Blocking Effect Reduction of DCT Coded Images Using AR Model

• Main Authors: Tseng, Chi-Ning, 曾紀寧
• Other Authors: Chang Ruey-Feng
• Format: Others
• Language: zh-TW
• Published: 1997
• Online Access: http://ndltd.ncl.edu.tw/handle/85355107394225795563

碩士 === 國立中正大學 === 資訊工程學系 === 85 === Digital images are more and more popular in our daily life and the demand of digital images has grown in the recent years. But the data sizes of digitalimages are usually large. In order to save the storage space and to reducethe transmission time, several techniques for image compression were developed.However, many annoying artifacts will appear in an image when the image is codedat lower bit rates. For example, the blocking effects will be visible along the block boundaries, the ringing effects will appear around the sharp edges,and the staircase noise will arise on the skew edges. Traditionally, low-pass filters are used to reduce blocking effects. Though the blocking effectsare reduced by low-pass filters, the details of the images such as edges aredegraded at the same time. In this thesis, a new post- processing approach isproposed to reduce blocking effects and preserve image details.Our approach consists of three main procedures, segmentation, filtering withAR model coefficients, and 1-D filtering. The input image is first segmentedinto several non-overlapping regions. The pixels within the same region havesimilar gray levels and the edges in the original image appear as region boundaries. Auto=regressive (AR) model coefficients for each region are extracted by the two- dimensional linear analysis. The model coefficientsfor a region can reflect the characteristics of this region. Therefore, the filter with these model coefficients is then adopted to reduce the blockingeffects and preserve the characteristics within this region. The above procedures work iteratively to get better performance. This iterative methodcan also reduce the ringing effects around the sharp edges. At last, 1-Dfilters along the skew edges are used to reduce the staircase noise.The proposed approach is tested on several images. The results are comparedwith the low-pass filter by the peak signal-to-noise (PSNR) ratio criterion.The experimental results demonstrate that a significant improvement in subjective and objective quality is achieved. This shows the feasibility ofthe proposed approach.