关键词: 图像增强, 离散余弦变换, 块状效应, 低通滤波

Abstract: For the sake of efficient storage and transmission, more and more images are compressed, thus compressed domain image enhancement techniques are attracting more and more attention. This paper illustrates the background of Discrete Cosine Transform（DCT） domain color image enhancement techniques. Among these algorithms, they often suffer from blocking artifact around the boundaries of image blocks. The blocking artifact reason of recently published Color Image Enhancement by Scaling（CES） algorithm is analyzed, and then two improved methods are proposed to suppress the blocking artifact. Simulation results show that the improved methods can not only perform well in suppressing blocking artifact, but also can decrease the computation complexity.

Key words: image enhancement, DCT（Discrete Cosine Transform）, blocking artifact, LPF（Low-Pass Filtering）