Abstract:
A method of sharpening a full-color image of a scene includes capturing an image of the scene using a two-dimensional sensor array having both color and panchromatic pixels; forming the full-color image in response to the captured color pixels and forming a reference panchromatic image in response to the captured panchromatic pixels; forming a high-frequency panchromatic image from the reference panchromatic image; and providing a sharpened full-color image in response to the high-frequency panchromatic image and the full-color image.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     Reference is made to commonly assigned U.S. patent application Ser. No. 11/341,206, filed Jan. 27, 2006 by James E. Adams, Jr. et al, entitled “Interpolation of Panchromatic and Color Pixels”, and U.S. patent application Ser. No. 11/565,451, filed Nov. 29, 2006 by James E. Adams, Jr. et al, entitled “Providing a Desired Resolution Color Image”, the disclosures of which are incorporated herein. 
     FIELD OF THE INVENTION 
     The present invention relates to forming a color image having a desired sharpness from a panchromatic image and a color image having less than the desired sharpness. 
     BACKGROUND OF THE INVENTION 
     Video cameras and digital still cameras generally employ a single image sensor with a color filter array to record a scene. This approach begins with a sparsely populated single-channel image in which the color information is encoded by the color filter array pattern. Subsequent interpolation of the neighboring pixel values permits the reconstruction of a complete three-channel, full-color image. This full-color image, in turn, can be sharpened to improve the appearance of sharp edges and fine detail. One popular approach is to either directly detect or synthesize a luminance color channel, e.g. “green”, and then to generate a high-frequency luminance image as an initial step. This high-frequency luminance channel is then modified in a variety of ways and then added to the full-color image to produce a sharpened full-color image. One typical example is taught in U.S. Pat. No. 5,237,402 (Deshon et al.) in which the full-color image is converted into a luminance-chrominance space and a high-frequency luminance image is generated from the luminance channel and then added back to the full-color image after color correction and conversion back to the original color space. A method of high-frequency luminance image modification based on adaptive amplification of the high-frequency luminance values is disclosed in U.S. Pat. No. 5,038,388 (Song). 
     In the instance of remote sensing (satellite imagery), it is advantageous from a signal-to-noise perspective to directly sense a panchromatic channel using scanning optical system. This panchromatic channel can then be used in place of a luminance channel in the sharpening process. U.S. Pat. No. 5,949,914 (Yuen) describes directly sensing a higher-resolution panchromatic image and several lower-resolution narrow-band color images, and performing an iterative deconvolution process responsive to the panchromatic image to sharpen the narrow-band color images. U.S. Pat. No. 6,097,835 (Lindgren) teaches a method of projecting the directly sensed, higher resolution panchromatic image onto the lower narrow-band color images to extract the appropriate sharpening image components that are subsequently used to sharpen the narrow-band color images. The direct implementation of these methods in video and digital still cameras is hampered by the inability to incorporate similar scanning optical system within said cameras. 
     Under low-light imaging situations, it is advantageous to have one or more of the pixels in the color filter array unfiltered, i.e. white or panchromatic in spectral sensitivity. These panchromatic pixels have the highest light sensitivity capability of the capture system. Employing panchromatic pixels represents a tradeoff in the capture system between light sensitivity and color spatial resolution. To this end, many four-color color filter array systems have been described. U.S. Pat. No. 6,529,239 (Dyck et al.) teaches a green-cyan-yellow-white pattern that is arranged as a 2×2 block that is tessellated over the surface of the sensor. U.S. Pat. No. 6,757,012 (Hubina et al.) discloses both a red-green-blue-white pattern and a yellow-cyan-magenta-white pattern. In both cases, the colors are arranged in a 2×2 block that is tessellated over the surface of the imager. The difficulty with such systems is that only one-quarter of the pixels in the color filter array have highest light sensitivity, thus limiting the overall low-light performance of the capture device. 
