Abstract:
A method, system, and computer readable medium are disclosed for detecting and removing defects using images captured at multiple orientations. Defects in a physical medium in which an image is formed can hamper attempts to record representations of the original image. To lessen the effects of these physical defects on captured images, multiple images are captured using multiple different orientations of the physical medium in which the image is formed. The physical defects obscure different image information when viewed from different angles. By capturing images at multiple orientations and combining these images, almost all of the desired image information from the original image can be recovered, despite imperfections in the physical medium. The present invention finds application in image capturing devices, such as flatbed scanners, photocopiers, and the like.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims benefit under 35 U.S.C. §119 of the following U.S. provisional patent applications: Serial No. 60/235,158, entitled Multiple-Orientation Image Defect Detection and Correction, which was filed on Sep. 22, 2000. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to image capturing and processing, and more particularly to detecting and correcting image defects.  
         BACKGROUND OF THE INVENTION  
         [0003]    Document copiers, facsimile machines, image scanners, optical character recognition systems, and many other modern devices depend on accurately capturing an image formed in a physical medium. Toward that end, scientists and engineers have implemented a great number of improvements in the field of image processing in general, and the acquisition of electronic images in particular.  
           [0004]    However, even with advances in imaging technology, improved solutions to some common problems would be welcome. For example, media in which images are formed may have defects caused by various processes, such as production of the image medium, or the storage and transportation of the physical image medium. These defects are an ongoing problem for both professionals and amateurs attempting to capture high quality images using commonly available image capturing devices, such as scanners, because the defects can degrade the quality of the captured images. The propagation of defects to captured images can significantly reduce the visual appeal of the images, or make the information contained in the physical medium more difficult to interpret.  
           [0005]    Many image processing systems do not have the facility to detect and correct defects in captured images resulting from defects in the physical medium from which the images are captured. Image processing systems that do have the capability to detect and correct defects often require special add-on hardware or modifications that may make the use of such systems more expensive than unmodified image capturing devices. It would be beneficial if imperfections and defects in image media could be corrected using commonly available, inexpensive image capturing devices.  
         SUMMARY OF THE INVENTION  
         [0006]    What is needed, therefore, is a way to detect and remove defects in captured images resulting from imperfections in a physical medium without requiring special or additional hardware for an image processing system. Accordingly, at least one embodiment of the present invention provides a method for capturing an image formed in a physical medium having imperfections. One such method comprises positioning a physical medium in relationship to an image capturing device such that the physical medium has a first orientation, and capturing at least a first captured image representative of the image formed in the medium, at the first orientation. The method further comprises positioning the physical medium in relationship to the image capturing device such that the physical medium has a second orientation, different from the first orientation, and capturing at least a second captured image representative of the image formed in the physical medium, at the second orientation. Additionally the method comprises analyzing the captured images to identify portions of the captured images corresponding to imperfections in the physical medium, and forming a corrected image by removing, at least in part, the identified portions of the captured images corresponding to imperfections in the physical medium. Another method according to an embodiment of the present invention comprises positioning the physical medium in relationship to the image capturing device at least an additional time, such that the physical medium has at least a third orientation different from the first orientation and second orientation. The method further comprises capturing at least a third captured image representative of the image formed in the physical medium in at least the third orientation.  
           [0007]    Another embodiment of the present invention provides a computer readable medium tangibly embodying a program of instructions. The program of instructions includes instructions capable of storing, at least temporarily, a first captured image representative of an image formed in a physical medium, where the physical medium has a first orientation when the first captured image is captured. The program of instructions additionally includes instructions capable of storing, at least temporarily, a second captured image representative of the image formed in the physical medium, where the physical medium has a second orientation when the second captured image is captured. The program of instructions further has instructions capable of analyzing the captured images to identify portions of the captured images corresponding to imperfections in the physical medium, and forming a corrected image by removing, at least in part, the identified portions of the captured images corresponding to imperfections in the physical medium.  
