面向对象分配带宽的极低比特率视频编码器

Very Low Bit-Rate Video Coder with Object-Oriented Bandwidth Allocation Technology

在低比特率环境下 ,如何提高图象编码质量是许多人感兴趣的课题 ,针对此问题 ,提出了一种面向对象分配带宽 (OOBA)的视频编码器 ,用以提高低比特率环境下编码图象的主观质量 ,在充分考虑人的主观视觉特性的基础上 ,该编码器把图象序列分成不同的视频对象 ,而每个对象以宏块为单位构成 ,并且对每个对象单独分配大小不同的带宽 ,以把更多的比特分配给主观感兴趣的对象 ,来达到在低比特率环境下提高编码图象主观视觉质量的目的 .虽然每个对象独立编码 ,但在比特流的组织上却能与 H.2 6 3兼容 .为了合理地在多个对象间分配带宽 ,还给出了基于速率 -失真 (R- D)模型、基于序列分析和比值加权法等 3种带宽分配方法 .实验结果表明 ,该编码器与传统的基于帧的编码器相比 ,在极低的速率下 ,峰值信噪比虽略有降低 ,但图象的主观视觉质量却得到较大的提高 .从而表明了该编码器的有效性 ,也说明在低比特率环境下 ,仅以客观准则作为评价编码器好坏的标准是不够的 .

How to improve the subjective visual quality of the video coded at low bit rate is an interested subject of many people. This paper proposes a video coding system based on object oriented bandwidth allocation(OOBA) technology to improve the subject quality of coded images. Exploiting human subjective visual characteristic sufficiently, this coder divides video sequence into multi video objects(VO) and allocates more bandwidth for the VO with more subjective significance to improve subjective quality of images coded at low bit rate. Each object is composed of macroblocks and coded separately. In bit stream context, the OOBA coder is compatible with H 263. For reasonable bandwidth allocation, present three schemes to allocate bandwidth for multi objects: rate distortion(R D) model based scheme ,sequence analysis based scheme and ratio weighting scheme. The result of experiments shows that the PSNR of OOBA coder is a little lower than that of frame based coder, but the subjective quality is much better. So, it proves the OOBA coder effective and indicates it is not enough to evaluate a video coder only with objective criterion such as PSNR .