Abstract:
An image capture device, methods and system for reducing blurring or streaking of a captured image induced by the movement of an object past the image capture device. During the image capture cycle, intermediate light values in each pixels within the image capture device are transferred to an adjacent pixels allowing the integration of the light values to follow the movement of the object being captured.

Description:
TECHNICAL FIELD  
       [0001]    The invention described herein relates generally to improvements to semiconductor based image capture devices. More particularly, the invention relates to improving the quality of an image by reducing motion blur associated with the movement of an object whose image is being captured by an image capture device. 
       BACKGROUND  
       [0002]    Bar code scanners are used in a wide variety of applications that rely on information stored in bar codes. Industries such as retail, airline, self-service, automotive, parcel delivery, pharmaceutical, healthcare and others use bar codes to provide inventory control, customer identification, item tracking, security and many other functions. A typical bar code is comprised of a number of bars separated by spaces. Information is encoded on a bar code by varying the width of the bars and spaces. When a bar code is placed within the field of view of a bar code scanner, the scanner will detect, analyze and decode the bars and spaces comprising the bar code to retrieve the information encoded wherein. This operation is also called scanning or reading a bar code. The information encoded on a bar code is usually a sequence of numeric or alphanumeric symbols (e.g., a Universal Product Code (UPC) or European Article Number (EAN)). 
         [0003]    An imaging bar code scanner (also referred to as an image scanner) reads a bar code by capturing a digital image of the bar code and then processing the image to detect and decode the bar code. It is advantageous for the bar code scanner to successfully read all bar codes presented to the scanner on the first pass of each bar code by the scanner. This is known as a successful first pass read. Successful first pass reads of bar codes helps to maintain a good workflow at the checkout station and speeds up the overall checkout process. A high success rate for first pass reads has also been found to reduce stress on the person operating the scanner. This is particularly true if the operator is a customer operating a self-checkout terminal. 
         [0004]    High performance passby barcode scanners based upon image capture and image processing technology have been slow to be adopted in passby scanning environments. In a retail environment, an image scanner must achieve an object passby speed of  30  to  50  inches per second. The image scanners on the market today have not proved capable of such speeds, which is one reason why laser based barcode scanners dominate the passby scanning environments. 
         [0005]    One important barrier that has prevented image scanners from reaching such high passby speeds is the poor image quality of a bar code when the bar code is moving past the image scanner at high speeds. The poor quality can be attributed in part to motion blur. Motion blur occurs when an image of an object moves across multiple pixels of an image capture device during the period of time the image is being captured. The result is a captured image where the object in motion is blurred or has streaks thus making it difficult or in some cases impossible to properly identify the object in the captured image. 
         [0006]    Therefore, it would be desirable to provide an image capture device that does not suffer from above deficiencies. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0007]    The invention, in accordance with preferred and exemplary embodiments, together with further objects and advantages thereof, is more particularly described in the following description taken in conjunction with the accompanying drawings in which like reference characters designate the same or similar parts throughout the several views and wherein: 
           [0008]      FIG. 1  is a high level block diagram illustrative of an embodiment of an image scanning system; 
           [0009]      FIG. 2  is a high level block diagram illustrative of an embodiment of a semiconductor image capture device; 
           [0010]      FIG. 3A  is a high level cross section diagram illustrative of a reversed biased photodiode; 
           [0011]      FIG. 3B  is a high level architectural schematic of a four transistor ( 4 T) pixel (prior art); 
           [0012]      FIG. 4A ,  4 B and  4 C are high level diagrams depicting, at different points in time, the image of a bar code segment positioned over a group of pixels; 
           [0013]      FIG. 5  is a high level architectural schematic of a four transistor pixel ( 4 T) with a pixel to pixel charge transfer feature; 
           [0014]      FIG. 6A ,  6 B and  6 C are high level diagrams depicting, at different points in time, the image of a bar code segment positioned over a group of pixels where each pixel has a pixel to pixel charge transfer feature; and 
           [0015]      FIG. 7  is a high level flow diagram illustrating the transfer of a partially integrated charge value from one pixel to an adjacent pixel. 
       
    
    
     DETAILED DESCRIPTION  
       [0016]    In the following description, numerous details are set forth to provide an understanding of the claimed invention. However, it will be understood by those skilled in the art that the claimed invention may be practiced without these details and that numerous variations or modifications from the described embodiments are possible. 