           [0008]    Yet another embodiment of the present invention provides an image processing system comprising at least one communications interface capable of receiving information from an image capturing system. The image processing system further comprises at least one processor and memory operably associated with the processor. Additionally, the image processing system comprises a program of instructions capable of being stored in the memory and executed by the processor. The program of instructions includes instructions capable of storing, at least temporarily, a first captured image representative of an image formed in a physical medium, with the physical medium having a first orientation when the first captured image is captured. The program of instructions additionally is capable of storing, at least temporarily, a second captured image representative of the image formed in the physical medium, with the physical medium having a second orientation when the second captured image is captured. The program of instructions is further capable of analyzing the captured images to identify portions of the captured images corresponding to imperfections in the physical medium and forming a corrected image by removing, at least in part, the identified portions of the captured images corresponding to imperfections in the physical medium.  
           [0009]    An advantage of at least one embodiment of the present invention is that equipment costs may be reduced, because common image capturing devices may be used without requiring additional hardware.  
           [0010]    Another advantage of at least one embodiment of the present invention is that reproductions of images contained on physical media can show improved detail over the originals.  
           [0011]    Yet another advantage of the present invention is that the quality of images reproduced from captured images can be improved over conventionally reproduced images.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    Other objects, advantages, features and characteristics of the present invention, as well as methods, operation and functions of related elements of structure, and the combinations of parts and economies of manufacture, will become apparent upon consideration of the following description and claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures, and wherein:  
         [0013]    [0013]FIG. 1 is a block diagram of an image processing system according to one embodiment of the present invention;  
         [0014]    [0014]FIG. 2 is a diagram illustrating a preferred embodiment of an image capturing system according to at least one embodiment of the present invention;  
         [0015]    [0015]FIG. 3 is a cross-sectional diagram of a physical medium having a first orientation, and illustrating how defects can cause a loss of image information in captured images;  
         [0016]    [0016]FIG. 4 is a cross-sectional diagram of the physical medium shown in FIG. 3, except at a different orientation, and illustrating how, as a result of having a different orientation, the same defect can cause a loss of a different portion of image information during an image capture according to one embodiment of the present invention;  
         [0017]    [0017]FIGS. 5 and 6 are diagrams illustrating two different orientations of a physical medium on a platen of an image capturing device according to one embodiment of the present invention;  
         [0018]    [0018]FIG. 7 is a top view of a media holder according to one embodiment of the present invention;  
         [0019]    [0019]FIGS. 8 and 9 are flowcharts illustrating a method according to one embodiment of the present invention;  
         [0020]    [0020]FIGS. 10 and 11 are diagrams illustrating two different orientations of a physical medium illuminated by a light source according to one embodiment of the present invention;  
         [0021]    [0021]FIG. 12 is a diagram of a defect map according to one embodiment of the present invention  
         [0022]    [0022]FIGS. 13 and 14 are histograms illustrating pixel intensity when a physical medium is illuminated in two different orientations according to one embodiment of the present invention;  
         [0023]    [0023]FIG. 15 is a histogram illustrating a maximum pixel intensity for a pixel location according to one embodiment of the present invention;  
         [0024]    [0024]FIG. 16 is a histogram illustrating a minimum pixel intensity for a pixel location according to one embodiment of the present invention;  
         [0025]    [0025]FIG. 17 is a histogram illustrating the subtraction of the maximum pixel intensities from the minimum pixel intensities according to one embodiment of the present invention; and  
         [0026]    [0026]FIG. 18 is a histogram illustrating a defect region according to one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    FIGS.  1 - 18  illustrate a system and method that can be used to detect and remove defects from images as described in greater detail below. A method according to the present invention makes use of two or more different orientations of a physical medium with respect to the light source of an image capturing system, to detect and correct defects in the physical medium that have propagated to the captured images. The physical medium may be rotated to different orientations manually, by use of an automated mechanism, or by other appropriate methods, and images representing each orientation of the physical medium can be recorded. The defects are detected using differences between two or more captured images resulting from the uneven surface of defects in the physical medium. Since multiple images are recorded at different orientations, the detected defects in the resulting image can be corrected by combining image information from the different images.  
