Ying-zong Huang

Lloyd clustering of Gauss mixture models for image compression and classification

Abstract Gauss mixtures have gained popularity in statistics and statistical signal processing applications for a variety of reasons, including their ability to well approximate a large class of interesting densities and the availability of algorithms such as the Baum–Welch or expectation-maximization (EM) algorithm for constructing the models based on observed data. We here consider a quantization approach to Gauss mixture design based on the information theoretic view of Gaussian sources as a “worst case” for robust signal compression. Results in high-rate quantization theory suggest distortion measures suitable for Lloyd clustering of Gaussian components based on a training set of data. The approach provides a Gauss mixture model and an associated Gauss mixture vector quantizer which is locally robust. We describe the quantizer mismatch distortion and its relation to other distortion measures including the traditional squared error, the Kullback–Leibler (relative entropy) and minimum discrimination information, and the log-likehood distortions. The resulting Lloyd clustering algorithm is demonstrated by applications to image vector quantization, texture classification, and North Atlantic pipeline image classification.

Optimizing FEC Transmission Strategy for Minimizing Delay in Lossless Sequential Streaming

As cloud computing is taking off, the presence of high-performance interactive Internet applications is exploding. By nature, these applications require responsive client-server data exchange and lossless, in-order delivery. Previous work has shown that by using forward error correction (FEC), it is possible to reduce the data streaming latency caused by retransmissions of lost packets. However, the prior schemes only send FEC packets when there are no original packets pending transmission. In this paper, we further expand the hybrid FEC-ARQ protocol and show that sometimes, the transmission latency can be further reduced by preempting original data packets with FEC packets. We have formulated the decision of whether to send new original data packets, FEC packets, or resend original data packets as a transmission policy. An optimal transmission policy is selected to minimize the delay experienced by the application subject to a constraint on the amount of overhead. By using this optimal policy, we significantly improve the delay performance over straightforward FEC schemes while controlling the amount of overhead due to FEC.

Causal Transmission of Colored Source Frames over a Packet Erasure Channel

We propose a linear predictive quantization system for causally transmitting parallel sources with temporal memory (colored frames) over an erasure channel. By optimizing within this structure, we derive an achievability result in the high-rate limit and compare it to an upper bound on performance. The proposed system subsumes the well-known PCM and DPCM systems as special cases. While typically DPCM performs well without erasures and PCM suffers less with many erasures, we show that the proposed solution improves performance over both under all severities of erasures, with unbounded improvement in some cases.

A Joint Packet Selection/Omission and FEC System for Streaming Video

Media delivery over packet networks is often plagued by packet losses which limit its utility to end users. Forward error correction (FEC) based techniques are important for overcoming this problem. This paper further develops an FEC-based technique to maximize the expected received media quality by jointly choosing which packets to send and which packets to protect - including discarding packets to make additional room for protection. We describe a straight-forward implementation leveraging existing FEC system components. Comprehensive experiments demonstrate that significant gains in PSNR of several dB are achieved when sending H.264/MPEG-4 AVC coded video over a packet erasure channel.

Making Packet Erasures to Improve Quality of FEC-Protected Video

Media delivery over lossy packet networks is a challenging problem, and forward error correction (FEC) based techniques are an important technique for overcoming packet loss. Conventional FEC-based media delivery techniques protect all packets equally, or protect a subset of the packets, or protect different subsets of packets with different levels of protection, e.g., scalable coding with unequal error protection (UEP). This paper proposes an FEC-based technique to maximize the expected received media quality by explicitly discarding packets, when beneficial, in order to provide additional room for FEC. Given knowledge of the importance of each packet, we show that there is a simple and intuitive criterion for the optimal selection of which packets to discard and which to protect, as well as the level of protection, to minimize the expected distortion experienced at the receiver. The proposed approach provides significant gains over the conventional approaches, and these gains are illustrated for the case of sending H.264 coded video data over a packet erasure channel with known packet loss rate.

A class of compression systems with model-free encoding

Practical compression systems are constrained by their bit-stream standards, which define the source model together with the coding method used. We introduce a model-free coding architecture that separates the two aspects of compression and allows the design of potentially more powerful source models, as well as more flexible use of the compressed information stream. We show that this architecture is capable of producing competitive performance while supporting new use cases.

Minimizing delay in lossless sequential data streaming

There is an ongoing explosion of interactive Internet applications. By nature, these applications require responsive clientserver data exchange and lossless, in-order delivery. In previous work, we have shown that a hybrid FEC-ARQ protocol which combines sending original data packets with forward error correction (FEC) packets is effective in reducing the latency caused by retransmissions of lost packets. However, the prior scheme only sends FEC packets when there are no original packets pending transmission. In this paper, we further expand the investigation of the hybrid FEC-ARQ protocol and show that sometimes, the transmission latency can be further reduced by preempting original data packets with FEC packets. We have formulated the decision of whether to send new original data packets, FEC packets, or resend original data packets as a transmission policy. An optimal transmission policy is selected to minimize the delay experienced by the application subject to a constraint on the amount of waste. By using this optimal policy, we significantly improve the delay performance over straightforward FEC schemes while controlling the amount of waste due to FEC.

Separation architectures for lossy compression

High-performance Model-Code Separation (MCS) architectures for lossless compression are practically viable with graphical message-passing in the decoder. This paper extends separation architectures to lossy compression by constructing model-free but semantics-aware encoders and contributes a new inference-friendly low-density hashing quantizer (LDHQ) to support decoding.