order of 1 in2. As a specific example,FIG. 7illustrates that imaging area230is 0.94 in. An imaging array222is on the order of 0.1 in2. In a specific example ofFIG. 7, the imaging array222is 0.09 in2. As shown, imaging array222is separated from aperture plate220by a distance of 0.04 in. This separation provides a field of view in excess of 75 degrees. In the example ofFIG. 7, the field of view is 83.7 degrees. With this field of view, an image of items in imaging area230may be focused on imaging array222with a separation between imaging area230and imaging array222on the order of one half in. In the example ofFIG. 7, the separation D10.56 in.

Though the specific dimensions ofFIG. 7are illustrative rather than limiting of the invention, they demonstrate a suitable implementation of a compact assistive device.

FIG. 8illustrates an alternative embodiment of imaging components in a compact assistive reading device. The embodiment ofFIG. 8includes a pinhole optical imaging system, which may be formed from an aperture plate220with a pinhole224focusing images of objects in an imaging area onto an imaging array222. As in the embodiment ofFIG. 6A, the imaging area230is illuminated from an oblique angle. In the example ofFIG. 8, imaging area230is illuminated by a light emitting diode (LED)834. Though, any suitable illumination source may be used.

As shown, LED834directs a beam of light generally at the center of imaging area230. To increase the uniformity of illumination cross imaging area230, a refractive element may be positioned in the path of the beam of light. A refractive element can redirect the beam of light from LED834to impinge on window232in a substantially perpendicular direction. With this incident angle, more of the light from LED834is directed into imaging area230, increasing both the intensity and uniformity of the illumination across imaging area230. In the embodiment illustrated, the refractive element is a prism film832applied to a lower a surface of window232. Prism film is known in the art and suitable prism film may be commercial procured. However, any suitable refractive element may be used.

FIG. 8does not illustrate a reflector perpendicular to window232, such as pattern reflector620(FIG. 6A). However, a reflector may be incorporated into the design ofFIG. 8and that reflector may be patterned as illustrated inFIG. 6Bor with any other suitable pattern to provide uniform illumination across imaging area230.

FIG. 9illustrates an alternative embodiment of an imaging system that may be employed in a compact assistive device. In the embodiments ofFIG. 6AandFIG. 8, imaging array222is oriented parallel to window232defining imaging area230.FIG. 9illustrates an alternative embodiment in which imaging array222is also positioned at an oblique angle relative to imaging area230.

Though not a requirement of the invention, in the embodiment illustrated inFIG. 9, aperture plate220is mounted perpendicular to window232defining imaging area230. As shown, aperture plate220is positioned to the same side of imaging area230as LED834. However, aperture plate220is positioned out of the path of a beam emanating from LED834.

Imaging array222is positioned behind aperture plate220such that pinhole224in aperture plate220is in the optical path of light reflected from imaging area230that is focused by pinhole aperture224. In the embodiment illustrated, imaging array222is mounted at an angle B. Mounting imaging array222at an angle can compensate for distortion caused by having the imaging array at an oblique angle.

For example, as illustrated inFIG. 9, a ray, such as ray960A, reflected from a near portion of imaging area230, such as region970A, travels a relatively short distance to imaging array222, which would tend to cause items in region970A to appear larger than items in region970B that are farther from imaging array222. However, as can be seen from the path of960B, representing a reflection from an object in region970B, the tilt of imaging array222ensures that ray960B has a longer path from pinhole224to imaging array222than does ray960A. A longer path from the pinhole224to the imaging array222tends to introduce magnification into the image. Accordingly, the tilt angle B of imaging array222may be selected such that demagnification associated with objects in region970B in comparison to objects in region in970A is offset by the apparent magnification of objects imaged at region972B of imaging array222relative to those objects imaged in region972A. In this way, a relatively uniform magnification across imaging area230may be provided, which can facilitate accurate identification of objects in imaging area230, even though the optical system is relatively compact.

In the embodiment ofFIG. 9, placing imaging array222to the side, rather than parallel and facing window232, may allow a decrease in the height of an assistive reading device. For example,FIG. 9illustrates that the distance in the space dimension required to accommodate both an illumination source and imaging system is D2. In some embodiments, the distance D2may be less than the distance D1(FIG. 8) when the imaging array is parallel to window232.