         [0028]    The word “light,” as used herein, refers to electromagnetic energy, and preferably electromagnetic energy with frequencies generally in the range of 10 12  Hz to 10 17  Hz, and includes visible light, which is generally in the range of 4×10 14  Hz to 7×10 14  Hz (or approximately 430 nm to 750 nm) as well as portions of the infrared and ultraviolet spectrum. The word “defect,” as used herein, refers to an imperfection on or in the physical medium, which can be, but is not limited to, a scratch, a crease, a fold, or dust on the surface of the physical medium. The word “defect” may also refer to imperfections on or in the scanning equipment, such as scratches, smudges, fingerprints, or dust on the platen. Other characteristics of a physical medium or scanning equipment that can obscure or distort a captured image of the physical medium may also be considered “defects.” For example, matte finishes on photographs, while not imperfections, tend to produce lines in a digital image when scanned, and therefore may also be considered to be a “defect” in the physical medium. The word “orientation,” as used herein, refers to the angular position of the physical medium relative to a point of reference such as the platen of a scanning device or the scanning device itself. The term “image capturing system” refers to a combination of hardware and software used to capture images representing a physical medium and store them in an appropriate manner. The term “processing system” refers to a combination of hardware and software that is used to manipulate electronic images captured by the aforementioned image capturing system to suit the preferences of the user. The term “image processing system” is used to refer to a system that may include an image capturing system and a processing system.  
         [0029]    An image processing system  100  according to one embodiment of the present invention is depicted in FIG. 1, and comprises processing system  190  and image capturing system  200 . Processing system  190  comprises a central processing unit (CPU)  105 , such as a conventional microprocessor, and a number of other units interconnected via at least one system bus  110 . In one embodiment, processing system  190  and image capturing system  200  are separate systems interconnected for functionality. For example, processing system  190  may be a desktop computer, and image capturing system  200  may be a flatbed scanner. In this example, the scanner is configured to depend upon the desktop computer for image processing and control functions. In another embodiment, processing system  190  and image capturing system  200  are part of a single physical unit, such as a xerographic reproduction machine, a facsimile machine, an optical character recognition system, a flatbed scanner, etc.  
         [0030]    One embodiment of processing system  190  is shown in FIG. 1. In this embodiment, processing system  190  is shown as an integral part of image processing system  100 , and includes random access memory (RAM)  115 , read-only memory (ROM)  120  wherein the ROM  120  could also be erasable programmable read-only memory (EPROM) or electrically erasable programmable read-only memories (EEPROM), and input/output (I/O) adapter  125  for connecting peripheral devices such as disk units  130 , tape drives  135 , CD recorders  136 , or DVD recorders  137  to system bus  110 , a user interface adapter  140  for connecting keyboard  145 , mouse  150 , speaker  155 , microphone  160 , and/or other user interface devices to system bus  110 , communications adapter  165  for connecting processing system  190  to an information network such as the Internet, and display adapter  170  for connecting system bus  110  to a display device such as monitor  175 . Mouse  150  has a series of buttons  180 ,  185  and is used to control a cursor shown on monitor  175 . Image processing system  100  includes both processing system  190 , and image capturing system  200 . It will be understood that processing system  190  may comprise other suitable data processing systems without departing from the scope of the present invention.  
         [0031]    Referring next to FIG. 2, image capturing system  200  is illustrated according to one embodiment of the present invention. Image capturing system  200  incorporates a transparent platen  220  on which a physical medium  222  to be copied can be located. In one implementation, one or more arrays  224  are supported for reciprocating scanning movement below platen  220 . In yet another implementation, additional arrays (not shown for ease of illustration) may be positioned above and below platen  220 , and may or may not be configured to move along platen  220 . A scanning system assembly  250  includes several optical components, which may move together as a single unit. In one embodiment, the scanning system assembly  250  includes a light source  234 , an associated reflector  226  and a baffle  236 , with the latter two elements cooperating to direct a narrow band of light onto a small area across the platen  220 . Also included in the assembly  250  is lens  228 , and mirrors  230 ,  238  and  240 , which operate together to focus the light band reflected from the document being scanned, through lens  228  and filter  244 , and onto array  224 . Array  224  is shown as a single item for simplicity. In actual practice it is compose of at least three sensors each with a corresponding filter specific to a color, red, green, or blue. Array  224  produces electrical image signals representative of physical medium  222 . These signals may be output to disk units  130 , tape units  135 , RAM  115 , display adapter  170  for display on monitor  175 , or to another device coupled to processing system  190  via a network for image processing.  
