时 间：2012年6月12日（周二）上午 9:30

地 点：北京大学计算机科学技术研究所 309 会议室 （中关村北大街128号计算机所大楼）

报告一

报告人：蓝善祯

报告题目：Robust Image Coding Based Upon Compressive Sensing

报告摘要：

Multiple description coding (MDC) is one of the widely used mechanisms to combat packet-loss in non-feedback systems. However, the number of descriptions in the existing MDC schemes is very small (typically 2). With the number of descriptions increasing, the coding complexity increases drastically and many decoders would be required. In this paper, the compressive sensing (CS) principles are studied and an alternative coding paradigm with a number of descriptions is proposed based upon CS for high packet loss transmission. Two-dimensional discrete wavelet transform (DWT) is applied for sparse representation. Unlike the typical wavelet coders (e.g., JPEG 2000), DWT coefficients here are not directly encoded, but resampled towards equal importance of information instead. At the decoder side, by fully exploiting the intra-scale and inter-scale correlation of multiscale DWT, two different CS recovery algorithms are developed for the low-frequency subband and high-frequency subbands,respectively. The recovery quality only depends on the number of received CS measurements (not on which of the measurements that are received). Experimental results show that the proposed CS-based codec is much more robust against lossy channels, while achieving higher rate-distortion (R-D) performance compared with conventional wavelet-based MDC methods and relevant existing CS-based coding schemes.

注：文章选自 IEEE Trans. on Multimedia, Vol.14, No.2, April 2012

报告二

报 告 人：周同

报告题目：Quality Assessment of Asymmetric Stereo Video Coding

报告摘要：

It is well known that the human visual system can perceive high frequencies in 3D, even if that information is present in only one of the views. Therefore, the best 3D stereo quality may be achieved by asymmetric coding where the reference (right) and auxiliary (left) views are coded at unequal PSNR. However,the questions of what should be the level of this asymmetry and whether asymmetry should be achieved by spatial resolution reduction or SNR (quality) reduction are open issues. Extensive subjective tests indicate that when the reference view is encoded at sufficiently high quality, the auxiliary view can be encoded above a low-quality threshold without a noticeable degradation on the perceived stereo video quality. This low-quality threshold may depend on the 3D display; e.g., it is about 31 dB for a parallax barrier display and 33 dB for a polarized projection display. Subjective tests show that, above this PSNR threshold value, users prefer SNR reduction over spatial resolution reduction on both parallax barrier and polarized projection displays. It is also observed that, if the auxiliary view is encoded below this threshold value, symmetric coding starts to perform better than asymmetric coding in terms of perceived 3D video quality.

注：文章选自 IEEE ICIP 2010