Xerox Corporation

Thomas M Holladay

R Victor Klassen

Reiner Eschbach

Peter A Crean

Robert Roy Buckley

Norman W Zeck

L Bayles Holt

An improved technique for compressing a color or gray scale pixel map representing a document using an MRC format including a method of segmenting an original pixel map into two planes, and then compressing the data or each plane in an efficient manner. The image is segmented such that pixels that compress well under a lossy compression technique are placed on one plane and pixels that must be compressed losslessly are placed on another plane. Lossy compression is then applied to the lossy pixel plane while lossless compression is applied to the lossless pixel plane.

Method and apparatus for segmenting a composite image into mixed raster content planes

A system for producing a desired final halftone color. The system includes a plurality of halftone dot sets. Each dot set includes a plurality of halftone cells. Each halftone cell has a distinct number of sub-cells. Actual halftone levels of a plurality of component colors are produced by each halftone cell as a function of a number of the sub-cells within the halftone cell being selected. Combinations of the actual halftone levels of the respective component colors within each dot set producing respective actual final colors are associated with each of the dot sets. A database stores, for each dot set, the actual halftone levels for each component color produced by each halftone cell. A closest actual halftone color to the desired final halftone color is determined as a function of a combination of the actual halftone levels stored within the database for the respective component colors within one of the dot sets. The closest actual halftone color is produced using a color printer.

Method of producing spot colors appearance with process color printing

A method of reducing visible image artifacts that utilizes variable phase parameters (i.e., the standard x, y start position in halftone cells) during halftoning processes to match the phases of halftone cells, and further utilizes a brick approach to halftoning. The position in a halftone dot structure is correlated to the phase of sine waves for subsequent dots to be used in a halftoning process. Utilizing a selected x, y start position in halftone cells to match phase parameters of said halftone cells according to said position of said halftone dot and said subsequent dots. Switching from one dot to another dot on the same new starting position in the second dot will improve the probability that the thresholds and the slopes of the halftone dots are matched at the boundary between the two different dots.

Using the phase information in the halftone dot structure to minimize

An image processing system for preparing a color document for printing, each discrete area or pixel in the image described by a signal having a number of possible states greater than can be rendered by a selected printer, in which each separation of the image is halftoned, with at least one of the separations processed with a non-periodic halftoning method, and at least one of the remaining separations processed with a periodic pattern. Preferably, in a printer printing with colorants approximating cyan, magenta, yellow and black, one of the non-yellow separations is processed with the non-periodic halftoning method.

Hybrid quantization method for color document reproduction

A method for digitally printing a digital image by reference to a succession of code words representing blocks of pixels of the original image. The image is originally subdivided into uniform size blocks of pixels. Each of the blocks of pixels is given a unique identifier unless it is identical to any of the previously scanned blocks. Identical groups are given the same identifier. In printing the digital image, the identifiers are scanned in sequence and the corresponding pixel blocks are successively stored in buffer memories for modulating the printer.

Tile encoding in image printing

An electrical screening system for binary displays or binary graphic recording systems is disclosed which suppresses false contours. The suppression is achieved by increasing the number of gray levels that a given m.times.n matrix of pixels can represent. Each pixel can only represent one of two gray levels in a binary display or graphic system. A conventional m.times.n halftone cell is able to reproduce m.times.n+1 gray levels. The extra gray levels above the m.times.n+1 quantity are achieved for a given m.times.n halftone cell by dynamically changing the values of the m.times.n screen signals associated with a halftone cell. The amount of the change is limited to a value between zero and D inclusive where D is the difference between two adjacent screen signal values.

Method and apparatus for reduction of false contours in electrically

An electronic signal representing the density of pixels in a scanned line in an original image and containing pixels in whole number multiples of a single line of halftone screen partial dot values plus a predetermined extension parameter is electronically halftoned by comparing the pictorial signal with the single line of halftone screen partial dot values to form an electronic halftone image. An electronic screen function represented by the single line of halftone screen values, produces automatically a rotated halftone screen at a predetermined angle to the original electronic image when the number of pixels in the input, scanned line of the original document is set equal to a whole number multiple of the number of partial-dot values plus a predetermined extension parameter. Under these conditions, the scanned input is automatically halftone screened electronically into halftone cells approximating a parallelogram and having said predetermined angle. The single line of partial-dot values need only be circularly buffered through a comparator. No electronic indexing or shifting of partial-dot values is required.

Electronic halftone screening

An electronic signal representing the density of a scanned image is electronically halftoned by combining the pictorial signal with a rectangular array of halftone screen values to form an electronic halftone image. The electronic screen function represented by the array of halftone screen values is rotated at variable angles to the original electronic image by defining a repetitive rectangular matrix representative of any predetermined halftone cell approximating a parallelogram and incorporating a shifting parameter for the repetitive rectangular matrix. An efficient, high speed, partial-dot halftoning technique is performed by indexing the screen function rectangular array, under the supervision of the shifting parameter, against the scanned image values for a realtime serial combination of the functional values.

Growing community of inventors

Webster, NY, United States of America

Thomas M Holladay