Lossless chain coder for gray edge images

This paper proposes an efficient method for lossless coding of gray level edge images, which are frequently used in image processing. The method consists of analyzing the edge image in connected sets of pixels by means of chain coding as a function of its starting points, their relative intensities and their displacements within these sets. In order to avoid the redundant information a DPCM coder is used. Then the pixel intensities, the costly information, are coded by an arithmetic encoder, and the rest (coordinates, displacements and movements) by a Huffman encoder, which is less demanding in terms of hardware and software than the first one. For this type of images, the proposed method provides lossless compression rates higher than the commonly used lossless methods. Results show that the proposed method can provide for this type of images 20-78% better compression when compared with the best available methods, and 19% better compression when compared with JPEG-LS (arithmetic version).