High Performance Deartifacting Filters in Video Compression

1. High Performance Deartifacting Filters in Video Compression Renqi Zhang1, Yu Liu2, W.K.Cham1 1Department of Electronic Engineering,The Chinese University of Hong Kong 2Hong Kong Applied Science and Technology Research Institute (ASTRI) Abstract Artifacts commonly exist in the coded image and video. Non-local Kuan’s (NLK) filter has achieved the state-of-the-art performance on deartifacting the coded image, but there is no literature incorporating it into video scenarios. We propose two loop filters, quadtree-based NLK (QNLK) filter and quadtree-based overcomplete NLK (QOCNLK) filter, for video coding. In the proposed techniques, NLK and overcomplete NLK filters are used to restore quantized residual transform coefficients, and quadtree-based signaling strategy is used for adaptive filtering control. Experimental results show that the proposed techniques achieve significant bitrate saving and visual quality improvement, compared with H.264/AVC High Profile. _________________________________________________________________________________________________________________________________ Non-local Kuan’s Filter Consider the noise model: y=x+n, the quantized coefficient y0 and its neighboring coefficients yi, i=1,2,…,K from shifted blocks are the elements of the noisy signal y, so the corresponding original coefficients are x0 and xi, i=1,2,…,K. Kuan’s Filter: E[x]: ensemble mean; Cxy: covariance of x and y. Cy: auto-covariance of y. Parameters are estimated by non-local technique. The NLK and OCNLK Loop Filters 1. Pilot frame is the filtered result by the state-of-the-art method QALF+DLF. 2. The NLK filter is performed for each residual integer cosine transform (ICT) coefficient. We need the operation to obtain residual blocks. 3. OCNLK filter is the overcomplete extension of NLK. The Proposed QNLK and QOCNLK Filters Block selection Im,nis the block control to determine whether the current block uses the processed result by our filter. A quadtree structure is used to transmit Im,n: D: distortion between filtered frame and coded frame. R: bit for block control side information. λ: scaling factor. (u,v): frequency band index; Zm,n: normalizing factor; h: control the decay of exponential function. I frame P frame B frame Quadtree based block partition _________________________________________________________________________________________________________________________________ Experimental Results Experiments are implemented within KTA2.4r1 reference software.Benchmark: H.264 coded sequence. Bit rate reduction ΔBR(%) of CIF sequence by three Methods, compared with H.264 High Profile (a) H.264 coded frame (b) QALF+DLF filtered frame ˙QNLK and QOCNLK achieve on average 1.84% and 3.54% respectively, compared with QALF+DLF. ˙Picture visual quality is improved obviously as shown in the right figure. (c) QNLK filtered frame (b) QOCNLK filtered frame One coded frame of CIF sequence “Football” with QP=38