         [0032]    Array  224  may be a linear array of photosensitive sensors such as charge coupled devices, photo-diodes, complementary metal-oxide semiconductor (CMOS) devices, or any suitable photodetector that operates to sense light reflected from or transmitted through an image formed in physical medium  222  during the illumination period. The photosensitive sensors produce electrical signals indicative of the amount of light sensed. These electrical signals may be output for use by CPU  105  in assimilating an electronically stored representation of physical medium  222 , or measurement of an attribute of physical medium  222  such as image density. Array  224  generally extends in a direction transverse to that of the motion of scanning system assembly  250 . This enables scanning system assembly  250  to move along an axis known to those skilled in the art as the “slow scan” axis, which begins at one end of physical medium  222  and extends in the process direction toward the opposite end. The direction across the page in which the array extends is known as the “fast scan” axis. It will be appreciated that, in some cases, only some parts of image capturing system  200 , such as mirrors  230 ,  238 ,  240  are the only parts that may move in the process of scanning a physical medium. Additionally, it will be appreciated that movement of scanning system assembly  250  is described relative to a document being scanned, and that the physical medium may be moved rather than the scanning assembly. Therefore, while reference might be made herein to “movement” of one or more specific system elements and/or in a particular manner, any such references include any relative repositioning of applicable elements whereby capturing is provided in a manner consistent with at least one embodiment of the present invention.  
         [0033]    Referring to FIGS. 3 and 4, the interaction of light with a physical defect in an image containing medium is discussed. In FIG. 3, physical medium  222  is positioned in a first orientation. Light  310  emitted from light source  234  of the image capturing system  200  (as shown in FIG. 2) is reflected by physical medium  222  and is captured by the image capturing system  200  as discussed earlier. The raised surface of defect  300 , in effect casts a shadow that prevents light  310  from reaching first area  320 . Since light  310  is not reflected from first area  320 , the captured image does not have a complete representation of physical medium  222  in first area  320 . When physical medium  222  is positioned in a second orientation as shown in FIG. 4, defect  300  no longer prevents light  310  from light source  234  from illuminating first area  320 . However, in the second orientation, defect  300  prevents light  310  from reaching second area  410 , thereby obscuring a different area of physical medium  222  than was obscured when physical medium  222  was positioned in the first orientation. By capturing images at multiple orientations of physical medium  222 , substantially all of the image information can be recorded, even image information that would normally be obscured by defect  300 . Light  310  reflected from the top of defect  300  may also have special characteristics, and this information may be used to detect and correct defects. In effect each captured image contains information about the physical medium that the other images may lack. The information that the two images contain may be combined to remove the effects of defect  300  to produce a resultant image with fewer defects. Note that the change in orientation of physical medium  222  is relative to the light source  234 , but in fixed illumination source systems, the orientation of physical medium  222  can be changed by moving physical medium  222  relative to an image capturing system  200 . Physical medium  222  may be positioned in particular orientations by employing one or more of the methods discussed below, as well as other suitable methods which will become apparent upon consideration of this disclosure.  
         [0034]    In order to clarify what is meant by an image orientation, refer to FIGS. 5 and 6, in which a physical medium is illustrated in two different orientations. In FIG. 5, physical medium  222  is placed on platen  220  of image capturing system  200  in a first orientation. An image representing physical medium  222  in the first orientation may be captured and stored in image processing system  100 . Physical medium  222  is then rotated to a second orientation, as illustrated in FIG. 6 and a second image representing physical medium  222  (illustrated in FIG. 6) in the second orientation is captured. This second orientation of physical medium  222  is distinct from the initial orientation of physical medium  222 , as well as any subsequent orientations. The angle of change in orientation with respect to the first orientation may be any angle different from the first orientation, but easily attainable angles, such as 90°, 120°, or 180° are used in at least one embodiment. In the embodiment of the present invention illustrated in FIGS. 5 and 6, the physical medium is rotated manually from the first orientation in FIG. 5 to the second orientation in FIG. 6. In other embodiments, the physical medium may be rotated to different orientations using an automated mechanism.  
