Abstract: Incremental printing apparatus preferably includes a system for steering the error-diffusion system to respond, to a near-gray or near-yellow input color, with a preselection of a color toward one color plane or toward another color plane. This is not a threshold system. Preferably the steering system operates toward one of the color planes depending on which plane is closer to an input color signal (which includes accumulated error from pixels processed previously, as well as the original signal for a pixel being processed). Preferably the apparatus essentially forecloses use of different inks in adjacent pixels, as distinguished from only modifying a likelihood of using different inks. Preferably the system operates in particular portions of color space that are near a yellow axis. Preferably the two color planes are a cyan and a magenta plane.

Abstract: An inkjet color printer accesses image data to be printed on a pixel by pixel basis and determines the Z number of drops of different color inks to distribute per pixel over a predetermined number of passes in a multi-pass print mode of operation. Predetermined constraints relative to the maximum number of drops of a single ink color per pixel and per pass permit maskless drop ordering and an even distribution of ink over time per pixel.

Abstract: An automatic system forms color LUTs (or LUT-forming data) for automated reference—typically in error diffusion (ED). A first aspect is for printers with six or more colorants. Three ramps, for different basic colorants, are photometrically measured; mainly just those results yield a transform from 3D color to system colorants. In a second aspect, some device-state candidate colors are chosen for black replacement. In a variant the choice is subject to (1) maintaining some chromatic colorant in each pixel with black; or (2) modifying use patterns to avoid alternative use of composite black vs. black; or (3) adjustments to allow for composite nonequivalence to black. A related third aspect allows replacement only if there is a given minimum amount of composite. In a fourth aspect, candidate states are dropped that have small changes in number of quanta per pixel, or no companion light colorant quantum with each dark one, best eliminating those with too many quanta of each or all colorants.

Abstract: A halftoning technique is disclosed which uses look-up tables to identify a combination of color ink drops (device states) to be printed by an inkjet printer. The look-up tables are indexed by a particular color to be reproduced. An error is also output by the look-up tables reflecting the difference between the indexing tone level and the printed color spot. The error is applied in a halftoning process to neighboring pixels. A plurality of look-up tables is used, and one of the look-up tables is selected for a particular medium (e.g., glossy paper, plain paper) to be printed upon. In this manner, the number and combination of ink drops can be optimize for a particular type of medium. In one embodiment, six different color inks are used by the printer.

Abstract: A method, for adjusting the color balance of printheads in a color printer, utilizes a matrix of image data including a reference image data set for a reference image and a plurality of color modified image data sets for plural color modified images. The reference image data set includes in-balance component color data values and each of the color-modified image data sets include out-of-balance component color values. A printer is controlled to operate the printheads to print the reference image and each of the color modified images at pre-determined locations on a media sheet in accord with the matrix of image data. If the printheads are not properly adjusted, the printed reference image and each of the color modified images appear positionally offset on the media sheet. A user, upon examining the media sheet selects one image on the media sheet as the reference image (e.g., the image which exhibits best black/white characteristics and contrast).

Abstract: 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.

Abstract: A color printer receives P, N-bit values indicating a computer generated color to be printed, there being 2.sup.NP possible combinations of bits in the P, N-bit color values. Each N-bit value has a least significant bit (LSB). Upon receiving P, N-bit color values, the color printer creates an address from P combined multiple-bit segments of each of the received N-bit values, each multiple bit segment excluding at least a LSB of each N-bit value. The color printer includes a cache memory having substantially less addresses than 2.sup.NP, each cache address including first and second entries, a first entry being P values indicative of a computer generated color and a second entry being P values usable by the color printer to reproduce the first entry. A processor determines if there is a match at an address created from a received computer color value between a first entry and the received computer color value, the match disregarding an LSB of each N-bit value comprising the first entry at the address.

Abstract: A color display screen displays a calibration color patch and a comparison color patch. The calibration color patch manifests a calibration color of a predetermined intensity, and the comparison color patch manifests a comparison color derived from a user determined input value. The system is controlled by a processor and is responsive to a user's indication of a perceived color match between a calibration color patch and a comparison color patch, to determine a transfer function that enables conversion of a value that generated the comparison color to a value assigned to the calibration color. The processor is further responsive to further perceived color matches of first and second color patches with first and second different intensity calibration color patches, respectively, to determine if first and second transfer functions determined for the first and second comparisons are within a transfer function threshold value of each other.