Progressive coding of error diffused images

We propose a new method to compress error diffused images with spatial scalability. This method is a kind of combination of inverse halftone and rehalftone. During inverse halftoning, we combine four dots into a pixel of a reduced image. Then, the reduced image is rehalftoned using an error diffusion algorithm. We encode an error diffused image progressively from the lowest resolution image to higher resolution image. To code higher resolution images, we use the dots in the previously coded lower resolution image. The compression ratios of the proposed algorithm are similar to those of the JBIG (Joint Bilevel Image Processing Group) progressive mode. However, the reduced image quality from the proposed algorithm is better than that from the JBIG progressive mode.