         [0017]    With reference to  FIG. 1 , there is provided a high level illustration, in block form, of an embodiment of an image scanning system  100 , which is used to scan a bar code  145 . The image scanning system  100  comprises an image scanner  115 , a store server  155  and a bar code  145  printed on a label  150 . The image scanner  115  communicates with the store server  155  over a computer data network  160 . The network  160  can be a wired network (e.g., an Ethernet network) or wireless network (e.g., an IEEE 802.11G based network) or a combination of both. In some embodiments, the store server  155  is physically removed from the store where the image scanner  115  is located and communicates with the image scanner  115  over the Internet or a wide area network or a combination of these or different types of networks. In some embodiments, multiple image scanners  115  communicate over the data network  160  to the store server  155 . 
         [0018]    The image scanner  115  includes an image-focusing device  125  that receives an image and focuses the image onto an image capture device  120 . The image scanner  115  is further comprised of a processing module  130 , user interface hardware  140 , and communications hardware  135 . The processing module  130  comprises at least one processor, memory, stored instructions and control and interface hardware to control the other devices and modules of the image scanner  115 . The processing module  130 , by executing the stored instructions, controls the hardware devices and modules that comprise the image scanner  115  or are connected to the image scanner  115 . In addition, the stored instructions cause the processor to: process data such as an image that is captured by the image capture device  120 , control the communications hardware  135  to implement protocols used on the data network  160  and implement other software features and functions of the image scanner  115 . In some embodiments, the store server  155  sends the image scanner  115  updates to the stored instructions or to the operating parameters of the image scanner  115 . These updated stored instructions are stored in the image scanner  115  and then executed as required. 
         [0019]    Image capture device  120  converts light reflected from bar code  145  into electrical signals. The source of the reflected light may be ambient light or light from an illumination device if sufficient ambient light is unavailable. The image capture device  120  is a silicon-based device with both optical and integrated circuits and may be fabricated as a complimentary metal oxide semiconductor (CMOS) integrated circuit. Image capture device  120  may include a charge coupled device (CCD) or a CMOS device. 
         [0020]    Image capture device  120  captures an optical image, focused on its surface, by converting the optical image to an electronic digital image comprising pixel information organized into rows and columns. The time required to read all of the raw pixel data from the image capture device  120  is relatively long compared to the time required to simply capture the digital image in the image capture device  120 . 
         [0021]    Turning to  FIG. 2 , there is provided a high level block diagram of an image capture device  120 . In this embodiment, the image capture device  120  is implemented as a CMOS device. The pixel array  205  defines the optically active area of the image capture device  120  and is where light or photon energy is converted into electric energy and stored as individual pixel data. An individual pixel contains data wherein the magnitude of the data is proportional to the total amount of photon energy striking a given area of the pixel array  205  integrated over a period of time. The pixels are physically organized into rows and columns. Timing and control logic  265  controls the operations of the image capture device  120  including capturing an image and reading pixel data from the pixel array  205  that represent the captured image. External interface  260  provides access to and control of the timing and control logic  265  to external devices (i.e., a processor  130  or specialized hardware designed or programmed to process data from the image capture device  120 ). The external interface  260  is also used to receive commands from the external device and to send and receive data, including pixel data. Pixel data, captured by the image capture device  120 , is transferred from the pixel array  205  to a pixel buffer  255  and then transferred externally through the external interface  260  when an external device signals it is ready to except the data. The timing and control logic  265  controls the operation of the pixel buffer and movement of pixel data through an internal interface  270 . The external interface  260  interfaces with a data/control bus (not shown) that is external to the image capture device  120 . The timing and control logic  265  manages the interaction with the data/control bus and the external device or devices. 
