Woo-jin Han

Performance improvement of wavelet-based scalable video coder based on pre-decoder side rate-distortion optimization

In wavelet-based scalable video coding, the encoder generates one large bit-stream and the pre-decoder can truncate it to have an arbitrary size by using the embedding principle. Most conventional rate control algorithms utilize some information available only at the encoder, thus, it cannot be applied directly in the scalable video coders since the actual bit allocation should be performed after the encoding phase. We modify the rate-distortion (R-D) function and propose a new rate control algorithm based on the modified R-D function, which uses only the pre-decoder side information. In addition, since large PSNR variation results in noticeable visual artifacts at low PSNR frames, we propose a novel distortion flattening technique to reduce the variance of PSNR curve and to improve the performance of low PSNR frames. Experimental results have shown that the both proposed methods improved the average PSNR, and especially, the proposed distortion flattening technique makes the visual quality more consistent.

New MCTF method based on adaptive direction of motion vector for interframe wavelet coding

With recent growth of multimedia applications for delivering compressed bitstream over networks, scalability has become an important feature in video coding. The interframe wavelet coding (IWC) inherently provides temporal resolution, spatial resolution, and SNR scalability through wavelet transform and embedded quantization. In this paper, we propose a new motion compensated temporal filtering (MCTF) method. This method adaptively changes the directions for motion compensation in a group-of-pictures (GOP). Three modes are selected for the directions of motion estimation based on a criterion using motion information at boundary area in image sequence. This proposed method is composed of two parts. The first part is the extraction of motion information at boundary area. The second part is to process temporal filtering according to the selected direction for motion estimation. Simulation results show that the proposed method outperforms the conventional IWC method by 0.4 1.0 dB.

Wavelet scalable video coding with minimal average temporal distance for motion estimation

Wavelet scalable video coding (WSVC) can be used efficiently for scalable mesh compression for virtual reality applications over IP networks. This paper proposes efficient methods to improve the coding efficiency of WSVC through the minimization of average temporal distance (ATD) for motion estimation. The ATD is closely related to the peak signal-to-noise ratio (PSNR) performance of WSVC which is based on motion compensated temporal filtering. Simulation results show that the proposed methods with minimum ATD give about 1 to 2dB PSNR improvements compared to the conventional WSVC.