Abstract:
A method of recording a color image on a monochrome photographic recording medium by the steps of separating the color image into three color components, one luminance component and two chrominance components; and recording the three color components on adjacent areas of the recording medium, the luminance component being recorded on a larger area than either of the two chrominance components.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to a method of recording and storing color image information in a human readable fashion onto archival monochrome film for more convenient retrieval with either analog or digital techniques. 
     BACKGROUND OF THE INVENTION 
     Properly processed and stored, monochrome (e.g. Black and White silver halide) film continues to meet both legal and archival standards for the long term storage of information. This has in fact buoyed its continued use despite competition from digital imaging technologies such as magnetic and optical storage over the last decade. It is clear that monochrome silver halide film will continue to serve a vital role in the archival storage of information. Its human readable form is especially important in its acceptance since it immunizes it against digital format obsolescence which threatens to be the bane of digital storage techniques. 
     However, because monochrome film only yields monochromatic information on output, typical single channel recording methods lose all color information content of the original document. This problem is easily, but inconveniently, solved in the existing art with monochrome films by resorting to classical three channel separation techniques. This involves the recording of the original image onto monochrome film through three separate color filters, nominally red(R), green(G) and blue(B), thus arriving at three distinct and disjoined image frames or field-of-views (FOV); one for each color. For example, see U.S. Pat. No. 3,589,811 issued Jun. 29, 1971 which discloses the use of crossed beam splitters in a camera for recording three color separation images on a monochrome film. 
     A reconstructed image with color information can then be retrieved from these three records by reversing the process, with special attention paid to spatial registration of the records. Because each frame is separate and disjoined from members of its triad, the reconstruction process can become cumbersome due to handling and alignment issues. 
     U.S. Pat. No. 4,926,250 issued May 15, 1990 to Konishi discloses a color image recording and reproducing apparatus using monochromatic recording medium. The separate frames are optically recorded on microfilm and a blip mark adjacent each frame is recorded to indicate the color of the separation. The blip marks are employed in reproduction apparatus to select the color of the toner or paper, but no attempt is made to register multiple color separations in the output apparatus. 
     Existing film scanning apparatus is configured to scan a single image in a single optical field of view (FOV). The necessity of scanning three color separations to reproduce a color image recorded on a monochromatic film in the conventional manner reduces the productivity of such scanning apparatus by a factor of three. 
     It is also well known in the art that there is less visible information in the red and blue separations than in the green separation. Thus, a method that employs the same amount of recording medium for the red, blue and green separations is inefficient. 
     There exists a need therefore for an improved method of recording a color image on a monochromatic recording medium. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a spatial formatting method allowing for the convenient and efficient storage, retrieval, and reconstruction of color separation information within a single optical field-of-view (FOV) is claimed. It does so by adjoining color records within a constrained and standardized two-dimensional spatial format, with the luminance record occupying a larger portion of the FOV than the chrominance portions of the image. The method of the present invention offers the advantage of unifying color records into any single standardized FOV, and providing greater storage efficiency through use of low resolution non-luminance records. In particular, the invention provides a method of recording a color image on a monochrome photographic recording medium by the steps of separating the color image into three color components, one luminance component and two chrominance components; and recording the three color components on adjacent areas of the recording medium within a standard image format, the luminance component being recorded on a larger area than either of the two chrominance components. 
     The advantage of this form of storage is its human readability and archival legality. Since most film scanning hardware is designed to accommodate standardized formats within a single FOV, efficiency is increased by retrieving all color separation information in a single scan. 
     Parenthetically, it can be noted that the green record of the red-green-blue color separation triad is most important of the three for both tone reproduction and spatial resolution. This is largely due to its strong correlation with luminance. It is in fact well accepted in the art that the non-luminance red and blue records can generally be of half the spatial resolution of the green record yielding an imperceptible loss in image quality upon color reconstruction compared to equal spatial resolution in all three channels. 
     These and other aspects, objects, features and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic block diagram of an image processing system suitable for practicing the present invention; 
     FIG. 2 is a plan view of a recording medium bearing a color image recorded according to the present invention; 
     FIG. 3 is a flow chart showing the image processing steps performed by the image processing electronics; 
     FIG. 4 is a schematic diagram illustrating an alternative apparatus for optically recording a color image on monochromatic film according to the present invention; and 
     FIG. 5 is a schematic diagram of a color image reproduction system employing a monochromatic film image according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An example of a system for recording a color image on a monochrome film according to the present invention is shown in FIG. 1. The system generally designated 10 includes a scanner 12 for scanning an original color image 14 to produce a color digital image signal R,G,B. The original color image 14 may comprise an original scene, a color image on color photographic film or paper, or a color image generated by a computer. The scanner may comprise, for example a digital color camera, a color scanner, or other such digital color image capture device. 