     To address the need of having more pixels with highest light sensitivity in the color filter array, U.S. patent application Publication No. 2003/0210332 (Frame) describes a pixel array with most of the pixels being unfiltered. Relatively few pixels are devoted to capturing color information from the scene producing a system with low color spatial resolution capability. Additionally, Frame teaches using simple linear interpolation techniques that are not responsive to or protective of high frequency color spatial details in the image. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to produce a digital color image having the desired sharpness from a digital image having panchromatic and color pixels. 
     This object is achieved by a method of sharpening a full-color image of a scene comprising: 
     (a) capturing an image of the scene using a two-dimensional sensor array having both color and panchromatic pixels; 
     (b) forming the full-color image in response to the captured color pixels and forming a reference panchromatic image in response to the captured panchromatic pixels; 
     (c) forming a high-frequency panchromatic image from the reference panchromatic image; and 
     (d) providing a sharpened full-color image in response to the high-frequency panchromatic image and the full-color image. 
     It is a feature of the present invention that images can be captured under low-light conditions with a sensor having panchromatic and color pixels and processing produces the desired sharpness in a digital color image produced from the panchromatic and colored pixels. 
     The present invention makes use of a color filter array with an appropriate composition of panchromatic and color pixels in order to permit the above method to provide both improved low-light sensitivity and improved color spatial resolution fidelity. The above method preserves and enhances panchromatic and color spatial details and produce a sharpened full-color image. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective of a computer system including a digital camera for implementing the present invention; 
         FIG. 2  is a block diagram of a portion of a preferred embodiment of the present invention; 
         FIG. 3  is a block diagram showing another portion of the preferred embodiment of the present invention; 
         FIG. 4  is a block diagram showing an alternate embodiment of the present invention; 
         FIG. 5  is a block diagram showing an alternate embodiment of the present invention; 
         FIG. 6  is a block diagram showing block  234  in  FIG. 5  in more detail of an alternate embodiment of the present invention; 
         FIG. 7  is a block diagram showing block  234  in  FIG. 5  in more detail of an alternate embodiment of the present invention; 
         FIG. 8  is a block diagram showing block  234  in  FIG. 5  in more detail of an alternate embodiment of the present invention; 
         FIG. 9  is a block diagram showing block  234  in  FIG. 5  in more detail of an alternate embodiment of the present invention; 
         FIG. 10A  is a block diagram showing an alternate embodiment of the present invention; 
         FIG. 10B  is a block diagram showing block  278  in  FIG. 10A  in more detail of an alternate embodiment of the present invention; 
         FIG. 11A  is a block diagram showing an alternate embodiment of the present invention; 
         FIG. 11B  is a block diagram showing block  296  in  FIG. 11A  in more detail of an alternate embodiment of the present invention; 
         FIG. 12A  is a block diagram showing an alternate embodiment of the present invention; 
         FIG. 12B  is a block diagram showing block  318  in  FIG. 12A  in more detail of an alternate embodiment of the present invention; and 
         FIG. 13  is a block diagram showing an alternate embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In the following description, a preferred embodiment of the present invention will be described in terms that would ordinarily be implemented as a software program. Those skilled in the art will readily recognize that the equivalent of such software can also be constructed in hardware. Because image manipulation algorithms and systems are well known, the present description will be directed in particular to algorithms and systems forming part of, or cooperating more directly with, the system and method in accordance with the present invention. Other aspects of such algorithms and systems, and hardware or software for producing and otherwise processing the image signals involved therewith, not specifically shown or described herein, can be selected from such systems, algorithms, components and elements known in the art. Given the system as described according to the invention in the following materials, software not specifically shown, suggested or described herein that is useful for implementation of the invention is conventional and within the ordinary skill in such arts. 
     Still further, as used herein, the computer program can be stored in a computer readable storage medium, which can include, for example; magnetic storage media such as a magnetic disk (such as a hard drive or a floppy disk) or magnetic tape; optical storage media such as an optical disc, optical tape, or machine readable bar code; solid state electronic storage devices such as random access memory (RAM), or read only memory (ROM); or any other physical device or medium employed to store a computer program. 
