A novel block truncation coding of color images using a quaternion-moment-preserving principle

Block truncation coding (ETC) is an efficient tool for image compression, To compress color-pixel blocks, a novel color ETC algorithm, called quaternion-moment block truncation coding (QMBTC), is presented in this paper, Analytical formulas for QMBTC, whose computation time is on the order of pixel block size, are derived by using quaternion arithmetic and the moment-preserving principle, The proposed color ETC algorithm can adaptively truncate a pixel block into one or two output classes according to the distribution of color values inside the blocks, The experimental results show that the compression ratio is increased as compared with existing color ETC algorithms, and the picture quality of reconstructed images is satisfactory, In addition, a post-ETC data compression scheme is proposed to further compress the subimage constructed by reproduction colors of truncated pixel blocks, Using a lookup table to display decoded data, this postprocessing scheme can output images acceptable to human eyes.