Other than the positioning of aperture plate220and imaging array222, the components used in forming the assistive reading device illustrated inFIG. 9may be the same as described above in connection with the embodiments ofFIG. 6AorFIG. 8. Though, any suitable components may be used.

In the foregoing examples, principles for making a compact assistive reading device have been illustrated embodied in a currency reader. Though, the invention is not so limited. The invention may be employed for reading numbers or letters or recognizing other symbols on paper or other planar objects that may be placed in an imaging area.FIG. 10Aillustrates a planar object1050placed on a housing1010with a window232. Window232exposes a portion of object1050, allowing an image of the portion to be focused by pinhole224onto imaging array222. Processing of the image captured on imaging array222may be performed in components as described above in connection withFIG. 3. To accommodate processing of objects other than currency, the programs stored in memory312may, rather than recognizing indications of denominations of bills of currency, may be adapted to recognize text, numbers or other symbols that may appear on object1050. Though any suitable processing components may be used.

FIG. 10Bis a cross-sectional view of the embodiment ofFIG. 10A. In the embodiment ofFIG. 10A, portions of housing1010are not illustrated for clarity. In the embodiment ofFIG. 10B, housing1010is illustrated as having members that position and support aperture plate220and imaging array222for appropriate imaging of the imaging area created by window232. In the embodiment illustrated, housing1010, in addition to having a surface in which window232is formed, contains members1012that define the position of aperture plate220. Members1012may also define the position of a substrate1014that positions and supports imaging array222. In the embodiment illustrated, the members of housing1010that position and support other components of the assistive reading device may be integrally formed with the member in which window232is formed. Such an embodiment may be implemented by forming the support members of housing1010in the same molding operation as the outer surfaces of the housing. However, it is not a requirement that the support members be integrally formed, and any suitable construction techniques may be used.

FIG. 10Cillustrates that the techniques for forming a compact assistive reading device are not limited to use in constructing assistive devices that read text, numbers or other symbols on flat objects, such as paper or bills of currency.FIG. 10Cillustrates that three-dimensional objects, such as objects1060A and1060B, may be positioned in an imaging area adjacent to window232such that imaging array222may capture an image of those objects. Objects1060A and1060B may be objects such as pills or hearing aide batteries that contain text, numbers or symbols. Alternatively or additionally, the objects1060A and1060B may be shaped or have features that a visually impaired person may not be able to perceive without assistance. Though, an assistive device may be configured to recognize any suitable types of objects, including objects from mainstream use, other than objects a visually impaired person may seek to recognize. The images captured with imaging array222in the embodiment ofFIG. 10Cmay be processed using components as illustrated inFIG. 3or any other suitable components. Though, the program stored for micro-controller310maybe adapted to recognize characteristics of objects1060A and1060B. Those characteristics may include the shape, size, presence or absence of certain features, the orientation of the objects on window232or other suitable characteristics. The components ofFIG. 3may be adapted to output an indication of whether such characteristics are detected. Though, in some embodiments, a port, such as port370may be used to output an enlarged image of all or a selected portion of the objects. The image may be output in digital form and magnified for display on a separate display device.

FIG. 11illustrates yet a further alternative embodiment of an assistive reading device using pinhole optics. As shown, the embodiment ofFIG. 11includes an aperture plate220and imaging array222. In the embodiment ofFIG. 11, a solid state optical chamber1110is positioned between the illumination source and window232defining the imaging area. Optical chamber1110acts as a light pipe to direct illumination from the illumination sources towards window232.

As is known in the art, an optical chamber may be formed using solid state elements that have surfaces defining the boundaries of the optical chamber. The surfaces of the solid state elements are positioned relative to the source of illumination and also relative to materials of different refractive index such that light emanating from the illumination source is reflected from those surfaces towards its intended destination, here window232. In the example ofFIG. 11, optical chamber1110includes, for example, a surface1112positioned such that light from LED1134striking surface1112will be reflected towards window232. Though, it is not a requirement that the surfaces of optical chamber1110directly reflect the light towards window232. For example, light from LED1134may impinge on surface1114and be reflected to patterned reflector260. From patterned reflector260, the light may be reflected to window232. Accordingly, many configurations of optical chamber1110are possible for providing suitable illumination across window232.

