Perceptual quality metric for digital video coding

A new perceptually significant block-edge impairment metric as a quantitative distortion measure for blocking artifacts in digital video coding is presented. This distortion metric does not require the original image sequence as a comparative reference, and is found to be consistent with subjective evaluation.     

Region-based video coding using mathematical morphology

This paper presents a region-based coding algorithm for video sequences. The coding approach involves a time-recursive segmentation relying on the pixels homogeneity, a region-based motion estimation, and motion compensated contour and texture coding. This algorithm is mainly devoted to very low bit rate video coding applications. One of the important features of the approach is that no assumption is made about the sequence content. Moreover the algorithm structure leads to a scalable coding process giving various levels of quality and bit rates. The coding as well as the segmentation are controlled to regulate the bit stream. Finally, the interest of morphological tools in the content of region-based coding is extensively reviewed     

Efficient multi-view video coding using inter-view information

Multi-view video coding (MVC) has been extended from H.264/AVC to improve the coding efficiency of multi-view video. This paper proposes a fast mode decision algorithm which can make an early decision on the correct mode partition to solve the issue of the enormous computational complexity. The best modes of the reference views are utilized to determine the complexity of the macroblock (MB) in the current view, the mode candidates needed to be calculated can then be obtained according to the complexity. If the complexity is low or medium, the search range can be reduced. The threshold of the rate-distortion cost for the current MB is calculated using the co-located and neighboring MBs in previously coded view and is utilized as the criterion for early termination. The motion vector difference in the reference view is applied to dynamically adjust the search range in the current MB. Experimental results prove that the proposed algorithm achieves a time saving of 81.05% for a fast TZ search and 87.85% for full search, and still maintains quality performance and bitrate.     

Flash scene video coding using weighted prediction

A novel algorithm for coding flash scenes is proposed. In principle, flash scenes can be detected by analyzing the histogram differences between frames. The proposed algorithm then suggests an adaptive coding order technique for increasing the efficiency of video coding by taking account of characteristics of flash scenes in video contents. The use of adaptive coding technique also benefits to enhance the accuracy of derived motion vectors for determination of weighting parameter sets. Experimental results show that a significant improvement of coding performance in terms of bitrate and PSNR can be achieved in comparison with the conventional weighted prediction algorithms.     

Independent key frame coding using correlated pixels in distributed video coding

A novel intra-coding technique is proposed that eliminates the requirement of a secondary coding scheme for coding the key frames in distributed video coding (DVC). The proposed technique uses the Slepian-Wolf theorem and Wyner-Ziv (WZ) coding with spatially predicted information to transmit the key-frames to the DVC decoder. Simulation results show that the proposed WZ-intra coding technique (WZ-I) can achieve up to 5 dB PSNR gain compared to MPEG-2 intra coding (MPEG-I) at the same bit rate with negligible computational cost to the encoder     

Asymmetrical principal component analysis for video coding

Principal component analysis (PCA) can be used to encode video sequences at extremely low bit rates, e.g. 34.6 dB (PSNR) at 4.2 kbit/s. The same eigenvectors are used for encoding and decoding for this coding. Introduced is a coding scheme where eigenvectors for only part of the video frames are used for encoding but the eigenvectors for the entire frame are used for decoding. This is called asymmetric PCA coding. This reduces the complexity of encoding by ap5 times and at the same time increases the reconstruction quality for the facial part of the video with 0.4 dB (PSNR)..     

Fast Intra prediction algorithm for quality scalable video coding

The coding efficiency of currently scalable video coding is very high at the cost of high coding complexity. Therefore, it is extremely important to improve the coding speed. By making use of the advantage of the quality scalable video coding (QSVC) structure, we propose a new fast Intra coding algorithm for QSVC. Based on the coding structure of QSVC, temporal, spatial and inter-layer correlations are employed together to predict candidate macro-block (MB) modes and their encoding orders to exclude low possible modes, and then three new early termination methods are proposed. In addition to MB modes, temporal, spatial and inter-layer correlations are also adopted together to estimate weight values and orders of all directional modes. Experimental results demonstrate that the coding speed of the proposed algorithm can be improved by 63.58 % in average with negligible coding loss.     

