Guobin Shen

Transcoder with arbitrarily resizing capability

This paper presents a transcoding technique that possesses the capability of arbitrarily resizing. Arbitrarily resizing is necessary when the resolution of an end display device differs from that of the video being pre-encoded. It is also a good strategy to achieve better visual quality when the transmission bandwidth is limited. The two key steps for a superior transcoding are the resizing and the coding steps. The resizing is achieved through an upsampling-filtering-downsampling process. Several motion vector reuse strategies that the specially tailored for the transcoder with arbitrarily resizing capability are presented. Experimental results confirm that the resizing can yield better visual quality.

Arbitrarily shaped transform coding based on a new padding technique

Coding of arbitrarily shaped image segments is an important tool to achieve object-based coding, which is becoming more and more popular in todays multimedia applications. We introduce a new padding technique based on which the arbitrarily shaped DCT can be implemented using a normal N/spl times/N DCT. The new padding is carried out for each arbitrarily shaped block in such a way that there are as many transformed coefficients of high frequencies as possible that could be set to zero. In the best case, it does not expand the data set in the DCT-domain. Arbitrarily shaped DCT coding based on this padding technique is developed, and then analyzed and compared against some of the existing algorithms in terms of the rate-distortion performance, computational complexity, and implementation cost.

New predictive diamond search algorithm for block-based motion estimation

In this paper a new fast motion estimation algorithm is presented. The algorithm, named as Predictive Diamond Search, is actually based on the Diamond Search (DS) algorithm, which was recently adopted inside the MPEG-4 standard. The DS algorithm, even though faster than most known algorithms, was found not to be very robust in terms of quality for several sequences. By introducing a new predictive criterion and some additional steps in DS, our simulation results show that the proposed algorithm manages to have similar complexity with the DS algorithm, while having superior and more robust quality, similar to that of the Full Search algorithm.

An advanced zonal block based algorithm for motion estimation

Efficient motion estimation is very important for compressing video in standards like MPEG1/2/4 and ITU-T H.261/263. In this paper a new algorithm is presented which can outperform most of the traditional fast motion estimation algorithms in both speed and quality. In addition, in some cases this algorithm can achieve even better visual quality, than the “optimal” but computational intensive “full search” algorithm.

A new padding technique for coding of arbitrarily-shaped image/video segments

Object-based coding is becoming more and more important in todays multimedia applications. Shape-adaptive DCT (SA-DCT) provides a useful tool for coding of arbitrarily-shaped image/video segments which is indispensable to achieve object-based coding. In this paper, we introduce a new padding technique based on which the arbitrarily-shaped DCT can be implemented using normal N×N DCT. The new padding is carried out for each arbitrarily-shaped block in such a way that the number of non-zero coefficients after DCT is guaranteed to be no more than that of the original image data, thereby never expanding the data set in the DCT-domain. Arbitrarily-shaped DCT coding based on this padding technique is developed, and then analyzed and compared against some of the existing algorithms in terms of rate-distortion performance, computational complexity, and implementation cost.

Fast and efficient motion estimation using diamond zonal-based algorithms

Motion estimation has always been an important part of video encoding systems because it can reduce temporal redundancy effectively and thus has significant impact on the bit rate and the output visual quality of the encoded sequence. Unfortunately, when using the brute-force full search algorithm, motion estimation consumes a very large portion of the encoding time. Previously, several algorithms have been proposed which try to reduce complexity, usually, with a significant loss in visual quality. Based on the diamond zonal search framework we introduced recently, we propose in this paper a novel algorithm called advanced diamond zonal search (ADZS), which was submitted to and well received by the Moving Pictures Experts Group (MPEG) standard committee for possible inclusion as an encoder optimization tool. ADZS was criticized in MPEG for using fixed thresholds, which may not be suitable for all video sequences. To address this issue, we further propose a threshold-adaptive version called threshold-adaptive advanced diamond zonal search (TAADZS). Simulation results verify the superior performance of ADZS and TAADZS over other fast algorithms and the robustness of TAADZS over ADZS.

An efficient hybrid arbitrarily-shaped object coding technique

In this paper, we present a very efficient shape-adaptive coding method which is a hybrid between the standard SA-DCT and the padding technique we proposed in our early work [1999]. This hybrid has led to a significantly lower computation burden while the coding performance is improved. This conclusion is proved by thorough complexity analysis and extensive simulation. This method also has the shape preserving property and exhibits asymmetric complexities between the encoder and the decoder.

Syntax-constrained rate-distortion optimization for DCT-based image encoding methods

In this paper, we presented a novel and effective optimization method to achieve better trade-off between rate and distortion. The optimization is done at the encoder side alone and is transparent to the decoder. That is the quantized DCT coefficient set it optimized with full syntax compliance and decoder compatibility. The proposed method determines both the positions and the retained values of quantized DCT coefficients according to the rate-distortion performance measured by the associating Lagrangian cost. Fast dynamic programming technique was developed to release the computation burden. All the experiments show that the proposed method consistently outperforms other existing optimization methods.

Achieving optimal rate-distortion performance in arbitrarily-shaped transform coding

In this paper, we present a simple but effective method to enhance the coding performance of shape-adaptive DCT (SA-DCT). By choosing the first processing direction (between horizontal and vertical) within each boundary block for doing the 1D transform, the proposed method guarantees to achieve optimal rate-distortion results and actually outperforms the existing SA-DCT algorithms significantly. The proposed method is also applicable to arbitrarily-shaped coding based on some padding techniques.

Rate-distortion optimization for arbitrarily-shaped object coding

The trade-off between rate and distortion suggests two approaches for the rate-distortion optimization: (1) reduce the rate at a smaller increase in distortion (pushing the rate-distortion curve to the left) and (2) reduce the distortion at a smaller increase in rate (pushing the rate-distortion curve downward). In general, only the first approach is applicable for ordinary fully-defined blocks of square size, which is the case in all existing image/video coding standards other than MPEG-4. The authors show that for arbitrarily-shaped video objects, the inner object blocks can be optimized in the same way; while the boundary blocks (of arbitrary shapes), if padded properly, can be optimized using not only the first approach but also the second approach as well. To circumvent the high computational complexity, fully embedded pattern tables are designed so that the most computationally expensive part can be replaced by relatively simple table searching operations. Extensive simulation have been done and the results are found to support the conclusion drawn.