Reduction of blocking artifact in block-coded images using wavelet transform

We propose a simple yet efficient method which reduces the blocking artifact in block-coded images by using a wavelet transform. An image is considered as a set of one-dimensional signals, and so all processing including the wavelet transform are one-dimensionally executed. The artifact reduction operation is applied to only the neighborhood of each block boundary in the wavelet transform at the first and second scales. The key idea behind the method is to remove the blocking component which reveals stepwise discontinuities at block boundaries. Each block boundary is classified into one of shade region, smooth edge region, and step edge region. Threshold values for the classification are selected adaptively according to each coded image. The performance is evaluated for 512/spl times/512 images JPEG coded with 30:1 and 40:1 compression ratios. Experimental results show that the proposed method yields not only a PSNR improvement of about 0.69-1.06 dB, but also a subjective quality nearly free of the blocking artifact and edge blur.