Hewlett-packard Company

Francis E Bockman

Guo Li

Kirt Alan Winter

Joseph M Torgerson

Paul H Dillinger

Michael M Chang

David Charles Towery

The present invention is embodied in a system and method for automatically calibrating the print contrast of an inkjet printing system using an optical-electronic sensor to detect an ink drop volume. The print contrast calibration system includes an optical-electronic sensor that obtains test pattern data from a printed test pattern, a calibration module that contains calibration data for the printing system, an installation module that determines a drop volume score by using the test pattern data and the calibration data and a printing module that determines a print contrast setting based on the drop volume score. The present invention also includes a method for calibrating print contrast in a printing system by storing standard calibration curves for the printing system, comparing the standard calibration curves with a printhead assembly calibration curve to determine a drop volume score, and setting the print contrast based on the drop volume score.

Calibration of print contrast using an optical-electronic sensor

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. Preferably the system minimizes granularity in highlight or near-yellow regions of a printed image by causing cyan colorant and magenta colorant in highlight or near-yellow regions to be deposited exclusively remote from one another. Preferably the steering system include portions of a lookup table, and the minimization is effected by contours (preferably diagonal) of permitted cyan and magenta colorant deposition within the table. The invention also includes a method of preparing the table.

Reducing granularity in highlights and yellow fields by plane-dependent tables, in device-state error diffusion

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.

Multi-pass inkjet printer system and method of using same

An automatic system forms color LUTs (or LUT-forming data) for automated reference&mdash;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. In a related fifth aspect, one state is assigned to each major entry based on, at a gamut surface except at the dark end, favoring states nearer the surface over those nearer a desired major entry; and at the neutral axis, especially its dark end, favoring real black. Other assigning is best done by entry nearness. In a sixth aspect preferably 1D LUTs are formed for finding major entries based on an input-color spec, not monotonic in entry assignment to indices; precomputed ED distributions attach to indices. In a seventh aspect a state LUT formed to access states based on input specs is used to print nominal neutral colors and measured results used to adjust access. In an eighth facet related to the first, the ramps correspond to fundamental combinations of single colorants, e. g. secondaries.

Constructing device-state tables for inkjet printing

One form of the printer inks multiple tonal levels, as for continuous-tone images. A generally randomized printmask controls the printer. What is randomized is, for each pixel respectively, an indicator of whether to print or not. Each indicator is, preferably, a discriminator number for comparison with desired-image data--specifically with a desired tonal level, at each pixel, for the desired color image--to make each printing decision. Preferably the printer is thereby deciding whether to deposit a certain number of drops per pixel; it compares the discriminator with a particular number of desired drops, for the desired image. The discriminator at each pixel is in general different for multiple passes and these discriminators for the passes form a sequence. The sequence, for each pixel., is preferably selected at random from a multiplicity of sequences. Preferably the sequence for each pixel is preselected at random; and the selected sequences for all pixels are prestored in nonvolatile memory. To do this, preferably each sequence is numbered and the sequence for each pixel is selected by randomly selecting a sequence number. Another preferred form of the printer is not necessarily multilevel but the sequences are selected as just described. A method is included for initial construction, and storage on a tangible medium, of the sequences--and later recall and use.

Random printmasks in a multilevel inkjet printer

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.

Device state error diffusion technique for halftoning

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). In response to that selection, control signals are altered to the printheads in accord with component color values that are initially established for the matrix position that is now occupied by the image selected as the reference image. Such component color values are thereafter used to correct for subsequent printing.

Method and apparatus for ink jet printer color balance calibration and

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

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. The processor is responsive to a determined match to access the second entry at the address and to employ the second entry to control the color printer. Exclusion of the LSB's in determination of the presence of a match enables a substantially greater probability of finding such a match in the cache memory.

Cache memory system for a color ink jet printer

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. If they are, the transfer functions are averaged and employed to calibrate colors transmitted to an attached color printer. If they are not within the transfer function threshold value, an additional comparison test is made. If the resulting transfer function is not within the threshold value, a default color transfer function is substituted.

Growing community of inventors

San Diego, CA, United States of America

Francis E Bockman