     Before describing the present invention, it facilitates understanding to note that the present invention is preferably utilized on any well-known computer system, such as a personal computer. Consequently, the computer system will not be discussed in detail herein. It is also instructive to note that the images are either directly input into the computer system (for example by a digital camera) or digitized before input into the computer system (for example by scanning an original, such as a silver halide film). 
     Referring to  FIG. 1 , there is illustrated a computer system  110  for implementing the present invention. Although the computer system  110  is shown for the purpose of illustrating a preferred embodiment, the present invention is not limited to the computer system  110  shown, but can be used on any electronic processing system such as found in home computers, kiosks, retail or wholesale photofinishing, or any other system for the processing of digital images. The computer system  110  includes a microprocessor-based unit  112  for receiving and processing software programs and for performing other processing functions. A display  114  is electrically connected to the microprocessor-based unit  112  for displaying user-related information associated with the software, e.g., by a graphical user interface. A keyboard  116  is also connected to the microprocessor based unit  112  for permitting a user to input information to the software. As an alternative to using the keyboard  116  for input, a mouse  118  can be used for moving a selector  120  on the display  114  and for selecting an item on which the selector  120  overlays, as is well known in the art. 
     A compact disk-read only memory (CD-ROM)  124 , which typically includes software programs, is inserted into the microprocessor based unit for providing a way of inputting the software programs and other information to the microprocessor based unit  112 . In addition, a floppy disk  126  can also include a software program, and is inserted into the microprocessor-based unit  112  for inputting the software program. The compact disk-read only memory (CD-ROM)  124  or the floppy disk  126  can alternatively be inserted into externally located disk drive unit  122  which is connected to the microprocessor-based unit  112 . Still further, the microprocessor-based unit  112  can be programmed, as is well known in the art, for storing the software program internally. The microprocessor-based unit  112  can also have a network connection  127 , such as a telephone line, to an external network, such as a local area network or the Internet. A printer  128  can also be connected to the microprocessor-based unit  112  for printing a hardcopy of the output from the computer system  110 . 
     Images can also be displayed on the display  114  via a personal computer card (PC card)  130 , such as, as it was formerly known, a PCMCIA card (based on the specifications of the Personal Computer Memory Card International Association) which contains digitized images electronically embodied in the PC card  130 . The PC card  130  is ultimately inserted into the microprocessor based unit  112  for permitting visual display of the image on the display  114 . Alternatively, the PC card  130  can be inserted into an externally located PC card reader  132  connected to the microprocessor-based unit  112 . Images can also be input via the compact disk-read only memory (CD-ROM)  124 , the floppy disk  126 , or the network connection  127 . Any images stored in the PC card  130 , the floppy disk  126  or the compact disk-read only memory (CD-ROM)  124 , or input through the network connection  127 , can have been obtained from a variety of sources, such as a digital camera (not shown) or a scanner (not shown). Images can also be input directly from a digital camera  134  via a camera docking port  136  connected to the microprocessor-based unit  112  or directly from the digital camera  134  via a cable connection  138  to the microprocessor-based unit  112  or via a wireless connection  140  to the microprocessor-based unit  112 . 
     In accordance with the invention, the algorithm can be stored in any of the storage devices heretofore mentioned and applied to images in order to sharpen the images. 
       FIG. 2  is a high-level diagram the first portion of a preferred embodiment of the present invention. The digital camera  134  is responsible for creating an original digital red-green-blue-panchromatic (RGBP) color filter array (CFA) image  200 , also referred to as the digital RGBP CFA image or the RGBP CFA image. It is noted at this point that other color channel combinations, such as cyan-magenta-yellow-panchromatic, can be used in place of red-green-blue-panchromatic in the following description. The key item is the inclusion of a panchromatic channel. This image is considered to be a sparsely sampled image because each pixel in the image contains only one pixel value of red, green, blue, or panchromatic data. A panchromatic image interpolation block  202  produces a reference panchromatic image  204  from the RGBP CFA image  200 . At this point in the image processing chain, each color pixel location has an associated panchromatic value and either a red, green, or a blue value. From the RGBP CFA image  200  and the reference panchromatic image  204 , an RGB CFA image interpolation block  206  subsequently produces a full-color image  208 . In  FIG. 2 , the panchromatic image interpolation block  202  and the RGB CFA image interpolation block  206  can be performed in any appropriate ways known to those skilled in the art. 
