| ¡¡ | Chinese Journal of Computers Full Text |
| Title | Improving Cross Trace-Based Algorithm for Fractal Image Coding |
| Authors | HE Chuan-Jiang SHEN Xiao-Na |
| Address | (College of Mathematics and Physics, Chongqing University, Chongqing 400030) |
| Year | 2007 |
| Issue | No.12(2156¡ª2163) |
| Abstract & Background | Abstract The excellent visual quality and high compression rate of fractal image coding have the limited applications due to exhaustive inherent encoding time. The time is mostly spent on searching for the best-matched block to an input range block in a usually large domain pool; therefore, a fast algorithm is proposed to limit the search space in this paper. It is an improvement of the algorithm based on cross trace proposed by this first author; in detail, the newly-defined cross trace of image block (i.e., the sum of absolute intensities of normalized block along the main and sub-principal diagonal pixels), which is a modification of original one, is utilized to confine efficiently the search space to the vicinity of the initial-matched block (i.e., the domain block having the closest new cross trace to that of the input range block being encoded). Moreover, an error threshold is also used to control the search neighborhood around the initial-matched block. The proposed algorithm has been compared with the fast algorithm based on cross-trace experimentally, showing it performs better in terms of encoding time and image quality. keywords image compression; fractal; iterated function system; fractal image coding; cross trace background Over the past decade, fractal image coding has not only been attracting extensive attention of the researchers in the field of image compression, but also received a lot of interests from the researchers in other areas of image processing. The technique can provide a high decoded image quality at a high compression ratio; however, the problem with fractal coding is the highly computational complexity in the encoding process. The time to fractally encode an image is mostly spent on finding the best-matched block to an input range block in a large domain pool. Therefore, focal aims of fractal image coding are to accelerate the encoding process, in which many efforts have been attempted to accelerate the encoding process since the early 1990s. However, most of the existing accelerating schemes reduce significantly the required computation only at the expense of more or less degradation of the reconstructed image quality. The proposed algorithm, which is an improvement of the fractal algorithm based on cross trace proposed by this first author £ÛHe C, Huang X. Fast fractal image coding based on local cross trace. Chinese Journal of Computers£¬ 2005, No.10£Ý, can considerably shorten the encoding time, while achieving the same or better decoded image quality as baseline fractal algorithm with full search. The major research interests of this group are fractal image coding, PDE-based image processing, and so on. The topic in this paper is primarily a part of Ph.D. dissertation, entitled "Study on Algorithms for Fractal Image Coding Technology", by the first author. In this Ph.D. dissertation, the author has explored many aspects of fractal image coding, and then improved some existing fractal encoding/decoding algorithms and proposed several new fractal encoding/decoding algorithms. Most of these algorithms have been published, respectively, in IEE Electronics Letters (2004, No.2, No.17), IEE Proc.-Vision Image and Signal Processing (2004, No.3), Chaos, Solitons & Fractals (2006, No.5; 2007, No.4), Acta Electronica Sinica (2004, No.11), Chinese Journal of Computers (2005, No.10) and Journal of Image and Graphics (2004, No.9; 2005, No.5; 2006, No.12), etc. |