Method and apparatus for correction of color shifts due to illuminant changes
First Claim
1. A color reproduction method for effecting color matching for a plurality of different color reproduction devices for reproducing the color of an original color image, comprising the steps of:
- setting an intermediate color representation system which is represented by at least three characteristic parameter values obtained by multivariate analysis of a spectral reflectance or a spectral transmittance which is not dependent on an illuminant;
learning a first neural network such that, when at least three color information values peculiar to each of said color reproduction devices are inputted, said at least three characteristic parameter values of said intermediate color representation system corresponding to said inputted color information values are outputted, and learning a second neural network such that, when said at least three characteristic parameter values of said intermediate color representation system are inputted, color information values corresponding to said inputted characteristic parameter values are outputted;
transforming said at least three color information values peculiar to a first color reproduction device into said at least three characteristic parameter values of said intermediate color representation system by using said first neural network which has been learned;
transforming said at least three characteristic parameter values under a constraint concerning colorimetric values of colors reproduced by said first color reproduction device and a second color reproduction device different therefrom; and
transforming said at least three characteristic parameter values transformed under the constraint, into color information values of said second color reproduction device by using said second neural network which has been learned, so as to effect color matching for said plurality of different color reproduction devices.
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Abstract
Color separation values such as CMYK values from an input device are transformed into characteristic parameter values by a first transforming device having a neural network which has undergone learning in advance in such a manner as to output characteristic parameter values obtained by multivariate analysis of spectral distributions which correspond to the color separation values and are illuminant-independent. These characteristic parameter values are subjected to a linear transformation by a second transforming device, the linear transformation having a constraint that calorimetric values under a specified illuminant are to be equal or another similar constraint, by using mean vectors and eigenvectors (principal component vectors) of predetermined spectral reflectances stored in a storage device. The transformed characteristic parameter values are transformed into color separation values of a target color reproduction device by a third transforming device having a neural network which has undergone learning in advance.
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Citations
15 Claims
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1. A color reproduction method for effecting color matching for a plurality of different color reproduction devices for reproducing the color of an original color image, comprising the steps of:
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setting an intermediate color representation system which is represented by at least three characteristic parameter values obtained by multivariate analysis of a spectral reflectance or a spectral transmittance which is not dependent on an illuminant; learning a first neural network such that, when at least three color information values peculiar to each of said color reproduction devices are inputted, said at least three characteristic parameter values of said intermediate color representation system corresponding to said inputted color information values are outputted, and learning a second neural network such that, when said at least three characteristic parameter values of said intermediate color representation system are inputted, color information values corresponding to said inputted characteristic parameter values are outputted; transforming said at least three color information values peculiar to a first color reproduction device into said at least three characteristic parameter values of said intermediate color representation system by using said first neural network which has been learned; transforming said at least three characteristic parameter values under a constraint concerning colorimetric values of colors reproduced by said first color reproduction device and a second color reproduction device different therefrom; and transforming said at least three characteristic parameter values transformed under the constraint, into color information values of said second color reproduction device by using said second neural network which has been learned, so as to effect color matching for said plurality of different color reproduction devices. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A color imaging apparatus for effecting color matching for a plurality of different color reproduction devices for reproducing the color of an original color image, said color imaging apparatus comprising:
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input means for converting at least three color information values into electrical signals; storage means for storing eigenvectors and mean vectors of spectral reflectances of reproduced colors by a first color reproduction device and a second color reproduction device which are obtained by performing the multivariate analysis of spectral reflectances in advance, connection weights of two neural networks which have been learned in advance, a spectral distribution of at least one illuminant, and color matching functions; first transforming means adapted to transform the electrical signals from said input means into electrical signals corresponding to characteristic parameter values; second transforming means for transforming the electrical signals from said first transforming means by a linear transformation having a condition that colorimetric values of a subject color and those of a reproduced color under a designated illuminant are equal, or that a mean color difference value between a subject color and a reproduced color measured under a plurality of designated illuminants is minimized; third transforming means adapted to transform characteristic parameter values of said second color reproduction device outputted from said second transforming means into electrical signals corresponding to color information values of said second color reproduction device; and output means for outputting as output signals the electrical signals outputted from said third transforming means. - View Dependent Claims (12, 13, 14, 15)
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Specification