       FIG. 3  is a high-level diagram of the second portion of the preferred embodiment of the present invention. A high-frequency panchromatic image generation block  210  produces a high-frequency panchromatic image  212  from the reference panchromatic image  204  ( FIG. 2 ). The sharpened full-color image generation block  214  produces a sharpened full-color image  216  from the high-frequency panchromatic image  212  and the full-color image  208  ( FIG. 2 ). 
     In  FIG. 3 , the high-frequency panchromatic image generation block  210  can be performed in any appropriate way known to those skilled in the art. Two examples are given. The first example is to perform a convolution of the reference panchromatic image  204  ( FIG. 2 ) with the following high-pass convolution kernel to produce the high-frequency panchromatic image  212 : 
               1   16     ⁢     (           -   1           -   2           -   1               -   2         12         -   2               -   1           -   2           -   1           )           
The second example is to perform a convolution of the reference panchromatic image  204  ( FIG. 2 ) with the following low-pass convolution kernel to produce a low-frequency panchromatic image:
 
               1   16     ⁢     (         1       2       1           2       4       2           1       2       1         )           
The low-frequency panchromatic image is now subtracted from the reference panchromatic image  204  ( FIG. 2 ) to produce the high-frequency panchromatic image  212 .
 
     In  FIG. 3 , the sharpened full-color image generation block  214  can be performed in any appropriate way known to those skilled in the art. As an example, the high-frequency panchromatic image  212  is added to the full-color image  208  ( FIG. 2 ) to produce a sharpened full-color image  216 . 
       FIG. 4  is a high-level diagram of an alternate embodiment of the present invention. A high-frequency panchromatic image generation block  218  produces a high-frequency panchromatic image  220  from the reference panchromatic image  204  ( FIG. 2 ). A high-frequency panchromatic image modification block  222  produces a modified high-frequency panchromatic image  224  from a high-frequency panchromatic image  220 . A sharpened full-color image generation block  226  produces a sharpened full-color image  228  from the modified high-frequency panchromatic image  224  and the full-color image  208  ( FIG. 2 ). 
     In  FIG. 4 , the high-frequency panchromatic image generation block  218  can be performed in the same way as the high-frequency panchromatic image generation block  210  ( FIG. 3 ). The high-frequency panchromatic image modification block  222  can be performed in any appropriate way known to those skilled in the art. As an example, U.S. Pat. No. 6,173,085 (Hamilton, Jr. et al.) teaches the use of a coring function to modify a high-frequency image. The sharpened full-color image generation block  226  can be performed in the same way as the sharpened full-color image generation block  214  ( FIG. 3 ). 
       FIG. 5  is a high-level diagram of an alternate embodiment of the present invention. A high-frequency panchromatic image generation block  230  produces a high-frequency panchromatic image  232  from the reference panchromatic image  204  ( FIG. 2 ). A high-frequency panchromatic image modification block  234  produces a modified high-frequency panchromatic image  236  from the high-frequency panchromatic image  232  and the reference panchromatic image  204  ( FIG. 2 ). A sharpened full-color image generation block  238  produces a sharpened full-color image  240  from the modified high-frequency panchromatic image  236  and the full-color image  208  ( FIG. 2 ). 