         [0022]    One approach to read pixel data from the image capture device  120  is to issue a read-out all pixel data command. This command causes the timing and control logic  265  to load the row latches  215  with the first row number of the pixel array  205  and the column latches  235  with the first column number of the pixel array  205 . The row latches  215  drive a row counter  220  which increments the row number on command from the timing and control logic  265  to allow each row of the pixel array to be selected in its turn or as needed. The output of the row counter  220  drives a row decoder  225 , which generates a select row signal corresponding to a single row in the pixel array  205 . The output of the row decoder  225  connects to the row drivers  230 , which buffers and transmits a row select signal  380  to the pixel array  205  to select a single row of pixel data. The column latches  235  drive a column counter  240 , which will increment the column number on command from the timing and control logic  265  to allow each column in a row to be selected in its turn or as needed. The output of the column counter  240  drives a column decoder  245 , which generates a single column select signal  375  corresponding to a single column in the pixel array  205 . The output of the column decoder  245  connects to the column drivers  250 , which buffers and transmits a column select signal to the pixel array  205 . The row and column select signals  380 ,  275  combine to select a single pixel from the pixel array  205 . The pixel data for the selected pixel is moved to the pixel buffer  255  where it is stored before being read by a processor module  130  or a computer or computer logic that is external to the image capture device  120 . In some embodiments, the pixel buffer  255  buffers data from multiple pixels so that multiple pixels are read with each external access to the image capture device. This reduces the bus time needed to read the entire pixel array  205 . In some embodiments, the pixel buffer  255  conditions or transforms the pixel data from an analog form to a digital form. 
         [0023]    With reference to  FIG. 3A , there is provided a high-level cross section diagram illustrative of a reversed biased PN junction photodiode  300 . The photodiode  300  is configured to be a charge collection device where the charge on the photodiode  300  is proportional to the number of photons that strike the photodiode  300 . The diagram depicts a portion of a silicon substrate containing photodiode  300 , which is part of an array of photodiodes. Each photodiode, along with some additional circuitry, is defined as a pixel. When used as a charge collection device, the photodiode  300  is configured to operate in the reversed biased mode. In this mode of operation, the p region  330  of the photodiode is connected to ground while the n +  region  320  is connected to transistor M RST    310 . A depletion region  325  separates the p region  330  from the n+ region  320  on the silicon substrate. Prior to starting the process of capturing photons, the n +  region  320  is charged or reset to a positive voltage V RST    315  by RESET signal  305 , which turns on transistor M RST    310 . Removing the RESET signal  305  turns off transistor M RST    310  which initiates the photon collection period. With the photodiode  300  held in a reverse bias condition, the n +  region  320  is electrically floating at the initial positive voltage of V RST    315 . Electrons excited by photons  335  striking the photodiode  300  collect in the n +  region  320 , reducing the initial voltage placed on this region; holes flow to the ground terminal attached to the p region  330 . At some point, the photon collection period ends and the value of the remaining or final voltage in the n +  region  320  is read. The value of the final voltage is proportional to the number of photons that impinged on the photodiode  300  during the photon collection period. A final voltage that is near the initial V RST  voltage  315  correlates to receiving few photons or having the photodiode  300  exposed to a very low light. A final voltage that is near zero volts correlates to receiving a larger number of photons or having the photodiode  300  exposed to an intense light. The more photons that impinge on the photodiode  300 , the more the initial reset voltage V RST    315  is reduced. 
         [0024]    This embodiment uses a photosensitive device, which in this case is a PN junction photodiode  300 . In other embodiment, different photosensitive devices can be used, such as a photodiode with a PIN structure or a phototransistor. 
         [0025]    Turning to  FIG. 3B , there is provided a high level architectural schematic of a four transistor (4T) pixel. In this embodiment, a photosensitive device  300  and four transistors are used to implement each pixel. The p region  330  of the photodiode  300  is connected to ground and the n +  region  320  is connected to transistors M RST    310  and M SAM    345 . Prior to starting the photon collection period (also known as capturing a pixel or image), RESET signal  305  is activated causing transistor M RST    310  to turn on which charges the n +  region  320  of the photodiode  300  to voltage V RST    315 . The V RST    315  voltage is the starting or reference voltage for the photodiode  300 . The photon collection period ends when SAMPLE signal  340  activates causing transistor M SAM    345  to capture the instantaneous voltage on the n +  region  320  of the photodiode  300 . This is the final voltage and it is less than or equal to the reference voltage. Using the M SAM    345  transistor in this manner creates an electronic snapshot shutter. The SAMPLE signal  340  is connected to all pixels in the pixel array  205 . Therefore, when the SAMPLE signal  340  is activated, all pixels in the pixel array  205  capture the final voltage their respected pixel. The output of transistor M SAM    345  is sent to buffer transistor M BUF    355 . Transistor M SEL    360  is used to select the output of the pixel for reading. A ROW SELECT signal  380  is placed on the gate of transistor M SEL    360  and a COLUMN SELECT signal  375  is placed on the drain of the transistor. The output (final voltage) is transferred to the pixel buffer  255  ( FIG. 2 ), which generates and stores a digital value based on the difference between the starting voltage and the final voltage of the pixel cell. In some embodiments, the starting voltage can be outputted by selecting the output of the pixel prior to starting the photon collection period but after the photodiode  300  has been reset. 
