Hewlett-packard Company

Hewlett-packard Corporation

Paul H Dillinger

Alexander Perumal, Jr

Timothy M McDonough

Francis E Bockman

Jeffrey S Best

A computerized method, containable in a computer memory device, is disclosed for tristimulus color space coordinate data nonlinear storage, retrieval, and interpolation, and, more specifically to memory mapping and data interpolation for 24-bit L*H*C* to 24-bit RGB color mapping (three 8-bit words to each coordinate). Predetermined output tristimulus color space coordinate data points are stored in nodes of a memory construct based upon use of input values of a cylindrical-based tristimulus color space coordinate system, where a non-linear selection of stored data points is provided in the memory construct. The number of linear interpolations of each of the coordinates is determined by the number of available bits in each data word after providing sufficient bits to address the surrounding stored nodes. Each coordinate conversion is expedited by caching frequently accessed nodes in an auxiliary cache memory, by node doubling of preselected nodes, and by fetching only relevant adjacent nodes during interpolation.

Method for interpolation of tristimulus color data

Device-space color specifications for two color-presentation devices are interrelated through the intermediary of at least one perceptual color space. This interrelation is performed by either tabulations or real-time software processing, and in such a way that color, and color changes, specified in relation to one device--in a control language of that device--are tracked in both the language and the actual performance of the other device. This mapping through perceptual space can be used to produce the effect of matching the two device gamuts to each other, so that the full gamuts of both are in effect merged. When so used, this new kind of mapping preserves relative positions in color space--and thus the capability of the tracking device to maintain distinctions between colors seen on the source/input device that appear very closely similar. Such discrimination between adjacent colors can be supported essentially throughout the gamut of both devices and in particular even very near the lightness extrema and maximum-saturation point on a hue page. A related technique of merging two- or three-dimensional color elements can be used either to implement the new mapping, or for very different purposes such as converting colors from perceptual into machine space.

Coordinating color produced by two devices--using a hue-controlled

This system selectively enables a printer to deposit primary or black color dots at pixel locations on a sheet to produce a color image--in such a way as to increase the overall number of dots used in the image, thereby minimizing contrast between dots on the sheet and adjacent areas and so providing a better simulation of a continuous-tone image. The result is print quality often near that of error diffusion, usually better than any dither technique, but with the greater speed of a dither technique. The system includes a memory for storing a first color vector for each pixel in the image, respectively, and a processor coupled to the memory for determining a second color vector from each of the first vectors, respectively. The processor accomplishes this determination by replacing a fraction of the black color component of the first vector with primary colors. Preferably the processor also removes from the first color vector a quantity of white, in conjunction with the black replacement; in this case the processor sets the fraction of the black component to a value between zero and one inclusive, depending on the quantity of white that is available, in the first color vector, for removal. Preferably the fraction is the smaller of (1) the quantity of black present and (2) a certain fraction of the quantity of white available for removal. Analogously a fraction of the secondary color component of a color vector is replaced with primary colors.

Color digital halftoning using black and secondary color replacement

Device-space color specifications for two color-presentation devices are interrelated through the intermediary of at least one perceptual color space. This interrelation is performed by either tabulations or real-time software processing, and in such a way that color, and color changes, specified in relation to one device--in a control language of that device--are tracked in both the language and the actual performance of the other device. This mapping through perceptual space can be used to produce the effect of matching the two device gamuts to each other, so that the full gamuts of both are in effect merged. When so used, this new kind of mapping preserves relative positions in color space--and thus the capability of the tracking device to maintain distinctions between colors seen on the source/input device that appear very closely similar. Such discrimination between adjacent colors can be supported essentially throughout the gamut of both devices and in particular even very near the lightness extrema and maximum-saturation point on a hue page. A related technique of merging two- or three-dimensional color elements can be used either to implement the new mapping, or for very different purposes such as converting colors from perceptual into machine space. A new radial-displacement surface scaling also preserves relative color information by avoiding lightning-rod effects at the lightness extrema, and at the maximum-saturation point.

