DATA-COMPRESSION OF HALF-TONE IMAGES BY PERIODIC ERROR DIFFUSION METHOD

The recent expansion of facsimile application fields has increased the need to transmit at high speed not only black and white binary images for characters, but also half-tone images including high quality photographic images. This paper proposes the periodic error diffusion method for realizing high quality half-tone images with highly efficient coding availability. This method has a high expression ability for both gray scale and resolution, and also moire patterns are not likely to occur for screened photographs input. In addition, this method realizes a high coding efficiency, because the half-tone thresholded data by applying this method has a periodic characteristic. This paper also proposes the adaptive coding preprocessing method for thresholded mixed images including both characters and half-tone images. The coding efficiency for mixed image is thus improved.