     In  FIG. 5 , the high-frequency panchromatic image generation block  230  can be performed in the same way as the high-frequency panchromatic image generation block  210  ( FIG. 3 ). The high-frequency panchromatic image modification block  234  can be performed in any appropriate way known to those skilled in the art. Examples will be given in subsequent paragraphs. The sharpened full-color image generation block  238  can be performed in the same way as the sharpened full-color image generation block  214  ( FIG. 3 ). 
       FIG. 6  is a detailed diagram of the high-frequency panchromatic image modification block  234  ( FIG. 5 ). An edge mask generation block  242  produces an edge mask  244  from the reference panchromatic image  204  ( FIG. 2 ). A high-frequency panchromatic image scaling block  246  produces the modified high-frequency panchromatic image  236  ( FIG. 5 ) from the edge mask  244  and the high-frequency panchromatic image  212  ( FIG. 5 ). 
     In  FIG. 6 , the edge mask generation block  242  can be performed in any appropriate way known to those skilled in the art. As an example, the reference panchromatic image  204  ( FIG. 2 ) can be convolved with one or more edge detection convolution kernels and the results combined as a vector norm. Finally, a small bias value can be subtracted from the resulting vector norm to provide a noise-cleaning capability. As an explicit example: 
             M   =       k   ⁡     (            P   *     (         1       0         -   1             2       0         -   2             1       0         -   1           )            +          P   *     (         1       2       1           0       0       0             -   1           -   2           -   1           )              )       -   b           
In this equation, M is the edge mask  244 , P is the reference panchromatic image  204  ( FIG. 2 ), k is a scaling constant, and b is a predetermined bias constant. k is typically set to a value of one-eighth and can be adjusted from that point to increase or decrease the effects of the edge mask. To determine an appropriate value for b, one typically computes the edge mask with b set to zero and then computes the standard deviation of the edge mask values in a region of P known to be free of scene detail, e.g., a clear sky or a flat wall. b is then set to one or two times the standard deviation. The high-frequency panchromatic image scaling block  246  can be performed in any appropriate way known to those skilled in the art. As an example, the edge mask  244  can be multiplied with the high-frequency panchromatic image  212  ( FIG. 5 ) to produce the modified high-frequency panchromatic image  236  ( FIG. 5 ).
 
       FIG. 7  is a detailed diagram of an alternate embodiment of the high-frequency panchromatic image modification block  234  ( FIG. 5 ). An edge mask generation block  248  produces an edge mask  250  from the reference panchromatic image  204  ( FIG. 2 ). A high-frequency panchromatic image scaling block  252  produces a scaled high-frequency panchromatic image  254  from the edge mask  250  and the high-frequency panchromatic image  212  ( FIG. 5 ). A coring block  256  produces the modified high-frequency panchromatic image  236  ( FIG. 5 ) from the scaled high-frequency panchromatic image  254 . 
     In  FIG. 7 , the edge mask generation block  248  can be performed in the same way as the edge mask generation block  242  ( FIG. 6 ). The high-frequency panchromatic image scaling block  252  can be performed in the same way as the high-frequency panchromatic image scaling block  246  ( FIG. 6 ). The coring block  256  can be performed as in the aforementioned reference U.S. Pat. No. 6,173,085 (Hamilton, Jr. et al.) 
       FIG. 8  is a detailed diagram of an alternate embodiment of the high-frequency panchromatic image modification block  234  ( FIG. 5 ). An edge mask generation block  258  produces an edge mask  260  from the reference panchromatic image  204  ( FIG. 2 ). A coring block  262  produces a cored edge mask  264  from the edge mask  260 . A high-frequency panchromatic image scaling block  266  produces the modified high-frequency panchromatic image  236  ( FIG. 5 ) from the cored edge mask  264  and the high-frequency panchromatic image  212  ( FIG. 5 ). 
     In  FIG. 8 , the edge mask generation block  258  can be performed in the same way as the edge mask generation block  242  ( FIG. 6 ). The coring block  262  can be performed in the same way as the coring block  256  ( FIG. 7 ). The high-frequency panchromatic image scaling block  266  can be performed in the same way as the high-frequency panchromatic image scaling block  246  ( FIG. 6 ). 