         [0026]    In other embodiments, a five or more transistor configuration is used to form the basic circuitry of a pixel. These embodiments may implement additional features for each pixel but their configurations will still work with the present invention. 
         [0027]    Moving to  FIG. 4 , there are provided three subfigures ( 4 A,  4 B and  4 C) each depicting, at a different point in time, the image of a bar code segment  400  moving from left to right  420  across five pixels  425  that are a part of a row of pixels in the pixel array  205 . The movement of the bar code segment  400 , as depicted in the three figures, occurs during a single photon collection period, which simulates what happens when a bar code is moved passed an image scanner at high passby speeds. The number within each pixel ( 430 - 434 ) and shown on each subfigure represents the percent reduction in voltage from the reference voltage  315  for that pixel caused by photons that have impinged on the photodiode of the pixel, up to the point in time represented by the subfigure. The photon collection period is divided into three equal time periods.  FIG. 4A  represents the conditions of the photodiodes after one-third of the photon collection period has passed.  FIG. 4B  represents the conditions of the photodiodes after two thirds of the time period has passed and  FIG. 4C  represents the conditions of the photodiodes at the end of the photon collection period. 
         [0028]    With reference to  FIG. 4A , the photon collection period starts with the image of the bar code segment  400  in this position. (Note: dark areas of the bar code segment represent no or low levels of photons and white areas represent high levels of photons.) Three dark areas  413 ,  415 ,  416  are positioned over the second, forth and fifth pixels  431 ,  433 ,  434 . The photodiodes in these three pixels sustain no or minimal reduction in voltage because few photons impinge them. Two white areas  412 ,  414  are positioned over the first and third pixels  430 ,  432 . The photodiodes in these two pixels receive photons and have their voltage reduced to 80% of the reference voltage. 
         [0029]    Turning to  FIG. 4B , the photon collection period continues and the image of the bar code segment  400  moves to a new position, as shown. Three dark areas  411 ,  413 ,  415  are now positioned over the first, third and fifth pixels  430 ,  432 ,  434 . The voltage on the photodiodes of these pixels remains unchanged because few if any photons are impinging on the photodiode of each pixel. Two white areas  412 ,  414  are now positioned over the second and forth pixels  431 ,  433 . The voltage on the photodiodes of these pixels where previously at 100% but now are reduced to 80% of the reference voltage due to the photons that have impinged on them. 
         [0030]    Turning to  FIG. 4C , the photon collection period continues and the image of the bar code segment has moved to a new position, as shown. Three dark areas  410 ,  411 ,  413  are now positioned over the first, second and forth pixels  430 ,  431 ,  433 . The voltage on the photodiodes of these pixels remains unchanged because few if any photons are impinging them. Two white areas  412 ,  414  are now positioned over the third and fifth pixels  432 ,  434 . The voltage on the photodiodes of these pixels where previously at 80% and 100% of the reference voltage respectively, but now are reduced to 60% and 80% respectively due to the photons that impinged on them. 
         [0031]    The photon collection period ends with the image of the bar code segment in the position depicted in  FIG. 4C . The first, second, forth and fifth pixels  430 ,  431 ,  433 ,  434  all have final photodiode voltages that are 80% of the reference voltage which represents a dark area. The letter “D” appears in each of these pixels. The third pixel  432  has a final photodiode voltage that is 60% of the reference voltage, which represents a white area. The letter “W” appears in this pixel. The five pixels  430 ,  431 ,  432 ,  433 ,  434  have the following final values when the voltages are converted to either dark or white space values: “DDWDD.” However, the segment  400  of the bar code being presented to the pixels has the value “DDWDWDD.” The five pixels  430 ,  431 ,  432 ,  433 ,  434  have failed to properly capture the segment  400  of the bar code that was presented. The failure to properly read a segment of the bar code leads to a failure to read the entire bar code requiring the bar code to be presented a second or more times for reading. This points out the deficiency of the prior art pixel circuitry as shown in  FIG. 3A  and  FIG. 3B . 
