Jui-Chiu Chiang

Oversampled filter banks as error correcting codes: theory and impulse noise correction

Oversampled filter banks (OFBs) provide an overcomplete representation of their input signal. This paper describes how OFBs can be considered as error-correcting codes acting on real or complex sequences, very much like classical binary convolutional codes act on binary sequences. The structured redundancy introduced by OFBs in subband signals can be used to increase robustness to noise. In this paper, we define the notions of code subspace, syndrome, and parity-check polynomial matrix for OFBs. Furthermore, we derive generic expressions for projection-based decoding, suitable for the case when a simple second-order model completely characterizes the noise incurred by subband signals. We also develop a nonlinear hypotheses-test based decoding algorithm for the case when the noise in subbands is constituted by a Gaussian background noise and impulsive errors (a model that adequately describes the action of both quantization noise and transmission errors). Simulation results show that the algorithm effectively removes the effect of impulsive errors occurring with a probability of 10/sup -3/.

Region-of-interest based rate control scheme with flexible quality on demand

Conventional rate control schemes focus on making output bit rate approach a target value and are deficient in ensuring a higher quality of ROI (Region of Interest) than others in a frame. In this paper, we propose a new scheme for H.264/AVC, aiming to allocate more bit resource for the encoding of ROI and still maintain the accuracy of the output bit rate. ROI-based rate control algorithms can find their specific advantages in video telephony and video surveillance applications. Our proposed scheme is based on the one implemented in H.264/AVC JM software, but enhanced with several features: ROI determination with saliency map, tunable quality factor for ROI, two-channel (ROI & non-ROI) rate control, and QP adjustment with constraints from temporal and spatial domains, as well as from ROI/non-ROI adjacency boundaries. Experiment results show both advantages in objective PSNR and subjective evaluations for ROI, while making the output bit rate accurate as before.

A Fast H.264/AVC-Based Stereo Video Encoding Algorithm Based on Hierarchical Two-Stage Neural Classification

Stereo video, targeting at matching what the humans see in the real world, offers depth perception on observed scenes. The problem of compressing such a huge amount of video data has received considerable attention in the past few years. Its challenge comes from the much more complicated parameter selection (e.g., mode decision) process than single-channel video coding. To cope with this problem, the currently developed H.264/AVC-based JMVM platform is adopted here for implementation, where the encoding of the left-view channel is purely based on predictions from the temporal domain, while for the right-view channel, combined predictions from the temporal and the inter-view domains are exploited and a hierarchical two-stage neural classifier is designed for fast mode decision. The first-stage neural classifier determines candidates of block partition for each macroblock, while the second-stage classifier aims to choose the most probable prediction sources among the temporally forward/backward and inter-view directions. All input features for both stages of neural classifiers are calculated from simple inter-frame and inter-view analyses. In our scheme, the popular fast motion estimation schemes can be also cooperated for further speedup. Experiment results reveal that our proposed algorithm is capable of achieving up to 97% of time savings with nearly ignorable quality degradation and acceptable bit-rate increase (up to 5.67%).

Intelligent exposure determination for high quality HDR image generation

High dynamic range (HDR) image generation had been studied for years. Due to the expense and rareness of HDR cameras, many works try to generate HDR images using several low dynamic range (LDR) images with different exposure conditions. To ensure high-quality HDR image generation, details of the scene should be retained in different LDR images and the exposure parameters of LDR image should be chosen carefully. In this paper, we propose a technique to dynamically determine the suitable exposure parameter for LDR images according to the property of each scene to be captured. Experimental results reveal that better HDR images are always generated with the LDR images captured by the determined exposure, compared to those created by the method with fixed exposures.

Bit-depth scalable video coding using inter-layer prediction from high bit-depth layer

Scalable video coding (SVC) is currently developed as an extension of H.264/AVC video coding standard. In this paper, we propose three H.264/AVC compliant bit-depth scalable video coding schemes, named LH mode (Low Bit-depth to High Bit-depth), HL mode (High Bit-depth to Low Bit-depth) and combined LH-HL mode for different applications. All these schemes efficiently exploit the high correlation between the high bit-depth layer and the low bit-depth layer on Macroblock level. Experimental results indicate that the HL mode outperforms the other two schemes and it achieves up to 7 dB improvement over the simulcast where the high bit-depth video and low bit-depth representations are 12-bit and 8-bit, respectively.

