BTC Image Coding Using Median Filter Roots

In this paper we source encode the truncated block used in block truncation coding. It is shown that the truncated block is well approximated by wide-sense Markoff statistics; a signal having these characteristics has a high probability of belonging to the root signal set of median filters. Because the root signal space is much smaller than the binary space, it takes fewer bits to specify the truncated block in the root signal space, obtaining in this manner rate compression. Using two-dimensional filtering we can reduce the standard BTC rate of 1.63 bits/pel to 1.31 bits/pel. Using one-dimensional filtering along with a trellis encoder, rates close to 1.1 bits/pel are obtained with this fixed-length coding method.