Ya-Qin Zhang

A deblocking algorithm for JPEG compressed images using overcomplete wavelet representations

This paper introduces a new approach to deblocking of JPEG compressed images using overcomplete wavelet representations. By exploiting cross-scale correlations among wavelet coefficients, edge information in the JPEG compressed images is extracted and protected, while blocky noise in the smooth background regions is smoothed out in the wavelet domain. Compared with the iterative methods reported in the literature, our simple wavelet-based method has much lower computational complexity, yet it is capable of achieving the same peak signal-to-noise ratio (PSNR) improvement as the best iterative method and giving visually very pleasing images as well.

A comparative study of DCT- and wavelet-based image coding

We undertake a study of the performance difference of the discrete cosine transform (DCT) and the wavelet transform for both image and video coding, while comparing other aspects of the coding system on an equal footing based on the state-of-the-art coding techniques. The studies reveal that, for still images, the wavelet transform outperforms the DCT typically by the order of about 1 dB in peak signal-to-noise ratio. For video coding, the advantage of wavelet schemes is less obvious. We believe that the image and video compression algorithm should be addressed from the overall system viewpoint: quantization, entropy coding, and the complex interplay among elements of the coding system are more important than spending all the efforts on optimizing the transform.

Scalable video transport over wireless IP networks

There has been great interest in transporting real-time video over wireless IP networks from both industry and academia. Real-time video applications have quality-of-service (QoS) requirements. However, the fluctuations of wireless channel conditions pose many challenges to providing QoS for video transmission over wireless IP networks. It has been shown that scalable video coding and adaptive services are viable solutions under a time-varying wireless environment. We propose an adaptive framework to support quality video communication over wireless IP networks. The adaptive framework includes: (1) scalable video representations, (2) network-aware video applications, and (3) adaptive services. Under this framework, as wireless channel conditions change, the mobile terminal and network elements can scale the video streams and transport the scaled video streams to receivers with acceptable perceptual quality. The key advantages of the adaptive framework are: (1) perceptual quality is degraded gracefully under severe channel conditions; (2) network resources are efficiently utilized; and (3) the resources are shared in a fair manner.

MPEG4 compressed video over the Internet

This paper focuses on transport issues of MPEG-4 video over the Internet. Specifically, we present a packetization algorithm for MPEG-4 bit streams at the sync layer and an end-to-end feedback control mechanism. Our packetization algorithm achieves both efficiency and robustness by exploiting the unique video object plane (VOP) feature in MPEG-4 while our feedback control algorithm is capable of estimating available network bandwidth based on the packet loss information at the receiver. Simulation results demonstrate that once our algorithms are employed by an adaptive MPEG-4 encoder, MPEG-4 video is able to achieve good perceptual picture quality at the receiver under low bit rate and varying network conditions and efficiently utilize network resources.

Network bandwidth sharing for transporting rate-adaptive packet video using feedback

This paper presents a framework for network bandwidth sharing to transport rate-adaptive packet video using feedback. We show how a weight-based bandwidth sharing policy can be used to allocate network bandwidth among competing video connections and design a feedback control algorithm using the available bit rate (ABR) flow control mechanism. A novel video source rate adaptation algorithm is introduced to decouple a video sources actual transmission rate from the rate used for the protocol convergence. We also demonstrate how an on-line minimum rate renegotiation and weight adjustment mechanisms can be employed to further enhance the flexibility of our feedback control protocol.

Adaptive QOS control for MPEG-4 video communication over wireless channels

This paper proposes an adaptive quality-of-service (QoS) control to increase the robustness of MPEG-4 video communication over wireless channels. More specifically, the proposed adaptive QoS control consists of optimal mode selection and delay-constrained hybrid automatic repeat request (ARQ). The optimal mode selection is employed to provide QoS support on the compression layer while delay-constrained hybrid ARQ is used to provide QoS support on the link layer. Simulation results show that the proposed adaptive QoS control achieves satisfactory quality for MPEG-4 video under dynamically changing wireless channel conditions and utilizes network resources efficiently.

A comparative study of DCT and wavelet based coding

We study the performance difference of the discrete cosine transform (DCT) and the wavelet transform for both image and video coding, while comparing other aspects of the coding system on an equal footing. Based on the state-of-the-art coding techniques, we point out that, for still images, wavelet outperforms DCT with a coding gain of about one dB in PSNR. For video coding, the advantage of wavelet schemes is less obvious. We believe that image and video compression algorithms should be addressed from the overall system viewpoint. Quantization, entropy coding, and paying attention to details are more important than spending all the efforts on optimizing the transform.

A simple deblocking algorithm for JPEG compressed images using overcomplete wavelet representations

This paper introduces a new approach to deblocking of JPEG compressed images using overcomplete wavelet representations. By exploiting cross-scale correlations among wavelet coefficients, edge information in the JPEG compressed images is extracted and protected, while blocky noise in the smooth background regions is smoothed out in the wavelet domain. Compared with the iterative methods reported in the literature, our simple wavelet-based method has much lower computational complexity, yet it is capable of achieving the same PSNR improvement as the best iterative method, and giving visually very pleasing images as well.

Jitter smoothing and traffic modeling for MPEG‐2 video transport over ATM networks

In this article, we study how to deal with jitter when a variable‐bit‐rate (VBR) MPEG‐2 video is delivered through asynchronous transfer mode (ATM) networks. First, the MPEG‐2 system and its timing model are reviewed and difficulties introduced by ATM cell delay jitter are elucidated. Second, approaches to smoothing network jitter for both constant‐bit‐rate and VBR traffic are reviewed. A novel approach to modeling the end‐to‐end MPEG‐2 packet generation and arrival process in the presence of network jitter is next presented. Based on this model, the buffer behavior of the MPEG‐2 transport stream system target decoder is simulated. Simulation results show that jitter significantly affects the required decoder buffer size and packet loss ratio.

Optimal mode selection in Internet video communication: an end-to-end approach

We present an end-to-end approach to generalize the classical theory of rate distortion (R-D) optimized mode selection for point-to-point video communication. We introduce a notion of global distortion by taking into consideration of both the path characteristics and the receiver behavior, in addition to the source behavior. We derive, for the first time, a set of accurate global distortion metrics for any packetization scheme. Equipped with the global distortion metrics, we design an R-D optimized mode selection algorithm to provide the best trade-off between compression efficiency and error resilience. As an application, we integrate our theory with point-to-point MPEG-4 video conferencing over the Internet. Simulation results conclusively demonstrate that our end-to-end approach offers superior performance over the classical approach for Internet video conferencing.