Development of Efficient Algorithms for JPEG2000 Image Coder

Abstract

Compression of digital images has been a topic of research for many years and a number of image compression standards have been developed for different applications. The role of compression is to reduce bandwidth requirements for transmission and memory requirements for storage of all forms of data. Although, developments on technology front provide high speed digital communication and large memories, image compression is still of major importance. The advances in technologies generally result into increased demand for image communication, as well as demand for higher quality image printing and display. The work presented in this thesis revolves around the improvements in the JPEG2000 image compression standard. We have proposed an Edge Adaptive Wavelet Lifting Scheme that deals with the edges present in an image efficiently. In this approach, the lifting direction is not restricted to horizontal and/or vertical direction only, but other lifting directions are also used if the edges present in an image are neither in horizontal nor in vertical direction. This approach represents the decomposed image more efficiently because there are less number of wavelet coefficients having large magnitude in the high pass subbands. Due to this approach, the energy of high pass subbands decreases and these subbands are represented more efficiently. It has been observed that proposed scheme improves PSNR by more than 4 dB when compared with the JPEG2000 lifting scheme. Tile boundary artifacts in JPEG2000 compressed images have also been discussed in this thesis. We have proposed a post-processing technique to reduce tile boundary artifacts in JPEG2000 compressed images in this work. This technique reduces tile boundary artifacts which occur in an image when it is compressed at low bit rate using JPEG2000 standard. We have analyzed the effect of quantization on the region of the tile boundaries of JPEG2000 compressed images.