Abstract:
A hand-held imager which is capable of reading both linear and two dimensional symbologies, which can perform focusing and illuminating steps quickly and accurately so as to eliminate variation in the position of the imager relative to the code becoming a negative factor, in which can operate in an environment where the imager is anywhere from 1.5 inches to 16 inches from the code. The imager includes an imaging system having a focusing system, an illumination system, and a two-dimensional photodetector which forms an image of the coded symbology. After achieving targeting of the coded symbology, the scanning system adjusts the focus between multiple different focuses, and utilizes a portion of the two-dimensional photodetector to determine the optimum focus. Upon the determination of optimum focus, the focusing system is returned to the focusing configuration established in the initial focusing step, and an image is created using the entire two-dimensional photodetector. Optimum illumination is determined using the same two-dimensional photodetector.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application is a divisional of U.S. patent application Ser. No. 09/151,764, filed Sep. 11, 1998. This application is related to co-pending U.S. patent application Ser. No. 09/151,766 (Symbology Imager Systems and Reading Apparatus and Method) and U.S. patent application Ser. No. 09/151,765 (Diffused Surface Illumination Apparatus and Method) the entire disclosures of which are incorporated herein by reference. Further, International application Ser. No. WO97/42756 filed on May 6, 1966, for a Smart Progressive-Scan Charge Coupled Device Camera, and which was filed by CIMatrix, one of the co-applicant&#39;s of the present application is also incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to an imager for reading optical symbologies such as traditional bar codes and 2D symbologies. More particularly, the present invention relates to a hand-held optical code imager which quickly and easily adjusts illumination and focus and has a preferred operating range of approximately 1.5 to 16 inches, however, the imager may have an operating range with both lower and higher limits, and still fall within the intended scope of the present application.  
         [0004]     2. Description of the Prior Art  
         [0005]     The use of bar codes has proliferated to the point where they are used in almost every industry to provide machine readable information about an item or product and to help track such items. Numerous different symbologies have been developed, such as one dimensional linear codes and 2D codes, such as Data Matrix. Typical linear codes comprise a series of parallel lines of varying thickness and spacing which are arranged in a linear configuration to represent a digital code containing information relating to the object. The use of bar codes has expanded due to the fact that the imaging and tracking process eliminates human error and can be performed quickly.  
         [0006]     The amount of information a bar code can contain is dependent upon the size of the markings employed in the bar code, which determines the density of the code. Linear bar codes such as UPC codes, are only recorded in one dimension. On the other hand, 2D symbologies are encoded in two dimensions to contain grater information density.  
         [0007]     In a typical reading process, a spot of light from a laser is projected and swept across the code, and the reflected light is sensed by a photosensitive element. In conventional images, lasers are used as the source illumination. Scanners may be either installed in a fixed location or portable hand-held units.  
         [0008]     Hand-held scanners must be designed to operate in situations where the number of varying factors is greater than for fixed scanners. For instance, the distance between the scanner and the bar code, the amount of illumination, the focusing of the scanner, the orientation of the scanner relative to the bar code, and the angle of the scanner relative to the bar code are all factors which must be considered for the scanner to operate correctly. For instance, U.S. Pat. No. 5,296,690 to Chandler et al discloses a system for locating and determining the orientation of the bar codes in a two-dimensional image. The Chandler et al patent is primarily concerned with making sure that the scan of the bar code is performed correctly with regard to the orientation of the scanner and the bar code.  
         [0009]     Some hand-held scanning devices have a wand-like configuration where the device is intended to make contact with the code as it is swept across the code. Such a wand eliminates the variation in the distance between the scanner and the code and therefore requires no focusing.  
         [0010]     Two-dimensional arrays such as charge coupled device (CCD) arrays have been used to create the image of the bar code as it is scanned, but traditionally a laser and a single photodiode are used for scanning a linear bar code. A CCD having dimensions of 640 by 480 pixels provides sufficient resolution for use with VGA monitors, and is widely accepted. The video image is sensed in the CCD, which generates an analog signal representing the variation in intensity of the image, and an analog to digital converter puts the image signal into digital form for subsequent decoding. Two dimensional sensors are used with spatially oriented 2D codes.  
         [0011]     For a non-contact hand-held scanner, it is necessary to be able to read the bar code over a reasonable distance, to provide sufficient illumination, to focus the scanner onto the bar code and perform the entire operation in a reasonable amount of time. While it may be possible to create an imager which can perform all of the desired functions, if the imager does not operate in a manner the user finds comfortable and sufficient, then the imager will not be accepted by end users and will not commercially viable. For example, if the imager cannot perform the focusing quickly enough, then variations in the position of the scanner, due to the inability of the user to hold the imager steady, will create problems which cannot be easily overcome.  