     The color digital image is processed in image processing electronics 16, such as a personal computer or special purpose digital signal processing hardware, to produce a digital image file for printing the color digital image onto monochrome film 18 in a film writer 20. As shown in FIG. 2, the image written onto the film 18 by film writer 20 includes a luminance subsection 22 and a pair of chrominance subsections 24 and 26, all within a standard image format. For example, the image format may be a standard 35 mm rectangular format of 24 mm×35 mm, wherein the luminance subsection 22 occupies a 24 mm×16.5 mm area, and the two chrominance subsections 24 and 26 occupy contiguous 17.5 mm×12 mm areas. With these dimensions, a 1 mm strip 28 is left along one edge of the standard 35 mm FOV. The luminance subsection may represent, for example, a green color component and the chrominance components may represent red and blue respectively. Though the red, green, and blue records are considered nominal separation standards for storage of color information, other similar standards such as Ycc, Lab, or Luv can also be stored in a similar fashion as in FIG. 1. The luminance information (Y, L, and L respectively) of each would be recorded at full resolution while the chroma information (cc, ab, and uv) would be recorded similar to red and blue at a reduced resolution. 
     This example also shows the reduced resolution channels for non-luminance color information, red and blue in this case. Retrieval via digital electronic scanners is preferred because of the added flexibility afforded by digital data for the geometric operations such as rotation, shift, and scaling required for image registration. However, this format does not preclude the use of purely optical retrieval methods which can perform these same operations albeit in a less accurate fashion. Fiducial marks 30 may be provided at the periphery of the subsections of the image to aid in recovery of the color records in a digital scanner. 
     Referring now to FIG. 3, the steps performed by the image processing electronics 16 will be described. First, the digital image is separated (32) into color components. This may simply involve separating the red, green and blue color records if the scanner output was an R,G,B color signal, or it may involve a color space transformation to another desired color space such as Luv, Lab or YCC as is well known in the prior art. 
     Next, the color separations are sized (34) to fit into the standard format. This step may involve decimation and interpolation as is well known in the prior art. The sized color separations are then formatted (36) into a single image by rotating and arranging them in the orientation in which they will appear in the standard frame. Fiducial marks and or a filler strip 28 including image related information may be added to the digital image at this time. To insure proper tone reproduction upon retrieval and reconstruction, a stepped gray scale may be included in the filler strip 28. Finally, the digital image is sent (38) to the film writer 20, where it is recorded on the film 18. 
     As shown in FIG. 4, when the original image is a color photographic film 14, the monochrome image according to the present invention may be produced by optical recording techniques rather than digital image processing. The optical recording apparatus 40, resembling a standard photographic printer, would include a light source 42, a shutter 43, a film gate 44 for holding the film 14, a lens and filter housing 46 containing appropriate color filters, prisms, and lenses having magnification ratios to produce the monochrome image, and a film gate 48 for holding the monochrome film 18. A mask (not shown) may be provided for producing the several fiducial marks superimposed at the recording stage to allow for easy registration upon retrieval and reconstruction. 
     By far, the preferred retrieval approach for subsequent reconstruction lies in electronically scanning the color separations in their adjoined arrangement and reconstructing the image digitally. As shown in FIG. 5, this is done with a single scan in a monochrome scanner 50 covering the standardized image frame containing all three adjoined separations. 
     With a priori knowledge of the format, the digital image processing electronics 52 reverses the capture process by segmenting the image into its color separations using pattern recognition to recognize the fiducial marks, removing the fiducial marks and the image related information in the strip 28, rotating and resizing the separations, and combining the separations into one color digital image file suitable for printing on a printer 54 such as a thermal, ink jet, electrophotograhic or digital silver halide printer. 
     The invention has been described with reference to a preferred embodiment. However, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     PARTS LIST 
     10 system for recording color images on monochromatic film 
     12 scanner 
     14 original color image 
     16 image processing electronics 
     18 monochrome film 
     20 film writer 
     22 luminance subsection 
     24 chrominance subsection 
     26 chrominance subsection 
     28 filler strip 
     30 fiducial marks 
     32 separate color components step 
     34 size color separations step 
     36 format color separations step 
     38 print step 
     40 optical recording apparatus 
     42 light source 
     43 shutter 
     44 film gate 
     46 filter housing 
     48 film gate 
     50 scanner 
     52 image processing electronics 
     54 printer