RLE compression

摘要

RLE stands for run length encoding and takes advantage of repetitive values in data;in this case,runs of the same pixel colour.RLE has existed in displays and computing for at least 50 years.RLE is used in the JPEG image standard(although it is only part of the compression used there).It was also used by fax machines(remember them?.For our implementation,rather than storing bitmap data,the data encodes a run of pixels of the same state(on/off).The top bit indicates whether the pixels are on or off(ie,add 128 for on pixels),while the remaining seven lower bits encode the number of consecutive pixels with that property.Fig.b shows a glyph encoded using our RLE strategy.This small font is not a great example for this sort of compression,as the resulting data has ballooned from eight bytes up to 25 bytes.