Run-length encoding

Atari ST - Savage Paint - PAC compression

Single bit plane. The five most common bytes in the image was followed by a run-length byte. It was simpler and gave a higher compression ratio than the run-length algorithm used in the .IFF format on the Amiga. The reason for using the 5 most common bytes was mainly because of the number of free registers in the MC68000 CPU.

Amiga - IFF - RLE compression

One or more bit planes. Runs longer than 2 bytes are encoded as -1 to -127 followed by the byte to be repeated (-n) + 1 times. Runs of different bytes are stored as 0 to 127 followed by n + 1 bytes of data. The byte code -128 is a no operation.

Head-On - BEAR3 compression

Indexed graphics, 8 bits per pixel. The range 0 to n was used by pixel data. The range n + 1 to 255 was the run lengths. Run-length = (byte - n) + 1. The main goals were fast, simple and compressible with ZIP for distribution.

RLC JPEG compression

For each value that is not 0, precede it with the count of 0's that went in front of the value. The result is a string of (count, value) pairs. If all the remaining vaules are 0 the block is terminated with an End Of Block marker (0, 0). The longest possible run is 15 to make sure the following Huffman coding is efficient. If a run is longer than 15 it is extended with pairs of (15, 0) which means 16 0's.

Unnamed

After a run of n symbols a run-length is inserted. That way no space is wasted on areas that do not compress and all symbols can still be used for data.

Stack-run based ideas

Each bit in a number is encoded with two bits, that way it is possible to signal the end of a number so each number can have a variable numebr of bits and there is no limit to the size of a number. If the number is increased by 1 before encoding, all numbers will have a 1 as the leftmost bit. That means it can be left out and the decompressor can just insert 1 to the left of the last decoded bit in the number.

Alternating runs and incompressible

00 - 0
11 - 1
10 - 0 end
01 - 1 end

Alternating black/white runs

00 - 0
11 - 1
10 - 0 end
01 - 1 end