Adaptively hybrid fractal image coding

• Published in: IET image processing Vol. 18; no. 7; pp. 1745 - 1758
• Main Authors: Wang, Qiang, Jin, Guohua, Bi, Sheng
• Format: Journal Article
• Language: English
• Published: Wiley 01.05.2024
• Subjects: fractals; image coding; image processing
• ISSN: 1751-9659; 1751-9667
• DOI: 10.1049/ipr2.13060

An adaptively hybrid method was proposed to improve the performance of fractal coding methods. First, it is found that the range blocks with large variances (RBLVs) play a crucial role in degrading decoded images, and the effect of the remaining range blocks with small variances (RBSVs) can be ignored. Then, an adaptive method was proposed to divide the range blocks into the above two categories: RBLVs and RBSVs. Second, RBLVs were designed to be encoded in an extended domain block pool (EDBP). Then, better block‐matching effect can be obtained, which will result in better decoded image quality. Further, the no‐search fractal encoding method is adopted for RBSVs to achieve faster encoding speed and fewer bits per pixel (bpp). Finally, four fractal coding methods were adopted to assess the performance of the proposed method. Experimental results show that compared with the previous methods, the PSNR quality of decoded images in the proposed method can be improved by about 0.15–0.4 dB, about 20%–35% of the total computations in encoding process can be saved, and about 0.2 bpp can be saved. Moreover, under the same decoding time, the proposed method can achieve comparable or smaller deviations regarding the decoded image. To improve the performance of the existing fractal coding methods, an adaptive method is proposed to divide the range blocks into two categories and adopted different encoding strategies for different types of range blocks. It can achieve better‐decoded image quality with faster encoding speed, fewer bits per pixel, and comparable decoding speed.