Skipping Selected Steps of DWT Computation in Lossless JPEG 2000 for Improved Bitrates

TL;DR

This paper proposes a modified DWT approach for lossless JPEG 2000 that skips certain steps to improve bitrates, especially for non-photographic images, with minimal impact on compression time.

Contribution

It introduces a heuristic-based SS-DWT method that adapts skipping steps for better compression, compliant with JPEG 2000 standards, and demonstrates significant bitrate improvements.

Findings

Average bitrate improvement of roughly 5% across test images.

Non-photographic images see about 14% bitrate reduction.

Enhanced method achieves up to 17.5% bitrate improvement for non-photographic images.

Abstract

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.