         [0012]     By way of example, if a scanner takes too long to perform a focusing function from the moment the user depresses a trigger, then the position of the scanner relative to the bar code may vary during the focusing operation thereby requiring yet another focusing operation. Similarly, such movement in the position of the scanner relative to the bar code will change the parameters for achieving the desired illumination.  
         [0013]     Scanners which have been designed to read linear, or one dimensional, codes are, for the most part, incapable of scanning 2D symbologies. Linear and 2D symbologies may be provided on items by attaching a label to the item, putting the item in a container having a preprinted code, or by directly marking the product, such as by etching. Most conventional scanners may find it difficult to read symbologies which have been etched directly onto a product.  
       SUMMARY OF THE INVENTION  
       [0014]     These and other deficiencies of the prior art are addressed by the present invention which is directed to a hand-held imager which is capable of reading both linear one dimensional codes and two dimensional symbologies, which can perform illuminating and focusing steps quickly and accurately so as to eliminate variation in the position of the imager relative to the code, and which can operate in an environment where the imager is preferably positioned anywhere from substantially 1.5 inches to 16 inches from the targeted code.  
         [0015]     The hand-held imager of the present invention can perform omnidirectional coded symbology reading for both linear and two-dimensional symbologies over relatively long working distances. The imager includes an imaging system having a focusing system, an illumination system, and a two-dimensional photodetector which forms an image of the bar code. After achieving targeting of the coded symbology, the reader of the present invention adjusts illumination and then the focus between multiple different focuses, and utilizes a portion of the two-dimensional photodetector to determine the optimum focus. Upon the determination of optimum focus, the focusing system is configured at the optimum focusing configuration established in the initial focusing step, and an image is created using the entire two-dimensional photodetector.  
         [0016]     A targeting system visually assists the user to position the reader so that the coded symbology, being targeted, is within the field of view of the reader. The reader has two types of illumination, one for symbologies which are close to the reader, and a second type of illumination for symbologies which are farther from the reader. The two-dimensional photodetector may be employed to determine the optimum illumination.  
         [0017]     It is an object of the present invention to provide a hand-held reading device capable of reading both linear and 2D coded symbology.  
         [0018]     Another object of the present invention is to provide a hand-held reader which can perform an imaging operation in a range between 1.5 inches and 16 inches to the coded symbology for typical hand-held use, but may have both higher and lower distance limits.  
         [0019]     Yet another object of the present invention is to provide a hand-held reader capable of reading direct product markings in addition to coded symbology printed on labels.  
         [0020]     Still another object of the present invention is to provide a hand-held reader which utilizes a two dimensional sensor to facilitate focusing and illumination adjustment.  
         [0021]     Yet another object of the present invention is to provide a hand-held reader which utilizes a two dimensional sensor to facilitate focusing and illumination adjustment, where only a small portion of information received by the two dimensional sensor is used, to thereby speed processing.  
         [0022]     Another object of the present invention is to provide a hand-held reader made from commonly available “off-the-shelf” components.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]     The foregoing and other attributes and objects of the present invention will be described with respect to the following drawings in which:  
         [0024]      FIG. 1  is a perspective view of the reader according to the present invention;  
         [0025]      FIG. 2  is a plan view of a typical linear type coded symbology;  
         [0026]      FIG. 3  is a plan view of a Data Matrix symbology;  
         [0027]      FIG. 4  is a cross-sectional view of the reader shown in  FIG. 1  according to the present invention;  
         [0028]      FIG. 5   a  is a perspective view of a first embodiment of a focusing disk which may be employed in the focusing system of the present invention;  
         [0029]      FIGS. 5   b  and  5   c  are planar and cross-sectional views, respectively, of a second embodiment of a focusing disk which may be employed in the focusing system of the present invention;  
         [0030]      FIGS. 6   a - 6   k  represent eleven images p 1 -p 11 , where images p 1 -p 6 , shown in  FIGS. 5   a - 6   f , are used in the photonics or photometric analysis, and images p 6 -p 11 , shown in  FIGS. 6   f - 6   k , are used in the focus analysis;  
