Rate distortion optimization can significantly improve encoder performance in most video coding applications. Taking MPEG-2 as an example, this paper addresses the full rate distortion optimization for the first time by searching the product space of all four free parameters regardless of the computational complexity. An efficient graph-based searching algorithm was extended to the MPEG-2 video coding case from the authors' previous work to find the optimal coefficient indices in the optimization process. The proposed full rate distortion optimization algorithm serves the important role of providing an upper-bound benchmark without considering frame dependence and quantization weight matrix optimization. Two approximations of the full rate distortion optimization algorithms are also presented in order to reduce the computational complexity with a gradual degradation of the rate distortion performance. On average, 2~3dB gain is achieved with the proposed algorithms compared to regular MPEG-2 encoder.

This paper proposes two entropy constrained color splitting algorithms through building a binary tree structure for a progressive transmission of palette images. At each step of color splitting, a representative color is split into two new representative colors to minimize the distortion incurred by the reconstructed image subject to an entropy constraint. Among the bit rates of interest, both of the proposed unconditional entropy constrained color splitting algorithms and the conditional entropy constrained color splitting algorithm achieve, on average, 20% more size reduction than the existing distortion-based color splitting algorithm while maintaining the same distortion for our tested images. The superiority of the proposed algorithms is observed for color-quantized nature images and for synthetic images. Furthermore, all the proposed algorithms have a very moderate complexity and can be applied into practical applications like Web browsing through wireless or dialup links.

To maximize rate distortion performance while remaining faithful to the JPEG syntax, the joint optimization of the Huffman tables, quantization step sizes, and DCT indices of a JPEG encoder is investigated. Given Huffman tables and quantization step sizes, an efficient graph-based algorithm is first proposed to find the optimal DCT indices in the form of run-size pairs. Based on this graph-based algorithm, an iterative algorithm is then presented to jointly optimize run-length coding, Huffman coding, and quantization table selection. The proposed iterative algorithm not only results in a compressed bitstream completely compatible with existing JPEG and MPEG decoders, but is also computationally efficient. Furthermore, when tested over standard test images, it achieves the best JPEG compression results, to the extent that its own JPEG compression performance even exceeds the quoted PSNR results of some state-of-the-art wavelet-based image coders such as Shapiro's embedded zerotree wavelet algorithm at the common bit rates under comparison. Both the graph-based algorithm and the iterative algorithm can be applied to application areas such as web image acceleration, digital camera image compression, MPEG frame optimization, and transcoding, etc.

JPEG optimization strives to maximize the best rate distortion performance while remaining faithful to the JPEG syntax. Given an image, if soft decision quantization (SDQ) is applied to its DCT coefficients, then Huffman table, quantization step sizes and SDQ coefficients are three free parameters over which a JPEG encoder can optimize. In this paper, we first propose a novel algorithm to find the optimal SDQ coefficient indices in the form of run-size pairs among all possible candidates given that the other two parameters are fixed. Based on this algorithm, we then formulate an iterative algorithm to jointly optimize the run-length coding, Huffman coding and quantization step sizes. The proposed iterative algorithm achieves a compression performance better than any previously known JPEG compression results and even exceeds the quoted PSNR results of some state-of-the-art wavelet-based image coders like Shapiro's embedded zerotree wavelet algorithm at the common bit rates under comparison.

This paper introduces a sub-band adaptive algorithm that avoids the signal path delay, and so can be used in an adaptive active control (feedback) system. A side effect of this algorithm is that it still causes extra delay in the error path due to the analysis filter bank. Even though the delay along the error path has only a slight influence on the steady-state behavior, it does decrease the system bounds of stability. We propose an error path delay compensation method that alleviates this problem. Simulation results are presented to illustrate the efficiency of the new adaptive algorithm.