Hewlett-packard Company

Michael M Chang

Ronald Albert Askeland

Amir Doron

Francis E Bockman

Jeff W Strain

A mask generation subroutine forms Z number of stacked n by m blank mask matrix arrays to provide a plurality of columnar mask locations. The subroutine then selects randomly any previously unselected column of mask locations from the stack of blank mask matrix arrays and assigns best print mode parameters to the individual mask locations in the selected column. The process of selecting and assigning is repeated until all columns of mask locations have been selected and all mask locations have been assigned best print mode parameters to provide a complete set of Z number of configured mask matrix arrays. A control program selects desired ones of the Z number of masks and applies the selected mask to control indicia patterns so that the depositing of indicia forming material in adjacent pixel locations is spaced in time to occur in different ones of the Z passes.

Method of generating randomized masks to improve image quality on a

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

Pixel-based image data are subsampled for transmission to a printer and later bilinear interpolation in the printer. The transmission system evaluates the error that will remain after interpolation. In response to this evaluation, the transmission system also forms trim data for later application to the interpolated subsample to remove a significant part of the error. Preferably trim data points are selected based on relative importance of the associated correction--specifically, size of the error that will remain after interpolation--but also the amount of trim data is controlled to maintain a significant advantage in overall transmission time, relative to transmitting the entire image-data set. The amount of trim data is held roughly to a certain fraction, about five percent, of the number of points in each data block (e. g., swath), essentially independent of the error evaluation. Preferably this controlled amount of trim data is padded out with zeroes to form a complete trim-data array--which is then run-length encoded. The encoded trim data and the subsample are sent to the printer. (Preferably pure-text portions are sent separately.) The printer applies the trim data to the interpolated subsample to obtain a better approximation to the original image data.

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San Diego, CA, United States of America

Michael M Chang