Computer graphics processing and selective visual display system – Computer graphics processing – Attributes
Reexamination Certificate
1998-07-10
2002-04-02
Luu, Matthew (Department: 2779)
Computer graphics processing and selective visual display system
Computer graphics processing
Attributes
C345S600000
Reexamination Certificate
active
06366291
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of converting colorimetric values to display signals input into a color display device and a technique of inversely converting the display signals to the colorimetric values.
2. Description of the Related Art
A conventional technique reads an original color image, for example, from a color film, color photographic paper, or a color print, with a color scanner, obtains three color signals of R (red), G (green), and B (blue) corresponding to the input original color image, and gives the obtained RGB color signals to a color monitor to display a color image in an interactive manner for the purpose of checking the input color image or carrying out the required processing.
The RGB color signals read with the color scanner depend upon only the characteristics of a color separation filter of the color scanner. Transmission of the RGB color signals to the color monitor without any processing accordingly does not give a color image that is sufficiently close to the original color image.
In the field of image processing for prints and newspapers, four color inks C (cyan), M (magenta), Y (yellow), and K(black) are used for color printing. Each pixel of an original image for color printing is subjected to color conversion and consists of four color signals of C, M, Y, and K. In the intermediate stage of image processing, in order to preview an image being processed or an expected final image, the CMYK color signals for color printing are converted into the RGB color signals and given to the color monitor for display of a color image.
Simple conversion of the CMYK color signals for color printing to the RGB color signals and transmission of the converted RGB color signals to the color monitor, however, does not give a color image that is sufficiently close to an actual color printed image.
The RGB color signals depending upon only the characteristics of the color separation filter or the CMYK color signals for color printing should be subjected to color conversion to RGB color signals for a target color monitor. Such conversion process enables a desired color image to be displayed on the color monitor.
The color monitor can display only the colors included in a color range defined by fluorescent materials of three colors, red, green, and blue (that is, in the gamut intrinsic to the color monitor), whereas the gamut of an original color image or the gamut of a color printed image often includes colors that are located out of the color range defined by the fluorescent materials of three colors (red, green, and blue) of the color monitor.
When the values of the RGB color signals for the color monitor obtained by the color conversion are normalized in the range of 0 to 1, at least one signal out of the RGB color signals for the color monitor has a value of less than 0 (that is, a negative value) or a value of greater than 1 (that is, a value exceeding 100%), with respect to the colors located out of the color range defined by the fluorescent materials of three colors (red, green, and blue) of the color monitor.
Normalization of the values of the RGB color signals for the color monitor in the range of 0 to 1 implies that the values of the RGB color signals required for expression of white on the color monitor are respectively set equal to 1 (that is, the maximum value) and that the values of the RGB color signals required for expression of black on the color monitor are respectively set equal to 0 (that is, the minimum value). The fluorescent material can not accordingly emit at the values of greater than 1 or at the values of less than 0.
In such cases, the conventional technique limits the values of the RGB color signals for the color monitor to the maximum value ‘1’ or the minimum value ‘0’ even when the values of greater than 1 or the values of less than 0 are required as the values of the RGB color signals for the color monitor.
In case that a desired color included in an original color image or a color printed image is out of the color range reproducible by the fluorescent materials of the color monitor, the values of the RGB color signals for the color monitor are uniformly limited to the maximum value ‘1’ or the minimum value ‘0’ with respect to the desired color (for example, the color of high saturation). This arises a significant problem of abnormal tone in an area of the desired color.
In case that a desired color included in an original color image or a color printed image exists over the border of the inside and the outside of the color range reproducible by the fluorescent materials of the color monitor, all the values of the three color signals RGB are not uniformly limited to the maximum value ‘1’ or the minimum value ‘0’ on the border of the color range. Only the value of the color signal that is greater than the maximum ‘1’ or is less than the minimum ‘0’ is limited to the maximum value ‘1’ or the minimum value ‘0’, while the values of the other color signals continue variation. This causes the hue to abruptly change in the vicinity of the border of the color range.
The area of colors of high saturation is generally prominent in an image. The abnormal tone or the change in hue in such prominent areas often lead to a critical problem.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a method of and an apparatus for color conversion, which effectively prevents abnormal tone or a change in hue in an area of a desired color that exists out of a reproducible color range.
At least part of the above and the other related objects is realized by a first method of color conversion, which converts colorimetric values of a composite color into mixing quantities of device primary colors in additive color mixture according to a first conversion relation and subsequently converts the mixing quantities of the device primary colors into intensities of display signals according to a second conversion relation, respectively. A relievable area that is out of and adjacent to a reproducible range and within a predetermined maximum relievable range is determined for at least one selected device primary color among the device primary colors as a function of the mixing quantities of the remaining device primary colors other than the selected device primary. When the mixing quantity of the selected device primary color is within the reproducible range, the mixing quantity of the selected device primary color is converted into the intensity of the display signal within the first conversion range preset in a definition range. When the mixing quantity of the selected device primary color is within the relievable range, on the other hand, the mixing quantity of the selected device primary color is converted into the intensity of the display signal within the second conversion range other than the first conversion range in the definition range.
The present invention is also directed to a first color conversion apparatus which converts colorimetric values representing a composite color into display signals that are to be input into a target color display device to reproduce the composite color, the display signals being related to mixing quantities of device primary colors in additive color mixture, the device primary colors being single-color components reproduced by respective single-color elements of the target color display device, the composite color being reproduced by the target color display device as a mixture of the device primary colors mixed by respective mixing quantities responsive to the display signals, the target color display device having a reproducible range of the mixing quantity for each of the device primary colors.
The first color conversion apparatus includes: means for defining a definition range of intensities of the display signals, wherein those display signals whose intensities are within the definition range are to be converted in the target color display device to the mixture quantities within the reproducible range, the definition range being div
Narazaki Makoto
Sakamoto Takashi
Taniguchi Kazutaka
Dainippon Screen Mfg. Co,. Ltd.
Harrison Chant′
Luu Matthew
Ostrolenk Faber Gerb & Soffen, LLP
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