Scalable wavelet video coding using aliasing-reduced hierarchicalmotion compensation

We describe a spatially scalable video coding framework in which motion correspondences between successive video frames are exploited in the wavelet transform domain. The basic motivation for our coder is that motion fields are typically smooth and, therefore, can be efficiently captured through a multiresolutional framework. A wavelet decomposition is applied to each video frame and the coefficients at each level are predicted from the coarser level through backward motion compensation. To remove the aliasing effects caused by downsampling in the transform, a special interpolation filter is designed with the weighted aliasing energy as part of the optimization goal, and motion estimation is carried out with low pass filtering and interpolation in the estimation loop. Further, to achieve robust motion estimation against quantization noise, we propose a novel backward/forward hybrid motion compensation scheme, and a tree structured dynamic programming algorithm to optimize the backward/forward mode choices. A novel adaptive quantization scheme is applied to code the motion predicted residue wavelet coefficients, Experimental results reveal 0.3-2-dB increase in coded PSNR at low bit rates over the state-of-the-art H.263 standard with all enhancement modes enabled, and similar improvements over MPEG-2 at high bit rates, with a considerable improvement in subjective reconstruction quality, while simultaneously supporting a scalable representation.     

Perceptual stereoscopic video coding using disparity just-noticeable-distortion model

In this paper, we propose perceptual stereoscopic video coding using a disparity just-noticeable-distortion (JND) model. We obtain the disparity JND model in stereo videos by disparity masking effects of the human visual system (HVS). The disparity JND model represents the maximum distortion of stereo perception that HVS cannot perceive. Based on the disparity JND model, we adjust prediction residuals to remove the perceptual redundancy of stereo videos. Thus, we achieve significant bit-rate saving while maintaining visual quality. Experimental results demonstrate that the proposed method significantly improves coding efficiency without loss of stereoscopic perceptual quality.     

Energy-efficient video streaming over Bluetooth using rateless coding

Energy-efficient error control for IEEE 802.15.1 (Bluetooth) video communication is proposed. The scheme is based on block-oriented incremental redundancy provided by rateless coding and receiver feedback. Results are presented for time-sensitive video streaming applications under a Markovian channel model. When the proposed algorithm is compared to variations of Bluetooth forward error control, there are improvements of around 3 dB in received video quality and of over 10% in energy efficiency.     

Fairness-oriented multi-stream rate adaptation using scalable video coding

In the delivery of video services like video on-demand, IP-TV, sport broadcasting, as well as real-time streaming, the end-user expectation is to receive the best feasible quality independently of the particular video complexity, even in the presence of packet losses. In this scenario, rate adaptation is required to optimize the overall quality, whereas fairness is an important issue that has to be addressed. In this paper we propose a multi-stream rate adaptation framework with reference to the scalable video coding (SVC) extension of the H.264/AVC standard with medium grain scalability (MGS). We first define a general discrete multi-objective problem with the aim to maximize the sum of assigned rates, while minimizing the differences among the expected distortions, under a total bit-rate constraint. A single-objective problem formulation is then derived by applying a continuous relaxation. Finally, a simplified continuous semi-analytical model that accurately estimates the rate–distortion relationship for both error-free channel and packet-erasure channel is also proposed, which allows us to derive an optimal and low-complexity procedure to solve the relaxed problem. Unequal erasure protection (UXP) is also considered and designed to suitably shape the rate–distortion relationship for different values of RTP packet-loss rate. The numerical results show the goodness of our framework in terms of error gap between the relaxed and its related discrete solution, and the significant performance improvement achieved with respect to an equal-rate adaptation scheme.     

Low bit-rate video coding using wavelet vector quantisation

A method for low bit-rate video coding based on wavelet vector quantisation is proposed. Motion estimation/compensation using overlapped block matching (OBM) is employed to eliminate the blocking effects in the prediction error introduced by conventional block matching. It is shown that OBM significantly increases the efficiency of the wavelet transform coder. The motion-compensated interframe prediction error is decomposed using a wavelet transform and a method is employed for the efficient coding of the wavelet coefficients. In this technique, the coefficients are coded with a zero-tree multistage lattice vector quantiser. Simulation results are provided to evaluate the coding performance of the described coding scheme for low bit-rate video coding. It provides constant bit rate, obviating the need for buffer, with just small fluctuations in PSNR. Moreover, comparison with the RM8 implementation of the standard H261 video coder shows that the presented codec provides improvements in both peak signal-to-noise ratio and picture quality     

Efficiency analysis of multihypothesis motion-compensatedprediction for video coding