Robust Video Transmission Over Mixed IP - Wireless Channels using Motion-Compensated Oversampled Filterbanks

Robust video coding has attracted increasing attention during the past few years. This paper proposes a joint source channel coding scheme able to resist transmission errors over mixed Internet-wireless channels. It involves motion-compensated oversampled filterbanks (OFBs). The redundancy introduced by the overcomplete representation in signals at the output of OFBs is employed for error correction of the motion compensated frames. The errors may be due to the wireless part of the channel (random noise), but also to the Internet part (packet losses). The performance of the proposed approach is illustrated for compressed streams transmitted through a packet erasure channel with an averaged packet loss of 6.25% followed by a binary symmetric channel with a crossover probability of 10-2

Block-based distributed video coding with variable block modes

In this paper, a new block-based pixel domain distributed video coding scheme featured with variable block modes is proposed. In addition to intra mode and Wyner-Ziv mode employed in conventional block-based distributed video coding scheme, two supplementary block modes “SKIP mode” and “zero motion mode” are introduced in the proposed scheme to improve the overall coding efficiency, as well as to reduce the decoding complexity. Moreover, the channel coding is performed on macroblcok level to reduce the coding loss due to inserted information in the parity bits. The simulation results show that the proposed scheme outperforms both the conventional frame-based transform-domain and the block-based pixel-domain distributed coding schemes.

A Hierarchical Two-Stage Neural-Classifier for Mode Decision of H. 264/AVC Stereo Video Encoding

This paper presents a design of H.264-based stereo video encoder. For our system, the currently developed JMVM platform is adopted, by which the encoding of the left-view channel is purely based on the predictions from the temporal domain, while for the right-view channel, combined predictions from the temporal/ disparity domains are exploited, with a hierarchical two-stage neural classifier for fast mode decision. The first-stage classifier determines promising candidates for variable block partition of each MB, while the second-stage classifier aims to choose the most probable prediction sources among the forward/backward motion and disparity frames. The input features for both stages of neural classifiers come from simple calculations on difference images between the currently coded frame and its reference frames. Experiment results indicate that the proposed algorithm can achieve up to 84% of time savings with nearly ignorable quality degradation and acceptable bit-rate increase (less than 7%).

Bit-depth scalable video coding with new inter-layer prediction

The rapid advances in the capture and display of high-dynamic range (HDR) image/video content make it imperative to develop efficient compression techniques to deal with the huge amounts of HDR data. Since HDR device is not yet popular for the moment, the compatibility problems should be considered when rendering HDR content on conventional display devices. To this end, in this study, we propose three H.264/AVC-based bit-depth scalable video-coding schemes, called the LH scheme (low bit-depth to high bit-depth), the HL scheme (high bit-depth to low bit-depth), and the combined LH-HL scheme, respectively. The schemes efficiently exploit the high correlation between the high and the low bit-depth layers on the macroblock (MB) level. Experimental results demonstrate that the HL scheme outperforms the other two schemes in some scenarios. Moreover, it achieves up to 7 dB improvement over the simulcast approach when the high and low bit-depth representations are 12 bits and 8 bits, respectively.

Motion-compensated oversampled filterbanks for robust video coding

During the past few years, much effort has been devoted for efficient coding of video. However, this high coding efficiency results in an increased sensitivity to transmission errors. This is the motivation for developing techniques allowing us altogether to transmit video sequences efficiently and to be robust to the transmission errors. This paper proposes a joint source-channel coding scheme using motion-compensated oversampled filterbanks (OFB). Previous work for robust transmission using OFB have concentrated on still images. Here, OFB are combined with motion compensation techniques. The redundancy introduced by the overcomplete representation is employed for error correction of the motion compensated frames. Experiments have shown that performance is acceptable even when the compressed stream is transmitted through a binary symmetric channel with crossover probability of 10/sup -2/.