Lossy Coding of Error Diffused Images — Comparison of multi-level image based method and bi-level image based method —

The lossy coding scheme of error diffused images is an interesting topic but has not been well studied yet. In this paper we study two different categories. First one is to use lossy multi-level image coding methods such as JPEG, JPEG- LS and JPEG2000 with post-processing of error diffusion. The other category is lossy coding of bi-level data by sending the number of black pixels in plural pixels. Among the former category, we found that JPEG2000 performs best, and in the latter category, we chose the simplest case of sending the number of black pixels in successive two pixels. The quality of the pictures of these two methods at the same bit-rate was compared using the SNR of inversed halftone images to the original multi-level image. It was found that the first category works better for the low frequency dominated images and works worse for the high frequency dominated images.