FIG. 11illustrates a further variation that is possible in some embodiments.FIG. 11illustrates two light sources, LED1134and LED1136. In some embodiments, two light sources emitting light across substantially the same spectrum may be used. The two light sources may be spatially separated to improve the uniformity of the illumination across the imaging area. For example, two LEDs that emit visible light may be used. In such an embodiment, both sources of illumination may be activated simultaneously when an image is to be captured with imaging array222.

In other embodiments, multiple sources of illumination may be used, with different sources emitting light in different spectra. For example, LED1134and LED1136emit light in different spectra. LED1134may be a visible light source and LED1136may be an infrared light source. These sources of illumination may be operated at different times, such that multiple images of an object are captured, each formed based on illumination of a different spectra. In some embodiments, additional information about an object under inspection may be obtained by processing multiple images.

As an example, certain characteristics of a bill of currency may be more easily detected in an image when the bill is illuminated with infrared light than with visible light. In such a scenario, the denomination of a bill of currency may be more accurately recognized by an image analysis algorithm that computes a probability that the features that are more visible when illuminated by infrared light appear in an image captured by imaging array222while LED1136is illuminated. The imaging algorithm may also compute the probability that features that are more visible in visible light are present in an image captured by imaging array222while LED1134is turned on. The analysis algorithm may then compute a weighted probability indicating whether a bill of a specific denomination is present in the imaging area by combining these two probabilities. However, any suitable algorithm may be used to control multiple sources of illumination such as LEDs1134and1136and to process images acquired when those light sources are turned on.

FIGS. 12A and 12Billustrate an alternative embodiment of a compact currency reader. In the embodiment illustrated, an optical system and processing components are packaged in a housing1210shaped to form a key fob1200. The optical components may include pinhole imaging system and a light source that illuminates an imaging area from the side, such as inFIG. 6A,8or9. Such components may be used to form a compact device, which has dimensions such as 30 mm by 25 mm by 10 mm. Buttons, such as buttons1220A and1120B may be incorporated at any suitable location on housing1210. As with embodiments described above, buttons1220A and1220B may serve as an input device for a user of the assistive reading device ofFIG. 12A. One or more output devices (not shown) may be incorporated within housing1210. The output devices may include a speaker and/or a mechanical vibrator to produce output in an audible or tactile form.

FIG. 12Billustrates that the assistive reader ofFIG. 12Ais sized to receive only one corner or a bill150. Though, other embodiments are possible.

Turning toFIGS. 13A. . .13E, a further embodiment is illustrated. In the embodiment ofFIGS. 13A. . .13E, an assistive device is attached to a portable electronic device that includes an imaging array and processing components that can be programmed to perform functions of an assistive reading device. Such a portable electronic device may also include input and output devices though which commands to control operation of the assistive reading device can be supplied by a user and output can be presented to the user.

As one example of a portable electronic device that may be used to form an assistive reading device, a cell phone1300is illustrated. As is known in the art, a cell phone may include a camera that can capture images. InFIG. 13A, lens1302of such a camera is illustrated. Cell phone1300may include input and output devices, such as buttons and a speaker and/or mechanical vibrator. However, for simplicity, those components are not illustrated inFIG. 13A

FIG. 13Billustrates that an optical unit1310may be attached to cell phone1300to form an assistive reading device. Optical unit1310is positioned on cell phone1300such that an object placed in an imaging area of optical unit1310is projected through lens1302onto the imaging array of the camera within cell phone1300. To facilitate positioning of optical unit1310, optical unit1310is formed with a housing that includes attachment members, illustrated inFIG. 13Bas attachment members1316. Attachment members1316may have a fixed shape adapted to conform to a housing of cell phone1300. Alternatively, attachment members1316may have an adjustable shape that can be adjusted to conform to a housing of cell phone1300, thereby securing optical unit1310in position relative to camera1302(FIG. 13A).

