Mespotine-RLE-basic v0.9 - An overhead-reduced and improved Run-Length-Encoding Method

Run Length Encoding(RLE) is one of the oldest algorithms for data-compression available, a method used for compression of large data into smaller and therefore more compact data. It compresses by looking at the data for repetitions of the same character in a row and storing the amount(called run) and the respective character(called run_value) as target-data. Unfortunately it only compresses within strict and special cases. Outside of these cases, it increases the data-size, even doubles the size in worst cases compared to the original, unprocessed data. In this paper, we will discuss modifications to RLE, with which we will only store the run for characters, that are actually compressible, getting rid of a lot of useless data like the runs of the characters, that are uncompressible in the first place. This will be achieved by storing the character first and the run second. Additionally we create a bit-list of 256 positions(one for every possible ASCII-character), in which we will store, if a specific (ASCII-)character is compressible(1) or not(0). Using this list, we can now say, if a character is compressible (store [the character]+[it's run]) or if it is not compressible (store [the character] only and the next character is NOT a run, but the following character instead). Using this list, we can also successfully decode the data(if the character is compressible, the next character is a run, if not compressible, the next character is a normal character). With that, we store runs only for characters, that are compressible in the first place. In fact, in the worst case scenario, the encoded data will create always just an overhead of the size of the bit-list itself. With an alphabet of 256 different characters(i.e. ASCII) it would be only a maximum of 32 bytes, no matter how big the original data was. Many image/audio/video-formats who apply Standard-RLE(FLAC, TIFF, etc), could benefit from Mespotine-RLE heavily by getting rid of the negative side-effects of Standard-RLE. Even datacompression programs that use RLE as main compression-method or as a pre-processor, could be improved by Mespotine-RLE. Mespotine, Méô: “Mespotine-RLE-basic 0.9, an overhead-reduced & improved Run-Length-Encoding Method”, 2015 trss.mespotine.de, [email protected]