Abstract: A state transition display window displays a hue circle and a number of setting points corresponding to respective color adjustment levels. As the user makes color adjustments, a history of the color adjustments is displayed in the form of arrows connecting related setting points. If the user specifies two setting points, images corresponding to setting point located on the line connecting the two specified setting points are displayed on an image display subwindow. A current image and six images adjacent thereto are displayed in a 6 near images display window.

Abstract: Three-dimensional LUTs produce a lightness signal L* from input color signals C, M and Y. The three-dimensional LUTs are respectively provided for four divisional sections of an input color signal K. A three-dimensional LUT switching device judges to what section a current value of the input color signal K belongs. A selector selects one of the LUTs in accordance with a judgment result. Similar processing is performed for chromaticity signals a* and b*. According to another aspect of the invention, three-dimensional LUT color converters produce color signals L.sub.2 *, a.sub.2 * and b.sub.2 * based on only input color signals C, M and Y. A position in the L*a*b* space of the color signals L.sub.2 *, a.sub.2 * and b.sub.2 * has a deviation from a position of color signals L.sub.1 *, a.sub.1 * and b.sub.1 * to be output actually. Based on an input color signal K, a one-dimensional LUT produces a lightness signal L.sub.3 *, which corresponds to the deviation.

Abstract: A color image processing system for generating recorder image signals of four colors containing India ink from three color signals, the color image processing system includes a converter for converting three color signals into separated brightness and chromaticity signals; a range converter for converting the brightness signal into a range converted brightness signal which is within a record color reproduction range; an edge detector for obtaining an edge amount signal from the range converted brightness signal; a chroma detector for detecting chroma of an image signal from the chromaticity signal; an edge enhancer for enhancing an edge part of an image represented by the range converted brightness signal; a smoothing circuit for smoothing the range converted brightness signal; a brightness and chromaticity converter which includes a converter for executing brightness conversion by mixing an output of the edge enhancer and an output of the smoothing circuit according to the edge amount signal detected by the

Abstract: Binary data corresponding to respective lattice point data addresses of a direct look-up table and indicating an inside or outside of a color reproduction range of an output device are retained. Based on the binary data, a judgment is made of whether an input color signal is located inside or outside the color reproduction range of the output device. A lattice point data address that is generated from the input color signal is compressed based on a result of the above judgment. The judging and compressing operations are repeated to generate lattice point data addresses so that they are located inside the color reproduction range of the output device.

Abstract: The CiMiYi signals of input CiMiYiKi signals are converted into CoMoYo signals of CoMoYoKo signals by using three-dimensional LUT color converting devices. The Ki signal of the input CiMiYiKi signals is subjected to gradation conversion to obtain the Ko signal of the CoMoYoKo signals by using a one-dimensional LUT.

Abstract: A first nonlinear conversion section converts input color signals of a kind that is one of plural, different kinds to L*a*b* signals. A second nonlinear conversion section converts the L*a*b* signals to image recording signals of four colors including black. The first nonlinear conversion section includes an input judgment device for judging the kind of input color signals, a weight memory for storing weights for the respective kinds of color signals, and a nonlinear conversion circuit. The weights corresponding to the kind of input color signals identified by the input judgment device are read from the weight memory and set in the nonlinear conversion circuit. The first nonlinear conversion section further has a learning device to accommodate color signals whose conversion relationship with the L*a*b* signals has not been defined.

Abstract: A lightness/chromaticity separation device converts three input color signals to {L*, a*, b*} signals. A chroma determination device determines a chroma signal C* based on the {a*, b*} signals. An UCR ratio calculation device calculates an UCR ratio .alpha. according to a C*-.alpha. function that is adjustable by changing parameters. A nonlinear conversion circuit determines output color signals of four colors including black based on the {L*, a*, b*} signals and the UCR ratio. The nonlinear conversion circuit includes a network-type combination of a plurality of analog nonlinear operation units.

Abstract: Three input color separation signals are converted to three color signals on a uniform color space. A black quantity to be used for full-black reproduction is determined as the maximum black quantity of an output black signal. Then, an actual black quantity of the output black signal is determined based on the maximum black quantity and a chroma signal obtained from the uniform color signals. Finally, color quantities of respective output color signals other than the output black signal are determined based on the uniform color signals and the actual black quantity thus determined.