       FIG. 9  is a detailed diagram of an alternate embodiment of the high-frequency panchromatic image modification block  234  ( FIG. 5 ). An edge mask generation block  268  produces an edge mask  270  from the reference panchromatic image  204  ( FIG. 2 ). A coring block  274  produces a cored high-frequency panchromatic image  276  from the high-frequency panchromatic image  212  ( FIG. 5 ). A high-frequency panchromatic image scaling block  272  produces the modified high-frequency panchromatic image  236  ( FIG. 5 ) from the edge mask  270  and the cored high-frequency panchromatic image  276 . 
     In  FIG. 9 , the edge mask generation block  268  can be performed in the same way as the edge mask generation block  242  ( FIG. 6 ). The coring block  274  can be performed in the same way as the coring block  256  ( FIG. 7 ). The high-frequency panchromatic image scaling block  272  can be performed in the same way as the high-frequency panchromatic image scaling block  246  ( FIG. 6 ). 
       FIG. 10A  is a high-level diagram of an alternate embodiment of the present invention. A modify reference panchromatic image block  278  produces a modified reference panchromatic image  280  from the reference panchromatic image  204  ( FIG. 2 ). It will be clear to those skilled in the art that the modified reference panchromatic image  280  can be used in place of the reference panchromatic image  204  ( FIG. 2 ) in any of the previously or subsequently described embodiments of the present invention. 
       FIG. 10B  is a detailed diagram of the modify reference panchromatic image block  278  ( FIG. 10A ). A compute high-frequency panchromatic image block  282  produces a high-frequency panchromatic image  284  from the reference panchromatic image  204  ( FIG. 2 ). A coring block  286  produces a cored high-frequency panchromatic image  292  from the high-frequency panchromatic image  284 . A compute low-frequency panchromatic image block  288  produces a low-frequency panchromatic image  290  from the reference panchromatic image  204  ( FIG. 2 ). The generate modified reference panchromatic image block  294  produces the modified reference panchromatic image  280  ( FIG. 10A ) from the cored high-frequency panchromatic image  292  and the low-frequency panchromatic image  290 . 
     In  FIG. 10B , the compute high-frequency panchromatic image block  282  can be performed in the same way as the high-frequency panchromatic image generation block  210  ( FIG. 3 ). The coring block  286  can be performed in the same way as the coring block  256  ( FIG. 7 ). The compute low-frequency panchromatic image block  288  can be performed in any appropriate way known to those skilled in the art. As an example, the high-frequency panchromatic image  284  can be subtracted from the reference panchromatic image  204  ( FIG. 2 ) to produce the low-frequency panchromatic image  290 . A generate modified reference panchromatic image block  294  can be performed in any appropriate way known to those skilled in the art. As an example, the cored high-frequency panchromatic image  292  can be added to the low-frequency panchromatic image  290  to produce the modified reference panchromatic image  280  ( FIG. 10A ). 
       FIG. 11A  is a high-level diagram of an alternate embodiment of the present invention. A modify reference panchromatic image block  296  produces a modified reference panchromatic image  298  from the reference panchromatic image  204  ( FIG. 2 ). It will be clear to those skilled in the art that the modified reference panchromatic image  298  can be used in place of the reference panchromatic image  204  ( FIG. 2 ) in any of the previously or subsequently described embodiments of the present invention. 
       FIG. 11B  is a detailed diagram of the modify reference panchromatic image block  296  ( FIG. 11A ). A compute low-frequency panchromatic image block  300  produces a low-frequency panchromatic image  302  from the reference panchromatic image  204  ( FIG. 2 ) and a high-frequency panchromatic image  308 . A compute high-frequency panchromatic image block  306  produces a high-frequency panchromatic image  308  from the reference panchromatic image  204  ( FIG. 2 ). A generate edge mask block  312  produces an edge mask  314  from the reference panchromatic image  204  ( FIG. 2 ). A mask high-frequency panchromatic image block  310  produces a masked high-frequency panchromatic image  316  from the high-frequency panchromatic image  308  and the edge mask  314 . A generate modified reference panchromatic image block  304  produces the modified reference panchromatic image  298  ( FIG. 11A ) from the masked high-frequency panchromatic image  316  and the low-frequency panchromatic image  302 . 
