分块离散余旋变换压缩图像的一种统一后处理算法.pdf

Unified Artifacts Reduction for Block DCT Compressed 1 Images * Zhai Guangtao, Xu Yi , Yang Xiaokang, Zhang Wenjun, Yu Songyu Institute of Image Communication and Information Processing, Shanghai Jiao Tong University, Shanghai, China (200240) Abstract We propose a unified scheme to alleviate the blocking, ringing and blurring artifacts in block DCT compressed images. The image is decomposed into 2 levels using the over-complete wavelet transform, and the wavelet coefficients are filtered with consideration of local image properties. For the smooth region, the wavelet coefficients are averaged over the range of blocking artifacts’ extension in the over- complete wavelet transform domain on respective levels. For the texture region, only the coefficients on the first level are averaged to prevent over-smooth of the image. And for the edge region, the coefficients are first smoothed and then high-pass filtered to enhance the edges so as to restrain the ringing and blurring artifacts. The inverse transform of the filtered coefficients is performed towards the quality enhanced image. And a quantization constraint is imposed on the final result for better PSNR and visual performance. Keywords: Image postprocessing, Deblocking, Overcomplete Wavelet Expansion 1. INTRODUCTION Nowadays the Block-based DCT (BDCT) is the most widely used compression technique for image (JPEG) and video sequence (MPEG[1], h.26x[2]). The block-wise DCT