Lossy coding of ordered dither images -- Comparison of dispersed dither and clusterd dither --

The lossy compression performance of two different ordering schemes: dispersed dither type and clustered dither type, are studied and compared. For lossy coding of ordered dither images, two methods; multi-level lossy image coding (LML) with post-processing of ordered dithering and transmission of the number of black pixels in a block of bi-level pixels (BPN), with two kind of bit rates, corresponding to two block sizes (2 times 2 pixels and 4 times 4 pixels) are examined. Concerning dither types, not much difference was found in entropy and also in image quality for 4 times 4 lossy case, but Bayer dithering works slightly better than screen dithering for 2 times 2 cases. Concerning the comparison of LML and BPN, BPN shows subjectively better picture quality than LML in 2 times 2 cases and the PSNR of Inverse Halftone (IH) images of restored bi-level images to the IH images of lossless halftone images is found to well reflect the subjective impression.