         [0032]    With reference to  FIG. 5 , there is provided a high level architectural schematic of a new pixel  500  design that uses a basic four transistor (4T) design with a pixel-to-pixel charge transfer feature. The charge transfer feature allows the instantaneous charge or voltage on a photodiode  300  of one pixel to be transferred to a photodiode  300  in a neighboring pixel. The charge transfer operation can be carried out one or more times during the photon collection period. Using this feature, as an image of an object moves across the pixel array  205 , the charge integrated in each pixel associated with each segment of the image can be moved from pixel to pixel to follow the image as it moves across the pixel array  205 . This causes the capture of a more accurate representation of the image and avoids the error shown in  FIGS. 4A ,  4 B, and  4 C. 
         [0033]    Continuing with  FIG. 5 , transistors M TRF1    505 , M TRF2    515  and resistor  520  are added to the 4T pixel circuits to create and buffer transfer voltage V TFR(P)    510 . Transfer voltage V TFR(P)    510  is equal to the instantaneous voltage on the photodiode  300 , at the time it is sampled. The source connection on transistor M TRF2    515  is connected to ground  535  through resistor  520 . This provides a path to ground to drain charge from neighboring photodiode if that is required for the neighboring photodiode to reach the proper voltage. The subscript “P” represents the relative location of the pixel in a row of pixels. The pixel to the left would be “P−1” (not shown). The pixel to the right would be “P+1” (not shown). 
         [0034]    The process of transferring the instantaneous voltage of the photodiode in pixel “p” to the photodiode in pixel “P+1” starts by capturing the instantaneous voltage of the photodiode  300  in pixel “P”. A snapshot of the voltage on the photodiode  300  is taken by activating and removing signal SAMPLE  340 . Next, the TFR_CMD signal  525  is activated, which turns on transistors M TRF1    505  and M TRF2    515  creating and driving voltage V TFR(P)    510 . V TFR(P)    510  is connected to the photodiode of its neighbor pixel “P+1” (not shown however the connection to pixel “P+1” is identical the element  530  of pixel “P” which connects pixel “P−1” to “P”) which receives the voltage signal. The received signal is then used to set the charge (voltage potential) on the photodiode of pixel “P+1”. The charge on the photodiode moves up or down until it reaches the voltage V TFR(P)    510 . When the TFR_CMD signal  525  is removed, the photodiode of pixel “P+1” continues to capture photons until the photo collection or integration period ends. The SAMPLE signal  340  and the TFR_CMD signal  525  are common to all pixels. The transfer of a photodiode voltage from one pixel to an adjacent pixel is referred to as a photodiode voltage transfer cycle. During each photodiode voltage transfer cycle, all pixels of the pixel array  205  are involved in the transfer. For example, as the voltage of pixel “P” is transferred to pixel “P+1,” the voltage of pixel “P−1” is being transferred to “P”. 
         [0035]    In this embodiment, the charge transfer occurs from left to right in a row of pixels. So the instantaneous photodiode voltage of pixel “P−1” is transferred to photodiode  300  of pixel “P” as voltage V TFR(P−1)    530 . The instantaneous photodiode  300  voltage V TFR(P)    510  of pixel “P” is transferred to the photodiode of pixel “P+1”. Thus, the instantaneous photodiode voltage of each pixel in a row is simultaneously transferred to the photodiode of the adjacent pixel located to its right. The instantaneous photodiode voltage is likewise simultaneously transferred for all pixels in all rows of the pixel array  205 . The first pixel of each row has no pixel to it&#39;s left; therefore the voltage of each of these pixels is set to the reference voltage during the transfer cycle. The last pixel in each row has no pixel located to its right so while the transfer voltage is created for output, there is no pixel to receive the voltage. 
         [0036]    In other embodiments, the instantaneous photodiode voltage transfer occurs from right to left on a row. In still other embodiments, the transfer is not between pixels on a row but between pixels in a column. The instantaneous photodiode voltage is transferred from a pixel in one row to a pixel in an adjacent row in the same column. In further embodiments, the image capture device can be programmed to transfer the instantaneous photodiode voltage from a pixel to any adjacent pixel in any direction. This allows for additional flexibility when trying compensating for the movement of objects that passby the image scanner. 
         [0037]    In the below example, three photodiode voltage transfer cycles occur during a single photon collection period. The number of transfer cycles per photon collection period is programmable and can be set to zero so that the photon collection period operates similar to conventional image capture devices. When a determination is made that objects are or will passby the image capture device  120  at high speeds, the number of transfer cycles per photon collection period is set to a high number to mitigate the high passby speed of the objects. A low number of transfer cycles per photon collection period can be used when objects move slowly pass the image capture device  120 . The Timing and Control Logic  265  controls the photodiode voltage transfer cycle and the photon collection period. 