         [0031]      FIG. 7  shows a pixel plot of line  235  of a CCD for the values between 128 and 508, in the horizontal location, for images p 1 , p 6 , and p 11 , shown in  FIGS. 5   a ,  6   f  and  6   k;    
         [0032]      FIG. 7A  is a group showing local maximum and minimum points;  
         [0033]      FIGS. 8   a - 8   k  show Table A, containing data from which the pixel plots of  FIG. 7  are derived;  
         [0034]      FIG. 9  is an edge histogram for images p 1 -p 6 , shown in  FIGS. 6   a - 6   f;    
         [0035]      FIGS. 10   a - 10   g  show Table B which contains the population for each peak-to-peak value of each image p 1 -p 6 , and illustrated in  FIG. 9 ;  
         [0036]      FIG. 11  is a table showing the entropy score, maximum pixel value and minimum pixel value for each image p 1 -p 6 ;  
         [0037]      FIGS. 12   a  and  12   b  are frequency histograms for images p 6 -p 11 , shown in  FIGS. 6   f - 6   k , with  FIG. 12   b  being an enlargement of a portion of  FIG. 12   a;    
         [0038]      FIGS. 13   a - 13   g  show Table C which contains the delta peak value of each image p 6 -p 11 ;  
         [0039]      FIG. 14  is a chart showing the entropy score, maximum pixel value and minimum pixel value for each image p 6 -p 11 ; and  
         [0040]      FIG. 15  is a block diagram of the imager according to the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0041]     The hand-held reader  10  shown in  FIG. 1  is capable of reading coded symbologies omnidirectionally, and producing decoded data. The scanning device  10  is self-sufficient and does not require an external power source, except for host power provided through an interface cable  14 . The scanner  10  can read both linear bar codes  40 , as shown in  FIG. 2 , and matrix or 2D coded symbologies  54  as shown in  FIG. 3 .  
         [0042]     The linear or 2D coded symbologies are standard symbologies well known in the art, and the decoding of them is similarly well known. However, unlike conventional scanners, the reader  10  of the present invention can read both types of symbologies, can operate over a wide range of distances, 1.5 to 16 inches, and is hand-held. To achieve these results, the reader  10 , upon activation by the user, must be able to target the coded symbology, determine the optimum illumination, determine the optimum focus, and make an image of the targeted code symbology in an extremely short period of time in order to eliminate possible degrading variations.  
         [0043]     For example as the user holds the reader  10  relative to a linear bar code  40  or a 2D coded symbology  54 , the reader can move relative to the code thereby changing the focus, illumination and angle of the scanner relative to the code. By performing the entire image capture function as quickly as possible, from the moment targeting is achieved, such variables are minimized. How such rapid image focusing, illumination and capture are performed will be described in detail below.  
         [0044]     The reader  10  includes an ergonomic housing  12  designed to fit comfortably in a user&#39;s hand. The reader  10  decodes the data, and forwards the decoded data to a computing device platform, such as a PDT, PLC or PC, which performs information gathering as one of its functions. A switch or trigger  15  protrudes through the top of the housing  12  for activation by the user&#39;s finger. Lights  18  and  20  are provided on the top of the housing  12  and indicate the active status and successful imaging of the coded symbology, respectively. Audible signals may also be provided.  
         [0045]     The hand-held imager  10  utilizes an aiming device to locate the target symbologies in the field of view (FOV). The method of targeting is designed to minimize power consumption. A programable two-phase trigger is used to acquire the target symbology.  
         [0046]     A window  22  having a clear aperture section  24  is provided on the front of the housing  12 . A targeting line  32  is produced by a light source in the hand-held imager  10  and is projected onto the targeted coded symbology to ensure that the coded symbology  40  or  54  is within the field of view of the imager  10 . The targeting line  32  is preferably a color, such as red, which is discernable from the ambient light sources.  
         [0047]     In operation, the user presses the trigger  15  to a first position thereby causing the projection of the targeting line  32  onto the coded symbology. The targeting line  32  is then used to position the imager  10  and the coded symbology relative to one another. The imager  10  then adjusts the illuminating light if necessary, and determines the correct focus. The light  18  is illuminated to indicate to the user that imaging is underway. Upon completion of the imaging process the light  20  turns on to provide the user with an indication of successful scanning.  
         [0048]     Referring to  FIGS. 2 and 3 , a linear code  40  and Data Matrix code  54 , respectively, are shown. Typical 2D or Data Matrix symbologies are smaller than linear codes and may be etched directed onto the product. The information is typically encoded in feature sizes of 5, 7.5, or 10 mils. As a result, the imager  10  needs to be much closer when reading 2D symbologies  54  than for linear codes  40 .  
