Adaptive block truncation coding scheme using an edge following algorithm

B.T.C. (Block Truncation Coding) is a recent coding scheme for T.V. pictures producing compressed images with less than 2 bits/pixel. B.T.C. divides a picture into small blocks of fixed size : 4×4 pixels. The transmitter computes a two level representation of each block, preserving its local sample moments. Its essential artifact is that edges have tendency to be ragged. We thus propose a modified coding scheme based on statistical edge properties. An edge following algorithm is applied to the transmitted part of the picture. According to the position of edges in adjacent blocks to the transmitted one, a class of its pixels may be reconstructed by a third level issued from the mean of the block. Thus, our solution needs only few additional bits (0.18 bits/pixel) achieving fixed date rate of 2 bits/pixel.