Adaptive transform coding of four-color printed images

In contrast to transform image coding concepts for television signals published so far, this paper aims to report on the design of a coder for 4-color images which are to be printed e.g. in magazines: First the major differences in picture material compared to TV-signals are pointed out. Then a highly adaptive threshold coding structure is introduced which is able to make-up for the greatly varying image content encountered. This structure is described by adaptation to the local image content, quantization and coding of the supra-threshold coefficients using Huffman-code, and methods to code the position of the supra-threshold coefficients. Then it is shown, how a second transform in the spatial domain can be employed to decorrelate the color-components. Finally the problems when attempting multiple coding of images are sketched.