Overlapped block motion compensation or B-frames are examples of multihypothesis motion compensation where several motion-compensated signals are superimposed to reduce the bit-rate of a video codec. This paper extends the wide-sense stationary theory of motion-compensated prediction (MCP) for hybrid video codecs to multihypothesis motion compensation. The power spectrum of the prediction error is related to the displacement error probability density functions (pdfs) of an arbitrary number of hypotheses in a closed-form expression. We then study the influence of motion compensation accuracy on the efficiency of multihypothesis motion compensation as well as the influence of the residual noise level and the gain from optimal combination of N hypotheses. For the noise-free limiting case, doubling the number of (equally good) hypotheses can yield a gain of up to 1/2 bits/sample, while doubling the accuracy of motion compensation can additionally reduce the bit-rate by up to 1 bit/sample independent of N. For realistic noise levels, it is shown that the introduction of B-frames or overlapped block motion compensation can provide larger gains than doubling motion compensation accuracy. Spatial filtering of the motion-compensated candidate signals becomes less important if more hypotheses are combined. The critical accuracy beyond which the gain due to more accurate motion compensation is small moves to larger displacement error variances with increasing noise and increasing number of hypotheses N. Hence, sub-pel accurate motion compensation becomes less important with multihypothesis MCP. The theoretical insights are confirmed by experimental results for overlapped block motion compensation, B-frames, and multiframe motion-compensated prediction with up to eight hypotheses from ten previous frames.     

Spatial quality index based rate perceptual-distortion optimization for video coding

Spatial Quality Index (SQI) is a recently proposed video quality assessment metric that can predict video quality much close to subjective judgments. Since current video coding still has much redundancy in the sense of visual perception, in this paper, we incorporate SQI into video coding to further improve compression ratio without visual quality loss. Firstly, contributions of different human visual system (HVS) properties used in SQI are analyzed. Then two most important HVS properties, i.e. contrast masking effect (CME) and motion masking effect (MME), are extracted to measure perceptual-distortion D_p in video coding. Finally, based on D_p, a rate perceptual-distortion optimization (RpDO) algorithm is presented by adopting a suitable Lagrange multiplier from previous study. Experimental results show that, RpDO can averagely achieve 14% bitrate reduction when compared to HM14.0 under the same visual quality. At the same time, there is no significant change in the encoding time.     

Three-dimensional wavelet transform video coding using symmetriccodebook vector quantization

A new vector quantizer codebook design for video compression is described. This uses the notion that symmetries in the data, which are seldom captured exactly in any training dataset, are important perceptually and lead to a more robust codebook. The method is illustrated using three-dimensional (3-D) wavelet transformed video sequences.     

Very low-bit-rate segmentation-based video coding using contour andtexture prediction

The most efficient video coding standard for low bit rates (around 64 kb/s) is the H.261 algorithm recommended by ITU-TS. However, in certain applications such as mobile audiovisual communications and videophone through PSTN, the available transmission bandwidth is very limited. Therefore codecs working at very low bit rates are required. The paper presents a segmentation-based video coding algorithm that can work at rates as low as 10 kb/s. A novel representation of the contour information using a number of control points is proposed to estimate the contour shapes and locations from the previous frame by using the motion information. The texture parameters are also predicted and only the residual values are entropy coded. In addition two novel postprocessing techniques for edge-profile smoothing and jagged-edge rectification are described     

Prediction of stereoscopic video quality using objective quality models of 2-D video

The timely deployment of three-dimensional (3-D) video applications requires accurate objective quality measures, so that time consuming subjective tests can be avoided. Investigated is the correlation between subjective and objective evaluations of colour plus depth map 3-D video. Subjective tests are performed to determine the overall image quality and depth perception of a range of asymmetrically coded video sequences. The subjective results are used to determine more accurate objective quality assessment metrics for colour plus depth map based stereoscopic video.     

Lagrange multiplier selection in wavelet-based scalable video coding for quality scalability

In this paper, a method for Lagrange multiplier selection is proposed in the context of rate-distortion optimisation for wavelet-based scalable video coding targeting quality scalability. Despite the prevalence of the conventional method for Lagrange multiplier selection in hybrid video coding, the underlying formulation is not applicable to wavelet-based scalable video coding. To address the inherent challenges, a thorough analysis of the rate-distortion models for transform video coding is provided with regard to low and middle-to-high bit-rates, respectively. Based on the analysis, the models are consolidated according to experimental observations and the consolidated rate-distortion models serve as the basis for the derivation of the Lagrange multiplier. Considering the influence of the open-loop prediction structure on the rate-distortion performance, the Lagrange multiplier is initially derived for a single-targeted bit-rate. Moreover, the method for Lagrange multiplier selection in scalable video coding aiming at multiple-targeted bit-rates is proposed in a general sense of bit-rate range, varying from low to high bit-rates, building on the initially derived Lagrange multiplier for a single-targeted bit-rate. The proposed Lagrange multiplier is content adaptive and well suited for wavelet-based scalable video coding where quantisation steps are unavailable. Detailed performance evaluation of the proposed method for wavelet-based scalable video coding is provided with regard to a given targeted bit-rate and multiple-targeted bit-rates, respectively. The experimental results have demonstrated the effectiveness of the proposed Lagrange multiplier for rate-distortion optimisation considering quality scalability in wavelet-based scalable video coding.