The importance of visual communications has increased tremendously in the couple of decades as the saying goes “a picture worth thousand words”. Emerging applications such as video-conferencing, cellular video-telephones and multimedia will have a great impact on nowadays professional life, education and entertainment .The digital representation of visual information in its canonic form generates a huge amount of data. It creates three problems:
- Storage Space
- Transmission
- Manipulation
Digital image compression is the solution to the above problems. Image compression is aimed to minimize the number of bits needed to represent an image without sacrificing quality.
In general, compression can be divided into two broad classes:
- Lossless
- Lossy
In lossless compression, no information is lost, hence, there is no distortion. However we can get low compression ratios, typically 2 or 3 are achieved in practice.
In lossy compression, data redundancies as well as data which are not noticeable to human visual systems are discarded. This produces some distortions. Hence there is trade-off between image quality and compression.
Joint Photographic Expert Group (JPEG) is the one compression expert group. In JPEG compression, the grayscale image is first partitioned into 8x8 blocks that are independently transformed using block Discrete Cosine Transform (DCT), then quantized and entropy coded. JPEG introduces blocking artifacts at medium and high compressions because of its short and nonoverlapping basis functions [1]. JPEG also suffers from ringing artifacts at high compression. Both artifacts are clearly visible at high compression. JPEG2000 is a new generation technique, which can encode images at very low bit-rate with acceptable quality. Because its coder is based on wavelet transform, there will be some ringing artifacts in the reconstructed image. JPEG-2000 outperforms JPEG in terms of compression as well as quality. However, ringing artifacts of images are still a main bottleneck in the JPEG 2000 coding standard. In this paper we have analyzed the effect of different DWT resolutions for ringing artifacts with the same compression.
Rest of the paper is organized is as follows. In section 2, JPEG-2000 is briefly discussed. In section 3, ringing artifacts and its problem are discussed. In section 4, DWT is presented very briefly. Simulation results are presented in section 5. Finally, conclusion is given in section 6.
JPEG-2000
Recently, wavelet transforms have attracted considerable attention with their application to image coding [2]. It is also the transformation technique in JPEG-2000. JPEG-2000 has a long list of features, a subset of which is [3].
- State-of-the-art low bit-rate compression performance
- Progressive transmission by quality, resolution, component, or spatial locality
- Lossy and lossless compression (with lossless decompression available naturally through all types of progression)
- Random (spatial) access to the bitstream
- Region of interest coding by progression
- Continuous and bi-level compressions