         [0038]    With respect to  FIG. 6 , there are provided three subfigures ( 6 A,  6 B and  6 C) similar to the figures in  FIG. 4  except the pixels represented in the figures  FIG. 6  have the additional photodiode voltage transfer feature as depicted in  FIG. 5 . In this example, the image capture device  120  is programmed to have two photodiode voltage transfers cycles per photon collection period and the five pixels  625  transfer their photodiode voltage from left to right in the same row. The image of a bar code segment  400  is the same as in  FIG. 4  and moves from left to right  420  across the five pixels  625  that are a part of a row of pixels in a pixel array  205 . The movement of the bar code segment  400 , as depicted in the three figures, occurs during a single photon collection period, which simulates what happens when a bar code is moved passed an image scanner at high passby speeds. The number within each pixel ( 630 - 634 ) shown on each subfigure represents the percent reduction in photodiode voltage, from the reference voltage  315  for that pixel, caused by photons that have impinged on the photodiode of the pixel up to the point in time represented by the figure. The photon collection period is divided into three equal time periods.  FIG. 6A  represents the conditions on the photodiode after one-third of the photon collection period.  FIG. 6B  represents the conditions on the photodiode after two thirds of the time period and  FIG. 6C  represents the conditions on the photodiode at the end of the photon collection period. A photodiode voltage transfer cycle occurs after the one-third and two-thirds points in the photon collection period. The values shown in  FIG. 6A and 6B  are the photodiode values just prior to the transfer cycle and represent the photodiode values transferred to the next pixel. 
         [0039]    With reference to  FIG. 6A , the photon collection period starts with the image of the bar code segment in this position. (Note: dark areas of the bar code segment represent no or low levels of photons and white areas represent high levels of photons.) Three dark areas  413 ,  415 ,  416  are positioned over the second, forth and fifth pixels  631 ,  633 ,  634 . The photodiodes of these three pixels sustain no or minimal reduction in voltage because few photons impinge on them. Two white areas  412 ,  414  are positioned over the first and third pixels  630 , 632 . The photodiodes of these two pixels receive photons and have their photodiode voltage reduced to 80% of the reference voltage. 
         [0040]    After the snapshot of  FIG. 6A  and before the start of the second portion of the photon collection period, a photodiode voltage transfer cycle occurs and the instantaneous voltage on each photodiode of each pixel is transferred or shifted to the photodiode of the pixel to the right on the same row. Once the voltage has been transferred, the photon collection continues until the two-thirds point in the photon collection period is reached. The image of the bar code segment moves to a new position. The image position and the values of the photodiodes of the pixels at this point in time are shown in  FIG. 6B . The photodiode voltage of each pixel has been shifted to the right by one and the photodiode voltage of the first pixel was reset to the reference voltage  315 . Three dark areas  411 ,  413 ,  415  are now positioned over the first, third and fifth pixels  630 ,  632 ,  634 . The photodiode voltage of these pixels remains little changed because few if any photons have impinged on these pixels during this period or on the prior pixels during the first time period. Two white areas  412 ,  414  are now positioned over the second and forth pixels  631 ,  633 . After the voltage transfer cycle, the starting photodiode voltage of the second and forth pixels  631 ,  633  was set to 80% and during the second time portion of the photon collection period, the voltage on the two pixels was further reduced to 60% due to the photons that impinge on the photodiodes of these pixels. 
         [0041]    After the snapshot of  FIG. 6B  and before the start of the third and last portion of the photon collection period, a photodiode voltage transfer cycle occurs and the instantaneous voltage on each photodiode of each pixel is transferred or shifted to the photodiode of the pixel to the right. Once the transfer cycle is complete, the photon collection continues until the end of the collection period is reached. The image of the bar code segment also moves to a new position. The image position and the final photodiode voltage of the pixels at this point in time are shown in  FIG. 6C . At the start of the last part of the collection period, the value of each pixel was shifted to the right by one and the photodiode voltage of the first pixel was again reset to the reference voltage  315 . In  FIG. 6C , three dark areas  410 ,  411 ,  413  are now positioned over the first, second and forth pixels  630 ,  631 ,  633 . The photodiode voltage of these pixels remains unchanged because few if any photons have impinged on these pixels or on the prior pixels during either of the first two time periods. Two white areas  412 ,  414  are now positioned over the third and fifth pixels  632 ,  634 . The photodiode voltage of these pixels after the second voltage transfer cycle was set to 60% and have been further reduced to 40% due to the photons that impinged on the photodiodes of each pixel during the last portion of the photon collection period. 
