Color Cell Compression

Color Cell Compression is an early lossy image compression algorithm first described by Campbell et. al. in 1986.^[1] It is a variant of Block Truncation Coding.^[2] The encoding process works on small blocks of pixels. For each block, it first partitions the pixels in that block into to two sets based on their luminance values, then generates representative colour values for each of these sets, and a bitmap that specifies which pixels belong to which set. The two colour values and the bitmap for each block are then output directly without any further quantization or entropy coding.

The decoding process is simple; each pixel of an output block is generated by choosing one of the two representative colours for that block, based on that block's bitmap.

In spite of its very simple mechanism, the algorithm yields surprisingly good results on photographic images, and it has the advantage of being very fast to decode with limited hardware. Although far surpassed in compression ratio by later block-transform coding methods such as JPEG, it had the advantage of very simple decompression and fast random access into the compressed image, and it can be regarded as a forerunner of modern texture compression algorithms.

References

1. ^ Campbell, G.; Defanti, T. A.; Frederiksen, J.; Joyce, S. A.; Leske, L. A. (1986). "Two bit/pixel full color encoding". Proceedings of the 13th annual conference on Computer graphics and interactive techniques - SIGGRAPH '86. pp. 215. doi:10.1145/15922.15910. ISBN 0897911962.  edit
2. ^ Wennersten, P.; Ström, J. (2009). "Table-based Alpha Compression". Computer Graphics Forum 28 (2): 687. doi:10.1111/j.1467-8659.2009.01409.x.  edit

See also

• Indexed color