     In  FIG. 11B , the compute low-frequency panchromatic image block  300  can be performed in the same way as the compute low-frequency panchromatic image block  288  ( FIG. 10B ). The compute high-frequency panchromatic image block  306  can be performed in the same way as the high-frequency panchromatic image generation block  210  ( FIG. 3 ). The generate edge mask block  312  can be performed in the same way as the edge mask generation block  242  ( FIG. 6 ). The mask high-frequency panchromatic image block  310  can be performed in the same way as the high-frequency panchromatic image scaling block  246  ( FIG. 6 ). The generate modified reference panchromatic image block  304  can be performed in the same way as the generate modified reference panchromatic image block  294  ( FIG. 10B ). 
       FIG. 12A  is a high-level diagram of an alternate embodiment of the present invention. A modify reference panchromatic image block  318  produces a modified reference panchromatic image  320  from the reference panchromatic image  204  ( FIG. 2 ). It will be clear to those skilled in the art that the modified reference panchromatic image  320  can be used in place of the reference panchromatic image  204  ( FIG. 2 ) in any of the previously or subsequently described embodiments of the present invention. 
       FIG. 12B  is a detailed diagram of the modify reference panchromatic image block  318  ( FIG. 12A ). A photometric space conversion block  322  produces a modified reference panchromatic image  320  ( FIG. 12A ) from the reference panchromatic image  204  ( FIG. 2 ). The photometric space conversion block  322  can be performed in any appropriate way known to those skilled in the art. As an example, U.S. Pat. No. 5,708,729 (Adams et al.) teaches the use of a logarithm and polynomial function to photometrically convert an image. 
       FIG. 13  is a high-level diagram of an alternate embodiment of the present invention. The modify reference panchromatic image block  278  ( FIG. 10A ) produces a modified reference panchromatic image  324  from the reference panchromatic image  204  ( FIG. 2 ). The modify reference panchromatic image  296  ( FIG. 11A ) produces a modified reference panchromatic image  326  from the modified reference panchromatic image  324 . The modify reference panchromatic image  318  ( FIG. 12A ) produces a modified reference panchromatic image  328  from the modified reference panchromatic image  326 . It will be clear to those skilled in the art that the chain of operations shown in  FIG. 13  can be lengthened, shortened, and rearranged in any manner and remain within the spirit and scope of the invention. 
     The sharpening algorithms disclosed in the preferred embodiments of the present invention can be employed in a variety of user contexts and environments. Exemplary contexts and environments include, without limitation, wholesale digital photofinishing (which involves exemplary process steps or stages such as film in, digital processing, prints out), retail digital photofinishing (film in, digital processing, prints out), home printing (home scanned film or digital images, digital processing, prints out), desktop software (software that applies algorithms to digital prints to make them better or even just to change them), digital fulfillment (digital images in—from media or over the web, digital processing, with images out—in digital form on media, digital form over the web, or printed on hard-copy prints), kiosks (digital or scanned input, digital processing, digital or scanned output), mobile devices (e.g., PDA or cell phone that can be used as a processing unit, a display unit, or a unit to give processing instructions), and as a service offered via the World Wide Web. 
     In each case, the sharpening algorithms can stand alone or can be a component of a larger system solution. Furthermore, the interfaces with the algorithm, e.g., the scanning or input, the digital processing, the display to a user (if needed), the input of user requests or processing instructions (if needed), the output, can each be on the same or different devices and physical locations, and communication between the devices and locations can be via public or private network connections, or media based communication. Where consistent with the foregoing disclosure of the present invention, the algorithms themselves can be fully automatic, can have user input (be fully or partially manual), can have user or operator review to accept/reject the result, or can be assisted by metadata (metadata that can be user supplied, supplied by a measuring device (e.g. in a camera), or determined by an algorithm). Moreover, the algorithms can interface with a variety of workflow user interface schemes. 