Method for tristimulus color data non-linear storage, retrieval, and

The invention is for use with a visible medium capable of light reflection etc., and for use with a color-image source that defines a desired color. Here a device for causing the medium to appear colored includes a gray-scale subsystem to achromatically suppress a stated fraction of the reflection; and at least two device-primary subsystems to cause selective reflection of light of two associated device-primary colors. Even if the device, as originally made, in effect uses the gray-scale subsystem to help construct colors, or the device-primary subsystems to help form gray-scale 'values', such cross-dependency is essentially removed. A programmed processor resolves the desired-rendition information into Fraction-Black, Fraction-Colorant, and hue. Fraction-Black information is applied exclusively to control only the gray-scale subsystem; Fraction-Colorant to control only the device-primary subsystem; and hue to select a dominant and a subordinate primary subsystem and as between them apportion the Fraction-Colorant.

Apparatus for forming color images, using a hue-plus-gray color model

A technique of merging or 'matching' hue pages of a CRT and printer is used to map CRT control signals through a common perceptual space into printer control signals. The system (1) receives a color specification expressed as CRT control signals, (2) locates the specified color within the CRT perceptual gamut, (3) normalizes the two gamuts in perceptual space, (4) determines the relative position of the same color in the normalized CRT gamut, (5) declares that position to be the relative position of that color in the normalized printer gamut as well, (6) unfolds the normalization to determine the absolute position of the color in the actual printer gamut, (7) expresses that position in terms of printer-control signals, and then (8) applies those signals to the printer, to print the specified color. As a result that color, and color changes, specified in terms of CRT control signals are tracked in terms of both printer control signals and actual printer performance. The two device gamuts are in effect mapped to each other; the full gamuts of both are in effect merged. This new mapping preserves relative positions in color space--and thus the capability of the printer to reproduce distinctions between colors seen on the CRT that appear very closely similar. Such discrimination between colors very adjacent in color space is supported nearly throughout gamuts of both devices, even very near the lightness extrema and maximum-saturation point on a hue page. To facilitate processing, the normalized characterizations for the CRT and printer gamuts (taken as triangular) are approximated for each of 360 hue pages by single-point data representing lightness and chroma at the saturation point--or normalized lightness at that point--plus two common lightness extrema for the gamut solid.

Printing with full printer color gamut, through use of gamut

Provided is a system and method for selectively enabling a printer to deposit on a sheet cyan, magenta, yellow and black (C,M,Y and K) primary or black color dots at each of the plurality of pixel locations to produce a color image. The system comprises a memory for storing C, M, Y and K values for each pixel in the color image and a processor for controlling selective deposition of the C, M, Y and K colors. The system includes a memory for holding a color vector for each pixel, respectively in the color image; a memory for storing parameters of a dither cell; and a processor coupled to the memory for comparing the dither cell with each color vector, to select a color component to print at the corresponding pixel location based on the comparison. The system provides a halftoning technique that produces print quality near error diffusion quality with the speed of a dither by dithering on a color vector. The replacement of black and secondary colors by the system produces better print quality than other dither techniques.

Color digital halftoning using black and secondary color replacement and

Apparatus for forming color images using a hue-plus-gray color model

The invention is for use with a visible medium capable of light reflection etc., and for use with a color-image source that defines a desired color. Here a device for causing the medium to appear colored includes a gray-scale subsystem to achromatically suppress a stated fraction of the reflection; and at least two device-primary subsystems to cause selective reflection of light of two associated device-primary colors. Even if the device, as originally made, in effect uses the gray-scale subsystem to help construct colors, or the device-primary subsystems to help form gray-scale 'values', such cross-dependency is essentially removed. A programmed processor resolves the desired-rendition information into Fraction-Black, Fraction-Colorant, and hue. Fraction-Black information is applied exclusively to control only the gray-scale subsystem; Fraction-Colorant to control only the device-primary subsystem; and hue to select a dominant and a subordinate primary subsystem and as between them apportion the Fraction-Colorant. These parameters are used not only in color selection but also in halftoning, where they enable colorant choice at each pixel in terms of input color rather than after resolution into pigment terms; this capability is used to prevent color artifacts such as pixels of pigment irrelevant to the desired color.

Growing community of inventors

Escondido, CA, United States of America

Paul H Dillinger