         [0035]    In at least one embodiment of the present invention, the program of instructions for detecting and correcting defects provides the ability to compensate for errors in the accuracy of the orientation angle introduced by the manual or automatic orienting of physical medium  222 . For example, a user or the image defect detection and correction software may dictate a difference of 90° between image captures of physical medium  222  in a first orientation and a second orientation. However, human or mechanical error causes a difference of only 85° between the first orientation and second orientation. Since the error between the desired difference angle (90°) and the actual difference angle (85°) is within the compensation range (for example ±5°) of the image defect detection and correction software, therefore the software is capable of compensating for this error. Although a compensation range of ±5° is discussed, other compensation ranges may be used without departing from the spirit or the scope of the present invention.  
         [0036]    Referring to FIG. 7, one embodiment of an automated positioning mechanism is illustrated, and designated generally as media holder  700 . Media holder  700  incorporates chassis  710 , rotating carriage  730 , transparent platen  720 , and channel  715 . In at least one embodiment of the present invention, media holder  700  may be an integral element of image capturing system  200  (FIG. 2). Alternatively, media holder  700  may be a device that can be placed on a conventional image capturing device such as a scanner, copier, optical character recognition system, and the like. Media holder  700  rotates physical medium  222  located on transparent platen  720 , which is in turn located in rotating carriage  730 , by a desired angle relative to the orientation of a previous image capture. In use, media holder  700  is placed on platen  220  of image capturing system  200  (FIG. 2). Physical medium  222  is placed on transparent platen  720 , which is in turn located in the rotating carriage  730 . Rotating carriage  730  is connected to chassis  710  by means of channel  715 , allowing rotating carriage  730  and transparent platen  720  to rotate about the central axis of rotating carriage  730 . Tick marks  725  indicating degree of rotation from point  740  are located on the surface of chassis  710  proximal to rotating carriage  730 . Position indicating mark  735 , located on the surface of the rotating carriage  730 , is used to indicate relative orientation from point  740  using tick marks  725 . Alternatively, one may practice the present invention by rotating the image capturing system  200  in relation to the physical medium  222  thus causing a change in the orientation of physical medium  222  to image capturing system  200  between image captures. Other suitable methods of positioning physical medium  222  at different orientations may be applied consistent with the principles set forth herein.  
         [0037]    Referring next to FIGS. 8 and 9, a method of practicing at least one embodiment of the present invention is illustrated. The method commences at step  800 , where physical medium  222  is placed on platen  220  of image capturing system  200  (as shown in FIG. 2) in a first orientation. Alternatively, if the use of a mechanism to rotate the physical medium is desired by the user, physical medium  222  can also be placed on transparent platen  720  of media holder  700  (as shown in FIG. 7). In step  810 , an image of physical medium  222  in the first orientation is captured by image capturing system  200  and may be recorded in processing system  190 . As noted earlier, in at least one embodiment, both image capturing system  200  and processing system  190  are part of image processing system  100 . The method then proceeds to step  820 . In step  820  physical medium  222  is rotated to a second orientation, different than the previous orientation of physical medium  222  in step  800 . The second angle may be any angle different from the first angle, but easily attainable angles such as 90°, 120°, or 180° may be used in at least one embodiment. The physical medium may be rotated manually by a user, automatically positioned by a mechanism such as that shown in FIG. 7, or positioned using other suitable methods. In step  830 , a second image of physical medium  222  in a second orientation is captured and stored in the same manner as the first image was captured in step  810 . The decision to capture additional images of physical medium  222  is made in step  840 . Additional images may be used to improve the quality of a desired image by providing additional image information that may be used in combination with the first image and the second image to improve the resultant image&#39;s resolution, improve defect detection and removal, or otherwise facilitate image reproduction.  
         [0038]    If additional images of physical medium  222  are to be captured, steps  820 - 840  may be repeated the desired number of times until all desired images of physical medium  222  in the desired number of different orientations are captured. As noted earlier, the additional orientations may be any angle different from the angles of the previous orientations of physical medium  222 , but easily attained angles, such as 90°, 120°, and 180° may be used. While it is desirable to capture images at different orientations, some embodiments of the present invention record multiple images at a single orientation, in addition to capturing images at different orientations. If no additional images are to be captured, the method proceeds to step  850 , illustrated in FIG. 9.  