The housing of optical unit1310has an upper portion1312and lower portion1314, separated to define a slot1330(FIG. 13C). As with the embodiment of an assistive reading device isFIGS. 12A and 12B, slot1330is configured to receive a corner of a bill of currency for which the denomination is to be recognized. Lower portion1314may include one or more illumination sources to illuminate an object to be imaged. In addition, lower portion1314may contain a support structure that positions a pinhole in an aperture plate such that the pinhole acts as a lens focusing an image of an object placed in slot1330through lens1302onto an imaging array1322within cell phone1300. Such a configuration is illustrated inFIG. 13C, which represents a cross section of the configuration inFIG. 13Btaken along the line C-C.

As can be seen inFIG. 13C, an upper surface of lower portion1314is formed with a window1332. An aperture plate1340, in the embodiment illustrated, is placed parallel to window1332.

FIG. 13Dshows an enlarged version of the optical system illustrating focusing provided by pinhole1344in aperture plate1340. As can be seen inFIG. 13D, light reflected from an object placed into slot1330may be focused by pinhole1344onto lens1302. Lens1302may then focus that light into an image on imaging array1322. Components within cell phone1300may capture that image from imaging array1322and process it using techniques as described above or in any other suitable way.

Light for forming such an image may be provided by a source of illumination within optical unit1310. For example, LEDs1334A and1334B are illustrated (FIG. 13E). As in embodiments described above, multiple illumination sources may be used to provide uniform illumination across window1332or maybe used to allow images based on different illumination spectra to be captured.

In some embodiments, it may be desirable to allow adjustment of the position of aperture plate1340as a way to define the spacing between pinhole1344and lens1302. Changing the spacing may adjust the focus of optical unit1310. In the embodiment illustrated inFIGS. 13D and 13E, an adjustment mechanism is provided. By configuring aperture plate1340in a generally circular shape, threads1346may be formed in an outwardly directed ends of circular aperture plate1340. Complimentary threads1348may be formed on a member of lower portion1314. As a result of the threaded engagement between aperture plate1340and lower portion1314, rotation of aperture plate1340will cause aperture plate1340to ride along the threads, thereby changing the separation between frame1342, defining the lower surface of optical unit1310and aperture plate1340

FIG. 13Eillustrates an adjustment mechanism that may be used to used to rotate aperture plate1340such that spacing between pinhole1344and lens1302is adjusted. In the embodiment ofFIG. 13E, the adjustment mechanism is a lever1350that extends outside the housing of optical unit1310. Lever1350is coupled to aperture plate1340such motion of lever1350causes rotation of circular aperture plate1340. However, any suitable mechanical or motorized mechanism may be used to alter the position of aperture plate1340.

Regardless of whether and what mechanism is used to focus an image of an object on to an imaging array, the image may be captured from the array as a series of pixels, each representing an intensity value at a point in the image. Those pixel values may then be processed to recognize the denomination of a bill of currency or other symbol or object that may be present in the image. That processing may be performed in any suitable processing components, such as microprocessor310ofFIG. 1or a microprocessor within a cell phone1300ofFIG. 13A.

Regardless of the specific component that performs this processing,FIG. 14illustrates a process that may be used to identify a denomination of a bill of currency.

FIG. 14illustrates a method of operation of a processing system, such as that illustrated inFIG. 3. The process ofFIG. 14begins at block1410where the system is initialized. Initialization may occur in response to the device being powered on or other event, such as a user depressing a button, such as button120A or120B. Regardless of the triggering event, the system may be initialized in any suitable way. Initialization may be performed using techniques as known to those skilled in the art of digital circuit design. Such initialization may include storing values in memory locations that are used during computations that lead to identification of denomination of a bill of currency.

Once the system is initialized, processing may proceed to block1420where the system monitors for a button to be pressed by a user. When a button press is detected, processing may proceed to decision block1422. At decision block1422, processing may branch depending on the context of the button press detected at block1420. In the embodiment illustrated inFIG. 1, an assistive reading device contains two buttons. In the process ofFIG. 14, if both buttons are pressed simultaneously, the button press signals that the volume is to be adjusted. Accordingly, processing branches from decision block1422to block1424. At block1424, the volume and/or mode of operation of the device is changed. When both buttons are pressed simultaneously, each button press may signify that the volume is to be decreased by one level. When the volume is at its lowest level, depressing both buttons may cause the device to switch output modes, providing outputs as vibratory pulses rather than audible tones.

