甚低比特率水下视频图像压缩编码方法

为满足水声信道有限带宽的要求,提出了一种高效的水下视频图像压缩编码方案。编码系统主要由图像预处理、帧内编码和帧间预测编码3个模块组成。基于小波变换的预处理模块用于去除水下图像中的视觉冗余。根据水下图像的特点,采用基于小波树的WDR(wavelet difference reduction)算法对帧内图像进行高效编码。帧间运动估计和补偿是针对预处理后的图像子带进行,运动补偿后的残差图像采用基于重要子块和重要系数的双重WDR编码策略。实验结果表明:在保证图像重建质量的前提下,本文算法的平均压缩比可以达到250∶1～500∶1,基本满足水声信道传输速率为16 Kbps时的要求。     

H.263: video coding for low-bit-rate communication

This article provides an overview of H.263, the new ITU-T Recommendation for low-bit-rate video communication. H.263 specifies a coded representation for compressing the moving picture component of audio-visual signals at low bit rates. The basic structure of the video source coding algorithm is taken from ITU-T Recommendation H.261 and is a hybrid of interpicture prediction to reduce temporal redundancy and transform coding of the prediction residual to reduce spatial redundancy. The source coder can operate on five standardized picture formats: sub-QCIF, QCIF, CIF, 4CIF, and 16CIF. The decoder has motion compensation capability with half-pixel precision, in contrast to H.261 which uses full-pixel precision and employs a loop filter. H.263 includes four negotiable coding options which provide improved coding efficiency: unrestricted motion vectors, syntax-based arithmetic coding, advanced prediction, and PB-frames     

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.     

Very low bit-rate video coding using variable block-sizeentropy-constrained residual vector quantizers

We present a practical video coding algorithm for use at very low bit rates. For efficient coding at very low bit rates, it is important to intelligently allocate bits within a frame, and so a powerful variable-rate algorithm is required. We use vector quantization to encode the motion-compensated residue signal in an H.263-like framework. For a given complexity, it is well understood that structured vector quantizers perform better than unstructured and unconstrained vector quantizers. A combination of structured vector quantizers is used in our work to encode the video sequences. The proposed codec is a multistage residual vector quantizer, with transform vector quantizers in the initial stages. The transform-VQ captures the low-frequency information, using only a small portion of the bit budget, while the later stage residual VQ captures the high-frequency information, using the remaining bits. We used a strategy to adaptively refine only areas of high activity, using recursive decomposition and selective refinement in the later stages. An entropy constraint was used to modify the codebooks to allow better entropy coding of the indexes. We evaluate the performance of the proposed codec, and compare this data with the performance of the H.263-based codec. Experimental results show that the proposed codec delivered significantly better perceptual quality along with better quantitative performance     

Low-bit-rate video coding using dense motion field and uncoveredbackground prediction

It is well known that accurate dense motion field can improve the video coding efficiency. This paper presents a novel Markov random field (MRF) model that estimates both the dense motion and uncovered background fields in image sequences, and the application of these estimates in H.263-based video coding framework.     

Very low bit-rate video coding with DFD segmentation

A video coding system for applications requiring very low bit-rate is presented. This coding scheme uses an intraframe coder for the initial frame in the video sequence and subsequent frames are coded using an interframe coding method. A wavelet-based technique is used for intraframe coding. For interframe coding, displaced frame differences (DFD) are computed and coded using a segmentation-based method wherein the displaced frame difference is segmented into active and inactive regions using morphological operators. To meet the very low bit-rate requirements, the motion vectors are processed so as to reduce their contribution to the overall bit-rate. To reduce coding artifacts, a post-processing technique is developed for use at the decoder. Coding performance of the proposed coding scheme is evaluated at 16 kbit/s and 32 kbit/s using luminance component of several typical test sequences at QCIF resolution with a frame rate 8.3 frame/s.     

In-loop selective processing for contour artefact reduction in video coding

Proposed is an in-loop decontouring algorithm that utilises block-based processing for video coding. In order to avoid uniform filtering that brings about unnecessary processing, candidate blocks that may contain noticeable false contours using different kinds of features in a block are sequentially refined. Then, pseudorandom noise masking is applied to them to reduce contour artefacts. It is demonstrated that visual quality could be efficiently improved with a negligible rate-distortion (RD) loss.     

Fractal coding of video sequence using circular prediction mappingand noncontractive interframe mapping

We propose a novel algorithm for fractal video sequence coding, based on the circular prediction mapping and the noncontractive interframe mapping. The proposed algorithm can effectively exploit the temporal correlation in real image sequences, since each range block is approximated by the domain block in the adjacent frame, which is of the same size as the range block. The computer simulation results demonstrate that the proposed algorithm provides very promising performance at low bit rate, ranging from 40-250 kbyte/s.     