         [0039]    Note that in at least one embodiment, images are captured and processed using data sets obtained from a plurality of pixels detected by a image capturing device. A pixel is the smallest individual, discrete element of a captured image. For color images, scanned pixels generally contain multiple samples; one for each color sub-sample, such as red, green and blue. Often each pixel is represented in the image processing system by a plurality of bits. Typically, the intensity or frequency of a pixel is represented by an 8 bit byte. The greater the number of pixels per unit area, the greater clarity, or resolution, of the captured image. The plurality of pixels representing a captured image are represented by a data set that can be processed by an image processing system to detect and correct defects, alter coloring, and the like.  
         [0040]    Referring next to FIG. 9, a continuation of the flowchart depicted in FIG. 8 is illustrated according to one embodiment of the present invention. Step  845  aligns the two or more digital images so that data from corresponding pixels may be examined and compared. In step  850 , image processing system  100  filters the digital data in the data sets for the two or more digital images captured from physical medium  222  in two or more different orientations in steps  800  to  840  (FIG. 8). In many applications, image processing system  100  may use a high-pass filter for filtering. The purpose of the filter is to reduce the effects of irregular light source shading. A variety of filters are known to reduce the effects of irregular light source shading. A useful filter is the difference between the original image and the low pass version of the image created through a Gaussian filter with a radius of five pixels.  
         [0041]    Once the data has been filtered, in steps  855  and  860 , the minima and maxima of the two corresponding pixels of each of the two captured digital images are obtained. The corresponding pixels are the pixels that are sensed from substantially the same physical location on the substrate. The maxima is the highest pixel intensity of the pixel pairs and the minima is the lowest pixel intensity of the pixel pairs. In cases where color sub-samples are captured, each pixel would have a corresponding pixel intensity value for each color. For example, if red, green, and blue samples are captured, there would be pixel intensity values for each of the red, green, and blue sample captures. In steps  855  and  860 , image processing system  100  finds the maximum and minimum amplitude intensity for the pixel pairs. By obtaining the maxima and minima, it is possible to obtain histograms of the maximum and minimum amplitude intensity. An example of these histograms are illustrated in FIGS. 15 and 16, which will be discussed later.  
         [0042]    In step  865 , the difference between the maximum and minimum pixel intensity for each pixel is obtained. Using this difference, it is possible to create a histogram of the difference between a maximum and a minimum amplitude intensity. Such a histogram is illustrated in FIG. 17. As is apparent from the histogram in FIG. 17, the difference between the minimum and the maximum is center region  1700  having a small difference value which corresponds to the center region of the defect, which on either side of center region  1700  will be a very large difference value. The large value difference exists due to the fact that light from each side of the pixel will cast a shadow in the opposite direction and therefore the difference between the minimum and the maximum pixel intensity on the opposite side of the defects will be large. Note that the operations of steps  855 ,  860 , and  865  can be implemented in a variety of different manners of those skilled in the art. It will be appreciated that the maximum of the two pixels minus the minimum of the two pixels is equivalent to the absolute value of one pixel minus the other.  
         [0043]    In step  870 , the differences of each pixel are used to create a defect map in which adjacent pixels, each indicative of a defect at the pixel level, are combined to form a region of pixels corresponding to a single defect. A method of creating a defect map according to one embodiment of the present invention is discussed elsewhere with reference to FIGS. 10, 11, and  12 . As can be seen in the difference between the histograms in FIGS. 17 and 18, clusters of pixels may be operated upon, such that the maximum pixel difference value in the cluster will be assigned to all the pixels in the cluster, so long as the pixel values do not exceed a lower threshold value  1810  such as an amplitude of 35. The lower threshold value  1810  is used to indicate that if a pixel has a value below that threshold it does not contain a defect. Lower threshold value  1810  is empirically determined. Thus, the usage of this regional maximum tends to linearize the image portion of the histogram in FIG. 18 and also provides for more accurate borders  1510  of the defect to be established. For example, the first three pixels in FIG. 17 have different amplitude values, by considering these pixels to be part of the same cluster, they may be assigned the same pixel value. This can be seen by examining the first three pixels of FIG. 18. These pixels now have the same intensity value. This allows for differences in amplitudes to be determined more accurately and therefore leads to a more accurate determination of defect borders.  