In addition to changing the volume/mode, processing in response to a button press at block1424may include other operations, such as outputting a tone or other indication for a user that the button press was detected, regardless of the specific processing performed at block1424. Once that processing is completed, the process loops back to block1420and awaits further input. The process may continue in this loop until a command is received indicating another operation is to be performed.

In the embodiment illustrated, other commands may be signaled by a user depressing a single button. When a single button press is detected, the process will branch from block1422to block1430. At block1430, the system may be calibrated based on information captured periodically while the system is not in use. In some embodiments, a surface of the upper edge136(FIG. 1) facing window232may have a calibration pattern. Accordingly, when an image is captured while the system is not in use, the image may contain the calibration pattern. By comparing a calibration image to the calibration pattern, distortions introduced by the optical system, imaging array or other components can be identified. Based on this comparison one or more calibration factors may be computed. These calibration factors may include pixel by pixel gain adjustments, spatial transformations or other factors that can be applied to an image to compensate for distortion.

In the embodiment illustrated, the calibration image is captured periodically to compensate for changes in the system over time. However, to save power, the calibration factors are not computed until an image is to be captured. In other embodiments these functions may be performed at other times.

At block1432, an image is captured. Processing at block1432may include reading the output of an imaging array. Capturing an image at block1432may also include applying the calibration factors computed to block1430.

Once the image is captured, the image may be processed to identify denomination of the bill placed in the imaging area. An example of processing that may be used to identify a denomination at block1434is provided in conjunction withFIG. 15below. Though, any suitable processing may be performed.

Regardless of the specific processing used to identify the denomination, once the denomination is identified, processing proceeds to block1436where the denomination is announced. The mechanism of announcing the denomination at block1436may depend on the mode set based on processing at block1424. In scenarios in which the mode has been set at block1424for an audible output, the denomination may be announced by a series of tones. Though, in some embodiments, the denomination may be announced using synthesized speech or other audible identification of the denomination. In embodiments in which the mode has been set for a tactile output, the denomination may be announced as a series of vibration pulses.

Regardless of how the denomination is announced, once the denomination has been announced, processing may proceed to block1438. At block1438user preferences, such as the volume and mode of output determined at block1424may be stored. Additionally, other data, such as the calibration parameters determined at block1430may be stored. This information may be stored in non-volatile memory such that it will be retained when the system is powered off. Thereafter, the system may be fully or partially powered off to conserve power until user input again indicating that a bill is to be read is received. If active components are used to monitor for a button press or to periodically “wake up” the system to capture a calibration image, those components may stay powered on, for example, but all other components may be powered off.

FIG. 15illustrates an exemplary process that may be performed to identify a denomination of a bill of currency at block1434. That processing begins at block1510where a portion of the captured image containing a printed area of the bill is identified. Such an identification may be made in any suitable way. An example of processing to identify the printed area is provided in conjunction withFIG. 16below.

Regardless of how the printed area is identified, processing proceeds to block1520where the image contained within the printed area is recognized. In embodiments in which the assisted reading device is a currency reader, recognizing an image in the printed area involves recognizing the denomination of the bill.

In the embodiment illustrated, denomination of a bill is recognized using a fast normalized cross-correlation function (FNCC). The FNCC process involves comparing templates representing features of denominations of currency to the identified printed area of the bill of currency. The denomination associated with the template that best matches the identified print area is selected as the denomination of the bill of currency.

In the FNCC process, a score is computed for each template, representing a degree of correlation between the template and the identified printed area. These scores can then be compared to select the template that best matches the printed area. Alternatively or additionally, other processing is possible based on the scores. For example, if the highest score is below some threshold value, indicating a relatively poor correlation between the template and the image, the user may be signaled because a low score could indicate that the object in the imaging area is not a bill of currency or, due to an error or other factors, an accurate image of the object was not acquired.