         [0042]    The photon collection period ends with the photodiode values and the image of the bar code segment in the position depicted in  FIG. 6C . The first, second and forth pixels  630 ,  631 ,  633  all have final photodiode voltages that are 100% of the reference voltage which represents a dark area. The letter “D” appears in each of these pixels. The third and fifth pixels  632 ,  634  have a final photodiode voltage that is 40% of the reference voltage, which represents a white area. The letter “W” appears in each pixel. The five pixels  630 ,  631 ,  632 ,  633 ,  634  have the following final values when converted to either dark or white space values: “DDWDW.” This matches the last five segments of the bar code image that was moved across the pixels, which are “DDWDW”. This would result in a correct read of the bar code. Without the voltage transfer cycles, the image capture device failed to properly read the bar code as illustrated in  FIG. 4 . In addition to properly reading the bar code, the contrast ratio was also improved. In this example, the dark value was at or near 100% of the reference voltage  315  and the white value was at or near 40% of the reference voltage. This method created a difference of 60% of the reference voltage between white and dark areas. In the previous example where no voltage transfer was performed, the dark value was 80% of the reference voltage  315  and the white value was 60% of the reference voltage. This method created a difference of only 20% of the reference voltage  315  making it harder to distinguish between the dark and light areas thus lowering the probability of properly reading the bar code. 
         [0043]      FIG. 7  is a high level flow diagram illustrating the movement of a partially integrated charge or voltage value from one pixel to an adjacent pixel where the integration of the charge continues based on the number of photons received. The process is called the photodiode voltage transfer cycle or transfer cycle for short. This process occurs simultaneously in all pixels within the pixel array  205  so that the instantaneous charge value of each pixel is shifted to an adjacent pixel at the same time through out the pixel array  205 . This diagram shows what happens within pixel “P” and how pixel “P” interacts with adjacent pixels. A similar process occurs in every pixel during the transfer cycle. 
         [0044]    Prior to the beginning of the photon collection period (also known as the charge integration period), the charge on the photodiode  300  is reset to a reference voltage  315  by the application of RESET signal  305 (step  700 ). When the RESET signal  305  is removed, the charge on the photodiode  300  floats because the PN junction of the photodiode  300  is reversed biased. The photon collection period starts once the charge on the photodiode  300  is allowed to float (step  710 ). At some point during the photon collection period, the SAMPLE  340  and TFR_CMD  525  signals are asserted to all pixels in the pixel array  205  (step  720 ). The instantaneous charge on the photodiode  300  of pixel “P” is captured as a voltage V TFR(P)    510  when the SAMPLE  340  signal is asserted and removed. This represents the integration of charge from photons that have impinged on the photodiode  300  from the start of the photon collection period to this point in the collection period. A signal with voltage V TFR(P)    510  is then driven externally to adjacent pixel “P+1” when the TFR_CMD  525  signal is asserted (step  730 ). Pixel “P+1” receives the signal and charges its photodiode to voltage V TFR(P)    510 . At the same time, pixel “P” receives a signal V TFR(P−1)    530  from pixel “P−1” that represents the charge on the photodiode of pixel “P−1”. Pixel “P” takes the received signal and charges its photodiode  300  to voltage V TFR(P−1)    530  (step  740 ). Signal TFR_CMD  525  is removed from all pixels in the pixel array  205  and the photon collection period continues (step  750 ). At some point in time, the TFR_CMD  525  signal is asserted to all pixels in the pixel array  205 . This causes the photon collection period to end for all pixels and captures the final voltage on the photodiode of each pixel (step  760 ). The final voltage is then driving out of pixel “P” as voltage Vout when the ROW SELECT  380  and COLUMN SELECT  375  signals are asserted for pixel “P” ( 770 ). 
         [0045]    While the invention is disclosed in the context of an image capture device used to read optical codes, it will be recognized that a wide variety of implementations may be employed by a person of ordinary skill in the art consistent with the above discussion and the claims, which follow below. In addition, the image capture device  120  can be used in other functions not associated with bar code recognition.