Facsimile and static presentation processing – Facsimile – Specific signal processing circuitry
Patent
1992-05-15
1994-10-25
Coles, Sr., Edward L.
Facsimile and static presentation processing
Facsimile
Specific signal processing circuitry
358456, 358429, 358433, 358457, 358465, 358466, H04N 141, H04N 1415, H04N 140
Patent
active
053594304
ABSTRACT:
A digital image processing system for convening continuous-tone images into halftone images to be output by a receiver with limited storage capacity. The continuous-tone image is converted into a first halftone image by threshold screening. Threshold screening involves comparing the pixel values of blocks of the continuous-tone image with cell values of a threshold array and turning on pixels of a first halftone image according to whether the pixel values of the continuous-tone block are greater than or equal to the cell values of the threshold array. The threshold array is associated with a plurality of gray patterns. A block count is determined which equals the number of pixels of each block of the first halftone image that are tuned on. A second halftone image is produced by combining gray patterns corresponding to the block counts. An error image is produced by determining differences between the first halftone image and the second halftone image. Scattered pixels in the error image are removed. The error image is compressed and sent to the receiver along with the block counts. The receiver produces a final output halftone image by reversing the process that was used to create the error image.
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Ulichney, R., "Digital Halftoning," The MIT Press, Cambridge, Mass., 77-99, 1987.
Coles Sr. Edward L.
Microsoft Corporation
Williams Kimberly A.
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