Tektronix, Inc.

Hewlett-packard Company

Patrick E Welborn

Christopher D Shaver

John Charles Dalrymple

David M Hall

Jeffery J Clark

Gregory P Thornton

Bo Lewendal

Brian G Crosby

Douglas I Haines

Described herein is a method of decompressing a compressed data stream from a data buffer. The compressed data stream is of a type having a plurality of compressed segments in a normal sequence, wherein each segment has a control element that specifies the length or number of following data elements. The method includes a step of reading the segments in their normal sequence from the data buffer. After reading a particular segment, its control element and data elements are reversed in order, and then rewritten to the data buffer in the original location of the segment. After reading and re-writing a plurality of the segments, the direction of reading can be reversed. That is, the segments can be read in reverse sequence. Because of the re-writing step, however, control elements will be read before data elements, thus enabling decompression even in the reverse direction.

Bi-directional data stream decompression

Data compression apparatus includes a current block of data bytes and a logic circuit for determining whether each byte in the current block is the same or different from a seed value. An encoding circuit produces a compressed version of the current block, which includes Command bytes and continuous literal data bytes from the current block. Each Command byte has an encoding identifier, an offset count and a data segment replacement count. Each offset count and data segment replacement count have, respectively, maximum bit sizes (and values). The encoding circuit responds to an indication that a data segment (1) differs from the seed value and (2) is followed by a series of contiguous data segments that are different from the seed value, by causing (a) a first Command byte to manifest a data segment replacement count of the maximum value and an offset count of 0 and to be followed by at least one of the contiguous data segments from the series. Thereafter, a next Command byte occurs if the remaining number of contiguous data segments exceeds the maximum value of the data segment replacement count. The next Command byte(s) each manifest maximum value data segment replacement counts until the count value .ltoreq. the data segment Replacement count. If the offset count is: greater than the offset count maximum value, the offset count is set to its maximum value. Subsequent Command bytes follow until the remaining offset count value is .ltoreq. to the maximum value or a lesser value.

Raster image data compression method and system

A system and method of printing an image on a substrate based on an input of detailed image intensity information for each of discrete pixel areas of the substrate, includes or performs steps of processing the detailed image intensity information into less detailed image intensity information; dithering the less detailed image intensity information to approximate the intensity resolution of the detailed image intensity information; and printing the dithered, less detailed, image intensity information onto the substrate. The system will use less memory space than a comparable system which prints directly from the detailed image intensity information, will minimize patterning effects, and will correct for artifacts which might otherwise be printed.

Improved color rendering method for intensity-variable printing based

A color processing system is provided that specifies color in a standardized, perceptually uniform color space and resolves color differences between input and/or output devices. The color processing system utilizes a color mapping techniques to adjust the results of color mapping to fit the color gamut of the output device. The color processing system may be implemented as a color rendering dictionary in a PostScript.RTM. Level 2 interpreter. An additional feature involves adaptation of PostScript.RTM. Level 1 applications to take advantage of the improved color processing system and PostScript.RTM. Level 2 flexibility.

Color processing system

A record in which a color is represented on a record medium at a selected gray scale level is created by resolving an addressable area of the record medium into a square array of addressable record locations and organizing the record locations into a plurality of groups each containing a 4.times.4 array of record locations. The groups are organized into a plurality of dither cells each containing a 4.times.4 array of groups, whereby each dither cell contains 256 addressable record locations. An [i+(j.times.16)]th gray scale level is established within a selected area of the record medium, where i is an integer in the range from zero to 16, j is an integer in the range from zero to 16 and [i+(j.times.16)] is an integer in the range from zero to 255, by addressing j record locations in each group of each dither cell within the selected area and addressing one additional record location in each of the i groups of each dither cell within the selected area, the j addressed locations in each group being substantially contiguous and being in substantially the same positions in their group as the j addressed locations in each other group, and the i groups which contain an additional addressed record locations being distributed substantially uniformly over the dither cell.

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Lake Oswego, OR, United States of America

Patrick E Welborn