         [0049]     The imager  10  is shown in cross-section in  FIG. 4 , where the optical system  80  is illustrated as including objective taking lens  92  and focusing disk  94 . The disk is driven rotational at 600 RPM about axis  91  by the motor  96 . The rotational axis  91  is offset from the optical axis O A  of the imaging system  80 . A dark field illuminator  82  having multiple light emitting elements  98 , such as LEDs, which illuminate rearwardly onto a non-transparent wall, which then provides diffuse light to the window  22 . A bright field illuminator  84  is provided with multiple light emitting elements  100  for radiating forward directly through the window  22 . Dark field illumination is provided for direct product marking (low contrast), while bright field illumination is used primarily for high contrast label marks.  
         [0050]     Built-in bright field and dark field illumination are provided to achieve proper contrast for reading the symbologies on direct product marked parts at close-in distances. Only bright field illumination is used at greater working distances. The details of the illumination system are set forth in co-pending commonly owned patent application Ser. No. 09/151,765) filed on Sep. 11, 1998.  
         [0051]     A key aspect of the present invention is the CCD detector  93 , positioned along the optical axis O A.  The CCD detector  93  is rectangular and has a VGA pixel density. In the preferred embodiment, the CCD detector  93  is an interline 659×494 progressive scan, monochromatic CCD, which may be manufactured by Panasonic Corporation, model #MN37761AE, or a 659×494 pixel CCD manufactured by Sony Corporation, mode #ICX084AL. Both of the foregoing CCD&#39;s provide 640×480 resolution commonly used in VGA monitors. While the preferred embodiment illustrated therein utilizes a CCD, other array detectors such as CMOS, or other sensors may be used. Furthermore, the CCD need not be limited to 640×480 and may have other sizes.  
         [0052]     The hand-held imager  10  can decode multiple symbologies on any background, including etched metal and printed ink jet. The paramount reading capability for use on surfaces that are direct product marked is the Data Matrix symbology.  
         [0053]     A first embodiment of the focusing disk  94 , shown in cross-section in  FIG. 4 , is shown in greater detail in  FIG. 5   a . The disk  94  has a series of different thickness optical positions  132 . The thickness of the optical positions  132  is varied to focus the objective lens  92  onto the CCD detector  93  during image capture. The illustrated embodiment shows twelve optical positions  132  which thereby provide twelve potential focus ranges. A positional encoding strip  134  is provided on the disk  94  so that the position of the disk can be tracked. However, it is noted that the invention could operate with at least two optical positions.  
         [0054]     Referring to  FIGS. 5   b  and  5   c , planar and cross-sectional views of a second embodiment of the focusing disk  94  is shown. The second embodiment has eight optical positions  132  and further includes an outer circumferential wall  136  which provides additional structural support.  
         [0055]     The CCD detector  93  is utilized to determine which optical plate  132 , and therefore which focusing zone, is appropriate for a particular coded symbology scan. As the disk  94  is rotated, the illuminating light is reflected back through the objective lens  92  through each of the optical positions  132  and onto the CCD detector  93 . In order to minimize the time it takes to focus the imager  10 , only a fraction of the pixels of the CCD detector  93  are employed in the determination of the optimum optical plate, and thereby the focused optical plate.  
         [0056]     From start up, the imager  10  produces target illumination, then takes approximately 25 to 30 milliseconds to reach the rotational speed of 600 RPM. The CCD then powers up and then resets. Multiple, up to five, images are taken for photometry, and multiple images are taken for focusing. Each image requires exposure time and shift out time, which is in the range of, but no greater than 5.5 mS. After the optimum optical plate is repositioned in the optical path, CCD detector must capture and shift out the entire image in about 31.4 milliseconds. The total time for the entire operation is therefore less than half a second, which is sufficient to minimize the variable factors discussed previously.  
         [0057]     The aforementioned variations are more detrimental to photometry than to focus analysis. In order to minimize the variations, the present invention employs a number of techniques to accelerate the operation. First, the imager operates in a “fast mode.” A small size slice of an image, 384 by 10, is utilized, 384 being over 60% of the image width, and 10 scan lines is more than two times the minimum cell size requirement (4 pixels). This ensures that a transition will be encountered in the image slice, while having as small a size as feasible. The search for the proper exposure time uses seven images, but the use of only five images is contemplated, which will require no more than 30 mS. The optical disk  94  can be separated into two groups of optical positions  132 , for Dark Field and Bright Field images.  
