适用于分布式视频编码框架的整数离散余弦变换算法

Integer discrete cosine transform algorithm for distributed video coding framework

鉴于H.264的整数离散余弦变换(DCT)算法及其量化方法复杂度高,难以直接应用于分布式视频编码(DVC)框架的现状,提出了一种基于大跨度定长(步长为2的正整数次方)量化的整数DCT算法及变换基生成方法。该算法充分地利用整数DCT基的可伸缩特性寻找最迎合硬件工作原理的变换基,在保证"小"变换基的同时将编码器的伸缩量化阶段"转移"到解码器一端以降低编码器复杂度。在"转移"过程中,该算法利用DCT系数饱和放大保证图像质量,利用DCT系数的溢出上限保证算法的可靠性,通过减小基偏差提高压缩性能。实验结果表明,与H.264对应模块相比,该算法的量化方式便于位平面提取,在图像质量达到准无损压缩的前提下将编码器的伸缩量化阶段的运算量缩减至16次整型常量加法运算,图像质量与压缩率的性价比提升了23.9%,适用于分布式编码框架。

Now the integer Discrete Cosine Transform （DCT） algorithm of H. 264 can not apply to Distributed Video Coding （DVC） framework directly because of it＇s high complexity. In view of this, the authors presented a integer DCT algorithm and transform radix generating method based on fixed long step quantization which length was 2x （x was a plus integer）. The transform radix in H. 264 could be stretched. The authors took full advantage of this feature to find transform radix which best suits for working principle of hardware, and it moved the contracted-quantized stage from coder to decoder to reduced complexity of coder under the premise of ＂small＂ transform radix. In the process of ＂moving＂, this algorithm guaranteed image quality by saturated amplification for DCT coefficient, guaranteed reliability by overflow upper limit, and improved compression performance by reducing radix error. The experimental results show that, compared with corresponding module in H. 264, the quantization method of this algorithm is convenient for bit-plane extraction. And it reduces calculating work of eontracted-quantized stage of coder to 16 times of integer constant addition under the premise of quasi-lossless compression, raises the ratio of image quality and compression by 0.239. This algorithm conforms to DVC framework.