Journal:Informatica
Volume 24, Issue 4 (2013), pp. 657–675
Abstract
In this paper, a modified version of the discrete wavelet transform (DWT), distinguishing itself with visibly improved space localization properties and noticeably extended potential capabilities, is proposed. The key point of this proposal is the full decorrelation of wavelet coefficients across the lower scales. This proposal can be applied to any DWT of higher orders (Le Gall, Daubechies D4, CDF 9/7, etc.). To open up new areas of practical applicability of the modified DWT, a novel exceptionally fast algorithm for computing the DWT spectra of the selected signal (image) blocks is presented. In parallel, some considerations and experimental results concerning the energy compaction property of the modified DWT are discussed.
Journal:Informatica
Volume 18, Issue 3 (2007), pp. 463–478
Abstract
Fractal image compression is an engaging and worthwhile technology that may be successfully applied to still image coding, especially at high compression ratios. Unfortunately, the large amount of computation needed for the image compression (encoding) stage is a major obstacle that needs to be overcome. In spite of numerous and many-sided attempts to accelerate fractal image compression times, the “speed problem” is far from being carried to its conclusion.
In the paper, a new version (strategy) of the fractal image encoding technique, adapted to process bi-level (black and white) images, is presented. The strategy employs the necessary image similarity condition based on the use of invariant image parameters (image smoothness indices, image coloration ratios, etc.). It is shown that no images can be similar (in the mean squared error sense) if their respective parameter values differ more than somewhat. In the strategy proposed, the necessary image similarity condition plays a key role – it is applied to speed-up the search process for optimal pairings (range block-domain block), i.e., it enables to narrow the domain pool (search region) for each range block. Experimental analysis results show that implementation of the new fractal image encoding strategy accelerates bi-level image compression times considerably. Exceptionally good results (compression times and quality of restored images) are obtained for silhouette images.
Journal:Informatica
Volume 15, Issue 3 (2004), pp. 411–424
Abstract
The contribution of this paper is a new version of the escape time algorithm adapted to synthesize fractal images, identified with attractors of iterated function systems (IFS). The proposed synthesis algorithm is based on the use of shift dynamics, associated with one or another IFS. The novelty of the algorithm is grounded on two factors. Firstly, the strategy for the separation of extended domains of the inverse affine transformations, specified by IFS, is developed. Secondly, the variable escape time for different points of a synthesized fractal image (IFS attractor) is proposed and explored. Experimental results show that the above two factors ensure uniform rendering of image points (pixels) in colour.