Lossless image compression algorithms for continuous-tone images have received a great deal of attention in recent years. However, reports on benchmarking their performance have been limited. In this paper, we present a comparative study of the following algorithms: UNIX compress, gzip, LZW, Group 3, Group 4, JBIG, old lossless JPEG, JPEG-LS based on LOCO, CALIC, FELICS, transform, and PNG. The test images consist of two sets of eight bits/pixel continuous-tone images: one set contains nine pictorial images, and another set contains eight document images, obtained from the standard set of CCITT images that were scanned and printed using eight bits/pixel at 200 dpi. In cases where the algorithm under consideration could only be applied to binary data, the bitplanes of the gray scale image were decomposed, with and without Gray encoding, and the compression was applied to individual bit planes. The results show that the best compression is obtained using the CALIC and JPEG–LS algorithms. © 2002 SPIE and IS&T.