The templates representing denominations may be acquired in any suitable fashion. For example, the templates may be derived from images of samples of bills of currency of known denomination. Features of the bills that are useful in distinguishing between bills of different denominations may be recognized using manual or automated processing. The templates may be created by emphasizing the distinguishing features.

In some embodiments, the templates are represented as an array of pixel values. The template array may have fewer pixels than the identified print area. In such embodiments, the FNCC process may entail a comparison of the template to multiple sub-regions of the identified printed area to find the sub-region at which the template best matches the acquired image. The correlation between this sub-region and the template is taken as the score for the template.

According to the FNCC process, the sub-region of the printed area best matching a template is identified in a two phase process. During the first phase, the template is sequentially compared to only a portion of the possible sub-regions throughout the identified print area. From these sub-regions, the sub-region that best matches the template is selected. In the second phase, sub-regions surrounding this selected sub-region are compared to the template.

As part of the comparison of the template to a sub-region, scores representing the correlation between the template and each of the sub-regions is computed. The highest score computed for any of the sub-regions during the second phase is selected as the overall score for the comparison of the template to the identified print area. In this way, the template is not compared to every possible sub-region of the identified printed area. Because multiple templates are compared to the identified print area in order to recognize the denomination of a bill of currency, limiting the number of comparisons required can speed identification of the denomination. Though, it should be appreciated any suitable processing may be used to recognize a denomination.

Regardless of the manner in which the denomination is identified, a token or other indication of the recognized denomination is returned at block1530. In the embodiment illustrated, the processing inFIG. 15is implemented as a sub-program called by the program implementing the processing ofFIG. 14. Accordingly, the token, once returned, may be used for processing at block1436(FIG. 14) to announce the recognized denomination or for other reasons. Regardless of the manner in which the recognized denomination is used, the processing ofFIG. 15ends after the token identifying the denomination is generated.

Turning toFIG. 16, an example of a process to identify the portion of an image representing a printed area is provided. In the embodiment illustrated, portions of an acquired image that depict borders on the bill of currency are first identified. Any portions of the image inside the border are deemed to be printed areas of the bill of currency. Though any suitable method may be used to identify borders, a histogramming approach may be used in some embodiments.

FIG. 16illustrates an example of such a process. The process ofFIG. 16begins at block1610where the portions of the image expected to contain non-printed borders are selected for processing. In embodiments illustrated above, a bill of currency may be recognized from an image of a corner of the bill and position sensors are used to control image acquisition such that an image is acquired when the corner of the bill is aligned in an imaging area. Accordingly, the acquired image can be expected to contain sides of the bill of currency along two predefined sides of the imaged area. The non-printed border can therefore be expected to be adjacent to these sides. The pixels representing regions adjacent these sides may be selected at block1610for processing.

The selected portions of the image may be filtered or otherwise processed to highlight differences between non-printed border regions and other portions of the image. For example, processing at block1612may involve computing a Gaussian filter parameter, sigma, as is known in the art. The computed parameter may be applied at block1614to perform smoothing of the portion of the image selected at block1612using a Gaussian filter with the parameters determined at block1612.

The smoothed image may be further processed. For example, processing may be performed to enhance the appearance of edges of objects in the image. Accordingly, the exemplary process ofFIG. 16continues to block1616where X and Y differential operators are applied. At block1618, non-maximum suppression is performed using known techniques. Such processing has the effect of de-emphasizing portions of the image that are not indicative of edges of objects captured in the image. At block1620, a hysteresis threshold may be applied and an edge map may be created at block1622using known processing techniques. The edge map may represent the portion of the image selected at block1610with edges of objects emphasized.

Regardless of the preprocessing performed, a histogramming technique may be applied to rapidly identify a boundary between the portions of the bill of currency to be identified. The histogramming process may be performed twice, once along each side of the image such that both borders may be identified. At block1624processing is performed along one side and at block1626the same process is repeated along the perpendicular side.FIG. 17provides an example of the histogramming process that may be applied to detect the border along each side.

