None-of-the-above digital halftone compression and decompression
View Patent ↗An improved method of encoding and compressing digital halftones that utilizes a “none-of-the-above” method for designating variable-length runs. A monochrome input bitmap is rearranged slightly to reduce the patterns possible in contained digital halftone cells. This revised monochrome bitmap is parsed into subfiles to optimize run-lengths. The parsed subfiles are combined into a single file whose alternating runs of 1's and 0's are converted into successive variable-length binary numbers. One of the permutations of an antecedent binary is designated “none-of-the-above” and its use triggers a subsequent variable-length binary. All other permutations within each variable-length binary may designate a specific contained run-length and such use triggers a return to the initial binary in the series. The above method is reversed to decode and uncompress the encoded file to reproduce the original revised monochrome bitmap for display by a computer monitor or printer.
1. A method for compressing and decompressing a digital halftone monochrome bitmap comprising the steps of:
(a) obtaining an input digital halftone monochrome bitmap of dimensions in pixels high and wide such that a plurality of equal-sized multi-pixel halftone cells are wholly contained,
(b) reducing the possible patterns of monochrome pixels within said halftone cells by shifting certain pixels either horizontally or vertically according to a master grid based on a checkerboard pattern,
(c) parsing said revised halftone cells into individual files, one each for each pixel position within the cell,
(d) recombining said files into a single file,
(e) encoding said single file's alternating runs of two monochrome colors with variable-length binary numbers within which all but one binary permutation may designate the length of the run and a return to start, and one binary permutation designates none of the contained run-lengths and to move on to larger successive binary numbers,
(f) generating the increasing sizes of said successive run-length-containing variable-length binary numbers by a plurality of means, including Fibonacci numbers, byte-length-based numbers, or other means based on efficiency,
(g) generating a compressed file of fewer bits than the input bitmap by utilizing steps (a)-(f),
(h) reversing said method in steps (b)-(g) until said compressed file is uncompressed to replicate the said reduced pattern bitmap,
(i) displaying said bitmap on a computer printer or monitor.