Method for compression and transmission of video information

Abstract

A facsimile transmitter capable of transmitting graphic as well as text material, by telephone or wireless. A digital code derived from scanning the document to be transmitted is truncated from eight bits per pixel to six bits per pixel. The three most significant bits of each pixel are run length encoded in eight bit bytes, so that wherever the same three most significant bits appear in adjacent pixels, these three bits are transmitted once, followed by a five bit code indicating the number of times (up to 32 times) the same three most significant bits are repeated in succeeding pixels. The resulting eight bit bytes are similarly run length encoded, so that the transmission of the three most significant bits of each pixel is double run length encoded. An eight bit fine resolution byte is transmitted for each eight pixels. The fine resolution bytes are encoded so that, in conjunction with the double run length encoded three most significant bits of each pixel, (i) the entire six bits of one-fourth of the pixels, (ii) the most significant four bits of one-fourth of the pixels, intermediate between the six-bit pixels, and (iii) only the three most significant bits of one-half of the pixels, each disposed between a six bit pixel and a four bit pixel, are transmitted. At the receiving end the pixels having four bits are expanded to eight bits by averaging the values of the preceding and succeeding pixels for which six bits were transmitted. Then the pixels having three bits are expanded to eight bits by averaging the values of the immediately preceding and immediately following pixels. Each transmitted scanned line contains an error detecting code. When an error is detected in a scanned line at the receiving end, the pixels of that line are replaced by the average of the corresponding pixels of the immediately preceding and succeeding lines.