Abstract: When the resolution for a specific gradation is enhanced, the resolution for the other gradations can be relatively degraded. It used to be difficult to carry out color conversion with accuracy in the high-lightness range without the occurrence of tone jump. A color conversion table which defines the correspondence between ink value data which specifies the ink quantities of inks in individual colors used in a printing device and the color component values of various colors used in another image device is generated. At this time, correction for interpolation accuracy enhancement is carried out beforehand so that colors in the low-lightness range will be larger in number than colors in the high-lightness range. This is intended to compensate the resolution which is relatively degraded in the low-lightness range by correction for resolution enhancement by interpolation accuracy. Thereafter, correction for resolution enhancement is carried out to create the ink value data.

Abstract: Colors look differently when observed under sunlight and room light. At least three chromatic colors and additional chromatic colors differing in hue from said three colors are used in combination. The additional colors are those which have a spectral reflectance which smoothens waviness in the spectral reflectance curve of the nearly achromatic color produced by the combination of the three chromatic colors. As the result, the combination of the colors gives rise to a color which has almost uniform spectral reflectance over the entire region of wavelengths. Thus it is possible to obtain printing which is less vulnerable to change in color under different light sources.

Abstract: A method which enables high-accuracy color conversion. On condition that conversion from a second color space into a first color space can be made accurately, target coordinates in the first color space are determined and coordinates in the second color space are arbitrarily determined. The coordinates in the second color space are converted into coordinates in the first color space and the difference between the resulting coordinates and the target coordinates is calculated. A trial for moving the coordinates in the second color space is repeated until the difference becomes smaller than a prescribed threshold. Therefore, the correlation between the first and second color spaces can be defined by repeating only the accurate conversion process so that color conversion can be accurately made over the whole color gamut according to the correlation thus defined.

Abstract: There is a need to print a large number of color chips for measurement of their hue, saturation, etc. Such colorimetry involves time-consuming work to create the tone correcting table.

Abstract: A color correcting unit receives color separation values such as CMY values from an image input unit. Under the control of a control portion, inputs to a first conversion portion constituted by a neural network which has been trained in advance on the basis of the spectral distribution of an arbitrary illuminant are corrected so that outputs from the first conversion portion satisfy the color separation values and a predetermined requirement. The input values to the first conversion portion, which satisfy the predetermined requirement, are sent to an image output unit. The image output unit outputs an image in accordance with these input values.

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.

Abstract: Colorimetric values such as L*a*b* values are transformed into color separation values such as CMYK values dependent on the characteristics of a color output device by using a multilayered feedforward neural network. The neural network learns in advance the relationships between a multiplicity of colorimetric values under different illuminants and color separation values. When colorimetric values of a standard illuminant and one of the color temperature of an observational illuminant, the spectral distribution of the observational illuminant, and colorimetric values at the time of illumination by the observational illuminant are inputted to the neural network, color separation values corresponding to one of the color temperature of the observational illuminant, the spectral distribution of the observational illuminant, and the colorimetric values obtained when illumination is provided by the observational illuminant are outputted.

Abstract: In a reproduced color correction system, a photometer measures external illuminant light and sends a measured result to a workstation. The workstation determines the type of an illuminant on the basis of the measured result and sends a selection signal and corresponding colorimetric value data to a neural network management unit. The neural network management unit is provided with a plurality of neural networks associated with types of illuminants. The neural network selected according to the selection signal converts the colorimetric value to a color separation value according to a post-learning transformation function. A color printing device outputs a color image on the basis of the generated color separation value. Thus, the neural network associated with the illuminant used for observation reference is selected, and appropriate color transformation is performed. Accordingly, even if the viewing condition is changed, color matching can be performed so that observed reproduced colors are unchanged.

Abstract: Color information such as a combination of fundamental colors in the subtractive or additive color mixing, hue, chroma and value in the psychological attributes of color, or coordinate values in a uniform color space are transformed nonlinearly and mutually by using a neural network, particularly a multi-layered feedforward neural network sufficiently trained of the transformation on samples of known data.