Color image processing method and apparatus therefor
AssigneeCanon Kabushiki Kaisha
InventorsKen-ichi Ohta, Akihiro Usami
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Abstract
A color-image processing method and apparatus for transforming color-separated RGB image signals into CMY color signals, extracting a minimum-value signal K based upon each of the CMY signals, subjecting each of the CMY signals and the minimum-value signal K to matrix transformation in accordance with prescribed transformation coefficients and outputting the transformed signals, whereby the RGB image signals can be transformed into CMYK color signals efficiently without sacrificing color reproducibility.
Claims11
A color image processing apparatus in which first color-separated image signals, which represent a color, are converted to second color-separated image signals and a black signal, which together represent the same color, said color image processing apparatus comprising:
- input means for inputting first color-separated image signals and a minimum-value signal extracted from the first color-separated image signals;
- calculating means for (i) performing a matrix calculation on both the first color-separated image signals and the minimum-value signal, the matrix calculation using prescribed correction coefficients, and (ii) obtaining second color-separated image signals and a black signal;
- and
- output means for outputting the second color-separated image signals and the black signal obtained by said calculating means,
- wherein the prescribed correction coefficients are set so that the second color-separated image signals obtained by said calculating means are substantially 0 when the color represented by the first color-separated image signals is an achromatic color.
A color image processing method in which first color-separated image signals, which represent a color, are converted to second color-separated image signals and a black signal, which together represent the same color, said color image processing method comprising the steps of:
- inputting first color-separated image signals and a minimum-value signal extracted from the first color-separated image signals;
- performing a matrix calculation on both the first color-separated image signals and the minimum-value signal, the matrix calculation using prescribed correction coefficients, and obtaining second color-separated image signals and a black signal;
- and
- outputting the second color-separated image signals and the black signal obtained by the matrix calculation,
- wherein the prescribed correction coefficients are set so that the second color-separated image signals obtained by the matrix calculation are substantially 0 when the color represented by the first color-separated image signals is an achromatic color.
A color image processing apparatus in which first color-separated image signals, which represent a color, are converted to second color-separated image signals and a black signal, which together represent the same color, said color image processing apparatus comprising:
- logarithmic converting means for logarithmically converting input color signals into first color-separated image signals;
- minimum-value extracting means for extracting a minimum-value signal pixel by pixel based upon the first color-separated image signals converted by said logarithmic converting means;
- transformation means for subjecting both the first color-separated image signals and the minimum-value signal extracted by the minimum-value extracting means to a matrix transformation in accordance with prescribed transformation coefficients so as to produce second color-separated image signals and a black signal;
- and
- output means for outputting the second color-separated image signals and the black signal which are obtained by said transformation means,
- wherein the prescribed transformation coefficients are set so that a sum of prescribed terms related to the first color-separated image signals is one of 0 and a value approximating 0.
A color image processing method in which first color-separated image signals, which represent a color, are converted to second color-separated image signals and a black signal, which together represent the same color, said color image processing method comprising the steps of:
- logarithmically converting input color signals into first color-separated image signals;
- extracting a minimum-value signal pixel by pixel based upon the first color-separated image signals converted in said step of logarithmically converting;
- subjecting both the first color-separated image signals and the minimum-value signal extracted in said step of extracting to a matrix transformation in accordance with prescribed transformation coefficients so as to produce second color-separated image signals and a black signal;
- and
- outputting the second color-separated image signals and the black signal which are obtained by the matrix transformation,
- wherein the prescribed transformation coefficients are set so that a sum of prescribed terms related to the first color-separated image signals is one of 0 and a value approximating 0.
A color image processing method comprising the steps of:
- inputting first color-separated image signals and a minimum-value signal representing a minimum signal among the first color-separated image signals;
- performing a matrix calculation on both the first color-separated image signals and the minimum-value signal, the matrix calculation using correction coefficients, and obtaining second color-separated image signals and a black signal, the correction coefficients being set so that the second color separated image signals are substantially zero when the color represented by the first color-separated image signals is an achromatic color;
- and
- outputting the second color separated image signals and the black signal obtained by the matrix calculation.
Dependencies are inferred from the claim text.