         [0044]    The area between the thresholds, considered to contain a partial defect, will be partially corrected, to avoid hard edges, as described below. While upper threshold value, with an amplitude of 75, and lower threshold value  1810 , with and amplitude of 35, have been found useful, other values can be used. It should be noted, therefore, that the defect map contains information not only relating to the presence or absence of defects but to the degree to which a defect exists. This helps, as will be appreciated by those skilled in the art, in blending together regions that do not contain a defect. While FIGS.  13 - 18  illustrate the use of histograms to locate defects, the information can also be stored and arranged in a record, file or by other convenient means.  
         [0045]    In determining defect map  1200  (FIG. 12), at least one embodiment of the present invention also applies an upper threshold value  1820  (FIG. 18) to the difference data to obtain a mask of the areas that correspond to a defect. Thus, all pixel locations that have a difference value that is greater than the upper threshold value  1820 , which in this example is 75, will be considered to contain a true defect and can be fully corrected as described according to at least one embodiment of the present invention.  
         [0046]    Next, in step  875 , information from the digital image of physical medium  222  in a first orientation and the digital image of physical medium  222  in a second orientation captured in steps  800 - 840  is combined to provide data for defect areas on defect map  1200 . In step  880  this information is used to fill in defect areas detected using defect map  1200 . Data from the surrounding areas of defect  300  in defect map  1200  in the captured images is used to fill in missing information for defect  300  in defect map  1200 . Additional image captures may provide additional data for areas of physical medium  222  (FIG. 2) affected by defects, contamination, artifacts, or other image imperfections.  
         [0047]    The method concludes in step  890 , where the resulting enhanced image with corrected defects from steps  800 - 880  is stored in a computer readable form using processing system  190 . Alternatively, the resulting image can be reproduced as a physical medium, such as a printed image or on film, transmitted via an external network such as the Internet, delivered as an electronic mail attachment, displayed on a computer monitor, or otherwise. It should be noted that defect detection and correction results may vary depending on the hardware and software components used in image processing system  100 . For example, low-end scanners (image capturing device  200 ) may not have the ability to capture images at a resolution that allows very small defects to be detected, and therefore these very small defects may not be corrected. Similarly, processing system  190 , such as a personal computer, with minimal or substandard processing power may be unable to process multiple images of a physical medium to detect and correct defects in a time considered reasonable by a user. It should also be noted that while FIGS. 8 and 9 illustrate a particular sequence of steps, other methods of practicing the present invention employ variations in the order of the illustrated steps.  
         [0048]    A method for creating a defect map for use in detecting and correcting defects according to one embodiment of the present invention is depicted in FIGS. 10, 11 and  12 . Referring first to FIG. 10, an image  1010  on physical medium  222  in a first orientation with a first defect  1020  and a second defect  1030 , such as a piece of dirt, a smudge, or a scratch, is illustrated. Also illustrated is light source  234  of image capturing system  200  (FIG. 2) on the left side of physical medium  222  in a first orientation. Light source  234  illuminates physical medium  222  and first defect  1020  and second defect  1030  at an angle from the left hand side. This produces a first defect shadow  1040  and a second defect shadow  1050  to the right of first defect  1020  and second defect  1030 . No shadow is produced by image  1010  since it is flat on physical medium  222 .  
         [0049]    Referring next to FIG. 11, an image  1010  on physical medium  222  in a second orientation different from the first orientation of FIG. 10 by 180° with a first defect  1020  and a second defect  1030  is illustrated. Light source  234  is on the right hand side of physical medium  222  due to the  180 ° change in orientation from the first orientation of FIG. 10 to FIG. 11. Light source  234  illuminates image  1010  and first defect  1020  and second defect  1030  at an angle from the right hand side. This produces a first defect shadow  1110  and a second defect shadow  1120  to the left of first defect  1020  and second defect  1030 . No shadow is produced by image  1010  since it is flat on physical medium  222 .  
