2008 年 37 巻 5 号 p. 702-709
In order to find an efficient lossy coding scheme of ordered dither images, two different coding categories, multi-level lossy image coding (LML) with post-processing of ordered dithering, and sending the number of black pixels in a block of bi-level pixels (BPN), are proposed and studied. Among the former category, we adopted JPEG2000 as the best one, and for the latter category, we assumed the context based coding, which refers to the numbers of black pixels in several neighboring blocks. By setting same bit rate per pixel for these two methods, the picture quality of the restored lossy bi-level images were evaluated using the PSNR of inverse halftoned images. It was found that to use the inverse halftoned (IH) image of lossless bi-level one as the reference image in calculating the PSNR will be better than to use the original multi-level image in reflecting the subjective picture quality, and that BPN has better performance than LML for higher bit rate and LML will catch up BPN as the bit rate decreases.