     The sharpening algorithms disclosed herein in accordance with the invention can have interior components that utilize various data detection and reduction techniques (e.g., face detection, eye detection, skin detection, flash detection). 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           110  Computer System 
           112  Microprocessor-based Unit 
           114  Display 
           116  Keyboard 
           118  Mouse 
           120  Selector on Display 
           122  Disk Drive Unit 
           124  Compact Disk—read Only Memory (CD-ROM) 
           126  Floppy Disk 
           127  Network Connection 
           128  Printer 
           130  Personal Computer Card (PC card) 
           132  PC Card Reader 
           134  Digital Camera 
           136  Camera Docking Port 
           138  Cable Connection 
           140  Wireless Connection 
           200  RGBP CFA Image 
           202  Panchromatic Image Interpolation 
           204  Reference Panchromatic Image 
           206  RGB CFA Image Interpolation 
           208  Full-Color Image 
           210  High-Frequency Panchromatic Image Generation 
           212  High-Frequency Panchromatic Image 
           214  Sharpened Full-Color Image Generation 
           216  Sharpened Full-Color Image 
           218  High-Frequency Panchromatic Image Generation 
           220  High-Frequency Panchromatic Image 
           222  High-Frequency Panchromatic Image Modification 
           224  Modified High-Frequency Panchromatic Image 
           226  Sharpened Full-Color Image Generation 
           228  Sharpened Full-Color Image 
           230  High-Frequency Panchromatic Image Generation 
           232  High-Frequency Panchromatic Image 
           234  High-Frequency Panchromatic Image Modification 
           236  Modified High-Frequency Panchromatic Image 
           238  Sharpened Full-Color Image Generation 
           240  Sharpened Full-Color Image 
           242  Edge Mask Generation 
           244  Edge Mask 
           246  High-Frequency Panchromatic Image Scaling 
           248  Edge Mask Generation 
           250  Edge Mask 
           252  High-Frequency Panchromatic Image Scaling 
           254  Scaled High-Frequency Panchromatic Image 
           256  Coring 
           258  Edge Mask Generation 
           260  Edge Mask 
           262  Coring 
           264  Cored Edge Mask 
           266  High-Frequency Panchromatic Image Scaling 
           268  Edge Mask Generation 
           270  Edge Mask 
           272  High-Frequency Panchromatic Image Scaling 
           274  Coring 
           276  Cored High-Frequency Panchromatic Image 
           278  Modify Reference Panchromatic Image 
           280  Modified Reference Panchromatic Image 
           282  Compute High-Frequency Panchromatic Image 
           284  High-Frequency Panchromatic Image 
           286  Coring 
           288  Compute Low-Frequency Panchromatic Image 
           290  Low-Frequency Panchromatic Image 
           292  Cored High-Frequency Panchromatic Image 
           294  Generate Modified Reference Panchromatic Image 
           296  Modify Reference Panchromatic Image 
           298  Modified Reference Panchromatic Image 
           300  Compute Low-Frequency Panchromatic Image 
           302  Low-Frequency Panchromatic Image 
           304  Generate Modified Reference Panchromatic Image 
           306  Compute High-Frequency Panchromatic Image 
           308  High-Frequency Panchromatic Image 
           310  Mask High-Frequency Panchromatic Image 
           312  Generate Edge Mask 
           314  Edge Mask 
           316  Masked High-Frequency Panchromatic Image 
           318  Modify Reference Panchromatic Image 
           320  Modified Reference Panchromatic Image 
           322  Photometric Space Conversion 
           324  Modified Reference Panchromatic Image 
           326  Modified Reference Panchromatic Image 
           328  Modified Reference Panchromatic Image