         [0050]    Referring next to FIG. 12, an illustration of the shadows of the defects isolated from the image in the creation of a defect map according to one embodiment of the present invention is discussed. The results of the image captures of physical medium  222  (FIG. 2) in a first orientation and a second orientation in FIGS. 10 and 11 are combined and processed by image processing system  100  according to a method detailed in at least one embodiment of the present invention. The results isolate the defects ( 1210 ,  1220 ) into defect map  1200  that can be used to identify and correct defects in image  1010  according to at least one embodiment of the present invention.  
         [0051]    Referring to FIG. 13, a spatial histogram showing digital data captured in response to the illumination of physical medium  222  (FIG. 2) in a first orientation is discussed according to one embodiment of the present invention. The histogram is plotted by pixel amplitude and by pixel position. Image data  1310  is shown as the data with amplitudes in the range of 80 to 125 for pixel positions  400  through approximately  425 . Data for defect  1020  is shown as the pixel positions by approximately  435  to nearly  490  which shows an amplitude dropped in value from pixel position  450  to pixel position  468 . This represents shadow  1040  which falls to the right of the defect. Shadow  1040  is typically caused when light is reflected before reaching part of an image, or is blocked before it reaches part of an image, such that the amplitude of light from a portion of the image is reduced. After position  468 , the amplitude of light rises until it reaches the level of the image data again around position  480 . Therefore, a right boundary  1320  for defect  1020  can be established at position  455  based on the position of shadow  1040 .  
         [0052]    [0052]FIG. 14 illustrates the data record response of physical medium  222  (FIG. 2) in a second orientation different from the first orientation of FIG. 13 by 180°. The histogram shows a reverse pattern than from the pattern shown in the previous histogram in FIG. 13. Image data  1410  is shown with an amplitude between 80 and 125 at pixel values  470  to around  500 . The drop in amplitude for pixel positions after  445  to nearly pixel position  220  at pixel position  432  represents shadow  1110  falling to the left of the image cast again from defect  1020 . After position  432 , the amplitude rises into each level of the image data set around pixel position  420 . Thus, a left boundary  1420  for defect  1020  can be established at substantially position  445  based on the shadow position.  
         [0053]    It should be noted, with respect to FIGS. 13 and 14, that pixel intensity values that allow the creation of such histograms will be obtained for each of the colors scanned with respect to the same group of pixels. The data representing red, green, and blue, as described previously, can be used in a variety of ways, such as individually (only one of red, green, and blue from the second image used), combined together, or in dependence upon other characteristics of the image portion being scanned, such as using only red and blue in the green portion of the image and only red and green in the blue portion of the image for the purpose of creating defect map  1200  (FIG. 12).  
         [0054]    The method of the present invention records multiple orientations of a physical image, and combines these captured images to detect and correct defects in the physical medium and create a resulting captured image having improved quality. This captured image is preferably an electronic representation of the physical image, and may be stored as a digital file embodied in a computer readable medium. The captured image contained in the digital file can then be extracted from the computer readable medium and reproduced using a suitable image output device.  
         [0055]    In the preceding detailed description, reference has been made to the accompanying drawings which form a part hereof, and in which are shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical, chemical and electrical changes may be made without departing from the spirit or scope of the invention. To avoid detail not necessary to enable those skilled in the art to practice the invention, the description omits certain information known to those skilled in the art.  
         [0056]    One of the preferred implementations of the invention is as sets of instructions resident in the random access memory  115  of one or more processing systems  190  configured generally as described in FIGS.  1 - 8 . Until required by processing system  190 , the set of instructions may be stored in another computer readable memory, for example, in a hard disk drive or in a removable memory such as an optical disk for eventual use in a CD drive or DVD drive or a floppy disk for eventual use in a floppy disk drive. Further, the set of instructions can be stored in the memory of another image processing system and transmitted over a local area network or a wide area network, such as the Internet, where the transmitted signal could be a signal propagated through a medium such as an ISDN line, or the signal may be propagated through an air medium and received by a local satellite to be transferred to processing system  190 . Such a signal may be a composite signal comprising a carrier signal, and contained within the carrier signal is the desired information containing at least one computer program instruction implementing the invention, and may be downloaded as such when desired by the user. One skilled in the art would appreciate that the physical storage and/or transfer of the sets of instructions physically changes the medium upon which it is stored electrically, magnetically, or chemically so that the medium carries computer readable information. The preceding detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.