Color image compression by moment-preserving and block truncation coding techniques

A new color image compression technique based on moment-preserving and block truncation coding (BTC) is proposed. An input image is divided into non-overlapping blocks. And each block is coded by two representative colors, or equivalently, by two sets of tristimulus values (R₁, G₁, B₁) and (R₂, G₂, B₂). To compute the two representative colors of each block, some color moments of the block are preserved, and the two sets of desired tristimulus values are computed accordingly using analytic formulas. The compression ratio is 6 when the block size is 4×4. Furthermore, a simple method is applied to quantize the bit map into 64 predefined bit maps and requantize each color component from 8 bits into 4 bits. An average compression ratio of 14.00 can be achieved