  In order to improve bitrates of lossless JPEG 2000, we propose to modify the
discrete wavelet transform (DWT) by skipping selected steps of its computation.
We employ a heuristic to construct the skipped steps DWT (SS-DWT) in an
image-adaptive way and define fixed SS-DWT variants. For a large and diverse
set of images, we find that SS-DWT significantly improves bitrates of
non-photographic images. From a practical standpoint, the most interesting
results are obtained by applying entropy estimation of coding effects for
selecting among the fixed SS-DWT variants. This way we get the compression
scheme that, as opposed to the general SS-DWT case, is compliant with the JPEG
2000 part 2 standard. It provides average bitrate improvement of roughly 5% for
the entire test-set, whereas the overall compression time becomes only 3%
greater than that of the unmodified JPEG 2000. Bitrates of photographic and
non-photographic images are improved by roughly 0.5% and 14%, respectively. At
a significantly increased cost of exploiting a heuristic, selecting the steps
to be skipped based on the actual bitrate instead of an estimated one, and by
applying reversible denoising and lifting steps to SS-DWT, we have attained
greater bitrate improvements of up to about 17.5% for non-photographic images.