         [0058]     The maximum time to decode a printed label is 350 milliseconds, while the maximum time to decode a direct product marked code is 400 milliseconds. The foregoing times include the time, from when the trigger is activated, to illuminate, focus, acquire the image, decode the symbology, and output the decoded data.  
         [0059]     If all 325, 546 pixels of the CCD detector  93  were used for each optical plate  132  of the focusing disk  94 , the image capture procedure would take far too long. To minimize the time required to obtain data for each optical plate  132 , only a portion of the CCD detector  93  is used. In operation, the CCD detector  93  generates image data as 494 lines, one line at a time, each line being 659 pixels long. The first 246 lines, instead of being digitized which would require significant time, are “dumped.” Furthermore, to accelerate the process, the speed at which the data is set through the CCD is much faster than the speed used for normal image capture. Since the information contained in the first 245 lines is not important to the focusing steps, the degradation of such information, due to the accelerated reception, is not a detriment.  
         [0060]     The next ten lines, lines  247 - 256  are utilized in the analysis described below, and then the CCD detector  93  is reset, never reading lines  257 - 494 . In this matter, the focusing time is more than halved.  
         [0061]     Referring to  FIG. 15 , a block diagram of the imager  10  of the present invention is illustrated. The CPU  200  connects to the flash memory  202  and DRAM  204 , which together form the computing engine for the imager  10 . The CPU  200  further connects to the serial interfaces  206 , which in turn is connected to the power supply  210 , switches  214 , motor  215  and illumination drivers  218 . The illumination drivers  218  are connected to the Bright Field and Dark Field and Targeting Illumination, shown as Illumination  224  in  FIG. 15 . An FPGA  220  is connected to the CPU  200 , the flash memory  202 , DRAM  204 , illumination drivers  218  and CCD  222 . The FPGA  220  controls the CCD and the Illumination  224 . The FPGA  220  and microcontroller  212  control the targeting. The Motor  216  dries the focusing disk  94 .  
         [0062]     In order to evaluate the image data for each optical plate  132 , the ten middle lines of data need to be analyzed. The transitions between light and dark areas of the code are critical for such analysis. Furthermore, it is important to note that in the determination of which optical plate provides the best focus and illumination, the quality of the images relative to one another is what is important, not the absolute image quality. The imager  10  is designed to achieve correct decoding of the coded symbology targeted with the minimum necessary focusing, not perfect focusing which would require considerably more time and/or complexity.  
         [0063]     As an example we will traverse a scan line from left to right. For the examples in  FIGS. 7-14  we used a minimum peak to peak value of 12. This means that a relative white pixel must be greater than a relative black pixel by a magnitude of 12 for it to be considered a white pixel relative to that black pixel, but other values may be used depending on the application. We will first look for a local minimum. We choose a new minimum when the current pixel is less than the previous minimum. We stop looking for a minimum and start looking for a maximum when we find a pixel that is less than or equal to the current maximum minus 12. When this occurs we have a local minimum, a local maximum, the magnitude of the difference and the number of pixels between the minimum and maximum points. The magnitude of the difference or peak to peak value is used as the index to the bin number of the edge histogram that should be incremented by one. the number of pixels between the peaks is used as the index to the bin number of the frequency histogram that should be incremented by one. This sequence is repeated for the remainder of the scan line.  
         [0064]     Referring to  FIG. 7   a , point A is the first local maxima. Point B is the first local minima. Point C is an inflection recognition point, meaning you know you are done looking for a local minima because you are more than 12 above the value at point B. You can then evaluate the pair AB. For the pair AB, the frequency corresponds to |X(A)-X(B)|, while the peak to peak value corresponds to |Y(A)-Y(B)|. Point D is not a local minima because it is not at least 12 less than point C 1 , an inflection point between points B and D. Point E is the second local maxima, point F is the inflection recognition point for the pair BE. Point G is the second local minima and point H is the third inflection recognition point corresponding to the pair EG. Point I is the third local maxima.  
         [0065]     For illustrative purposes,  FIG. 7  shows a pixel plot of line  235  of the CCD for the values between 128 and 508, in the horizontal location, for images p 1 , p 6 , and p 11 , shown in  FIGS. 6   a ,  6   f  and  6   k . The three images are shown by three different lines, p 1  is shown by the solid line, image p 6  is shown by the dashed line, and image p 11  is shown by the dotted line.  
         [0066]     The data from which the pixel plots of  FIG. 7  are drawn is shown in Table A, shown in  FIGS. 8   a - 8   k , and includes the values for each horizontal location within the field. From  FIG. 7 , it can be clearly seen that the image p 6  has the best transitions.  