The process atFIG. 17begins at block1710where an array of memory locations representing a histogram is initialized. In this example, the array is initialized with zero values. At block1712, the histogram array is filled with values derived from the edge map created at block1622(FIG. 16). In this example, the array is filled with a value for each row or column of pixels parallel to the side of the bill along which a border region is to be detected. The value is derived by counting the number of non-zero points in the edge map computed at block1622. Consequently, the histogram array populated at block1712contains, in each successive entry, a count of the number of edge pixels that appear in the line parallel to the side of the bill along which the non-printed border region is to be detected. Each successive value in the array provides that count for a line one pixel width further away from the side of the bill. If the line passes through the non-printed border region, there should be few or no edges along that line and the count in the histogram array should be near zero. Accordingly, the values in the histogram array may indicate the location relative to the side of the bill of currency of the transition between a non-printed border area and the image area.

This processing begins at block1714where a detected flag is reset. At block1716, processing of the histogram array begins, starting with the value representing the line closest to the side of the bill.

At decision block1720, the process branches depending on whether all values in the array have been checked. If all entries have not been checked, processing branches to block1722. Conversely, if all entries have been checked, processing branches to block1736.

At block1722the histogram value at the next location in the array is checked. If the edge detected flag is set, processing branches to block1736. Conversely, if the edge detected flag is not set, processing continues to decision block1726.

At decision block1726, the process branches depending on whether the histogram value being checked is above a threshold value. If not, the process loops back to decision block1720and1722where the next subsequent value in the histogram array is processed.

Conversely, if, as a result of the comparison at decision block1726, it is determined that the value in the histogram array exceeds the threshold, processing proceeds to block1728. If processing reaches block1728, the array value being processed may be tentatively assumed to define the transition between the non-printed border region and the print area of the image. In subsequent processing steps, this assumption may be verified.

At block1730, values from the initial image acquired of the bill of currency are processed. Pixels at the location identified at block1728, the presumptive boundary between the non-printed and printed areas of the bill, are selected for processing. An average intensity of pixels on each side of the presumptive boundary between printed and non-printed areas are computed. Processing branches at decision block1732depending on the magnitude of the difference between these intensity values. If the intensity difference is greater than zero, processing branches to block1734where the detected flag is set. Conversely, if the difference is not greater than zero, processing loops back to decision block1720, where the process may be repeated using a next value in the histogram array.

Following setting of the detected flag at block1734, processing proceeds to block1736. Processing may also arrive at block1736once all values in the histogram array have been checked, as determined at decision block1720.

Regardless of how processing reaches block1736, an average pixel intensity value is computed for a long narrow strip of pixels within the region presumed to be a portion of the non-printed border region based on the location presumptively set at block1728. In the example illustrated, the long narrow strip of pixels is 10 pixels long by two pixels wide. However, any suitable sized region may be used for the calculation.

The process branches at decision block1740, depending on the value of the average intensity computed at block1736. If the average is less than a threshold, for example150, the location determined at block1728may be regarded as confirmed, and the processing ofFIG. 17may end with a value computed at block1728as the confirmed location of the boundary between the printed and non-printed areas of the bill of currency. Conversely, if the average is not less than the threshold applied at decision block1740, the process may continue to decision block1742. At decision block1742, the process may again branch. At decision block1742, the process branches, depending on the values of the pixels in the long narrow region selected at block1736. If the values of the pixels over that region differ by more than a threshold, the process may branch to block1744. If processing reaches block1744, it may be assumed that pixels falling within the non-printed border region identified at block1728are actually within a printed area of the bill and the border region is set to zero. Setting a border region to zero may increase the amount of processing required at block1520(FIG. 15) when correlating templates to the recognized printed area. However, it increases the accuracy of the recognition performed at block1520by ensuring that regions of the printed area are not unintentionally discarded by incorrectly labeling those regions as part of the non-printed border area.

Once the processing of block1744is completed, the process of identifying a non-printed border area may be completed. Similarly, if, as determined at decision block1742, the pixel intensity difference is not less than the threshold, the processing similarly ends. If processing ends following decision block1742because the pixel intensity difference is not less than the threshold, the edge of the non-printed border region will be as determined at block1728.

As one example, output devices such as a speaker and a mechanical vibrator are described. Other output devices may alternatively or additionally be used and the device need not be integral with the assistive reading device. For example, a wireless connection may be provided to a headset, such as a Bluetooth headset, may be included as an output device.