         [0067]     Illumination analysis is performed by developing entropy scores for each illuminating condition. The quality or nature of the transitions (peak-to-peak) values are taken into account by this analysis. In an edge histogram the y axis is the population or number of transitions, and the x axis represents the peak-to-peak value.  
         [0068]      FIGS. 6   a - 6   k  represent eleven images p 1 -p 1 . Images p 1 -p 6 , shown in  FIGS. 6   a - 6   f , are used in the following photonics or photometric analysis, and images p 6 -p 11 , shown in  FIGS. 6   f - 6   k , are used in the following focus analysis.  
         [0069]     Referring to  FIG. 9 , an edge histogram is illustrated for images p 1 -p 6 , shown in  FIGS. 5   a - 6   f .  FIGS. 10   a - 10   e  show Table B which contains the population for each peak-to-peak value of each image p 1 -p 6 . The images p 1 -p 6  are illustrated by different shaded areas in  FIG. 9 . The peak-to-peak values begin at 12, since, as shown in  FIG. 10   a , the first population value does not occur until 12 for image p 1 . Similarly,  FIG. 9  ends with value  118  for image p 6 . The remaining values up to 255 are all zeros in the example shown in  FIG. 9 , and therefore are not illustrated. The entropy score, maximum pixel value and minimum pixel value for each image p 1 -p 6  are shown in  FIG. 11 , with the entropy score being the total of the population values for each image. The entropy values individually have no meaning. Rather, a comparison of the entropy values with one another shows which image has the highest entropy value. Here it is image p 6  with a value of 758. With reference to  FIG. 9 , it is clear that image p 6  has the largest area under its curve, which is represented by the entropy value. From the foregoing, it can be seen that image p 6  has the best illumination.  
         [0070]     The maximum and minimum pixel values are obtained from the average of the brightest 20 and the average of the dimmest 20 values, respectively. These maximum and minimum pixel values can be used to determine if the image meets minimum criteria for usability.  
         [0071]     The entropy score is not used by itself, and in particular when an image is over-saturated. In that instance, the signal has reduced the peak-to-peak values, and has fewer edges than an under-saturated image.  
         [0072]     To perform the optical plate focus analysis the microprocessor concerns itself with the rate of change of energy between neighboring pixels of image data. If all transitions are plotted in a two dimensional histogram, a graph can be generated to produce a score for determining the optimum focus. The x axis represents the number of pixels between local maxima and minima, and the y axis represents the population.  
         [0073]      FIGS. 12   a - 12   b  are frequency histograms for images p 6 -p 11 , shown in  FIGS. 6   f - 6   k . The number of pixels between peaks are plotted on the x-axis in a range of 1 to 123. 123 is the highest value having a population, for image p 6 , as shown in Table C in  FIGS. 13   a - 13   g , which provides the population values for the number of pixels between peaks. Reviewing  FIG. 12   a , it can be clearly seen that most of the data appears in the first 25 values on the x-axis, and therefore these values are shown in the enlarged portion of the histogram shown in  FIG. 12   b.    
         [0074]     A focused image has a sharp contrast between light and dark areas. An out of focus condition is represented by the loss of high frequency components. Therefore, the image with the highest population density at high frequency indicates the best focus. The data represented in  FIGS. 12   a  and  12   b  is shown in Table C of  FIGS. 13   a - 13   g . Unlike illumination, the determination of the optimum focus does not use the entire population. Rather, only the first seven values are used to develop the entropy scores, shown in  FIG. 14 . Since slow edges are represented by low frequency values, only the first seven values are needed. According to  FIG. 14 , image p 6  has the highest entropy score of 894, indicating that it is the best focused image.  
         [0075]     During image capture and decoding operations, the imager  10  draws approximately 200-500 milliamperes of constant power at 4.2-5.25 V. Where the imager  10  interfaces with a portable data terminal (PDT), 4 to 6 V is normally specified at 200-500 mA, while the universal serial bus (USB) interface is specified at 4.2 to 5.25 volts at 100-500 mA.  
         [0076]     Having described the preferred embodiments of the hand-held imager in accordance with the present invention, it is believed that other modifications, variations and changes will be suggested to those skilled in the art in vie of the description set forth above, such as utilizing different focusing disk configurations, or other focusing configurations such as quintic lens. It is therefore to be understood that all such variations, modifications and changes are believed to fall within the scope of the invention as defined in the appended claims.