Allowing content-based functionalities in segmentation-based coding schemes

This paper deals with the use of the segmentation tools and principles presented in [10] and [13] for allowing content-based functionalities. In this framework, means for supervised selection of objects in the scene are proposed. In addition, a technique for object tracking in the context of segmentation-based video coding is presented. The technique is independent of the type of segmentation approach used in the coding scheme. The algorithm relies on a double partition of the image that yields spatially homogeneous regions. This double partition permits to obtain the position and shape of the previous object in the current image while computing the projected partition. In order to demonstrate the potentialities of this algorithm, it is applied in a specific coding scheme so that content-based functionalities, such as selective coding, are allowed.     

Boundary filter optimization for segmentation-based subband coding

This paper presents boundary optimization techniques for the nonexpansive decomposition of arbitrary-length signals with multirate filterbanks. Both biorthogonal and paraunitary filterbanks are considered. The paper shows how matching moments and orthonormality can be imposed as additional conditions during the boundary filter optimization process. It provides direct solutions to the problem of finding good boundary filters for the following cases: (a) biorthogonal boundary filters with exactly matching moments and (b) orthonormal boundary filters with almost matching moments. With the proposed methods, numerical optimization is only needed if orthonormality and exactly matching moments are demanded. The proposed direct solutions are applicable to systems with a large number of subbands and/or very long filter impulse responses. Design examples show that the methods allow the design of boundary filters with good frequency selectivity     

Constant quality video coding using video content analysis

In the literature, several rate control techniques have been proposed to aim at the optimal quality of digitally encoded video under given bit budget, channel rate and buffer size constraints. Typically, these approaches are group-of-picture (GOP) based. For longer, heterogeneous sequences, they become unacceptably complex or struggle with model mismatches. In this paper, an off-line segment-based rate control approach is proposed for controlling the distortion variation across successive shots of a video sequence when encoding with single-layer (MPEG-4 baseline, MPEG-4 AVC) and scalable (wavelet) video codecs. Consistent quality is achieved by optimally distributing the available bits among the different segments, based on efficient rate-distortion (R-D) modelling of each segment. The individual segments are defined based on shot segmentation and activity analysis techniques. The algorithm is formulated for three different distribution models: download, progressive download and streaming. The results indicate that the proposed technique improves the quality consistency significantly, while the processing overhead compared to classical two-pass variable bit-rate (VBR) encoding is limited.     

基于帧内帧间联合预测的深度视频编码方法

在基于多视点加深度(MVD)格式的视频编码方案中,深度视频的编码性能直接影响最终绘制的虚拟视点的质量。对于具有边界的深度块而言,传统的帧内预测和帧间预测模式仍存在一定的提升空间。因此,文中提出一种基于帧内帧间联合预测的深度视频编码方法。该方法首先获取当前深度块的最优帧内预测模式和最优帧间预测模式。然后,将这两种模式应用于边界深度块的不同区域。最后,自适应地调整预测结果的加权系数,实现联合预测。实验结果表明,相对于3D-HEVC平台的传统预测模式,本方法实现了更好的编码性能。     

Novel prediction schemes for error resilient video coding

A conventional video codec uses encoder reconstruction of previous frames for motion compensated prediction. This is designed to minimize the encoder prediction error and assumes error free transmission. In this paper we use a modified prediction mechanism both at the encoder and decoder and propose techniques to improve the error resilience of H.264/AVC when transmitted over error prone networks. In our schemes we provide greater emphasis on Intra pixels during the formation of the reference frame used for prediction, thereby achieving better resilience. We also incorporate leaky prediction to further improve the robustness. We apply leaky prediction selectively at a macroblock level based on a simple mean square error metric in order to reduce the bit-rate penalty. Substantial performance gains have been observed in simulations. The effectiveness of using leaky prediction can be observed in medium and fast moving video sequences.     

Efficient view-temporal prediction structures for multi-view video coding

To compress multi-view video, spatial redundancy between adjacent view sequences as well as temporal redundancy need to be eliminated. View-temporal prediction structures are proposed, which can be adjusted to various characteristics of multi-view videos. The proposed prediction structure achieves better coding performance than the reference prediction structure for the standardisation of multi-view video coding.     

Objective quality evaluation for low-bit-rate speech coding systems

An LPC (linear predictive coding) cepstrum distance measure (CD) is introduced as an objective measure for estimating the subjective quality of speech signals. Good correspondence between LPC CD and the subjective quality, expressed in terms of both opinion equivalent Q and mean opinion score, are shown. Good repeatability of objective quality evaluation using LPC CD is also shown. A method for generating an artificial voice signal that reflects the characteristics of real speech signals is described. The LPC CD values calculated using this artificial voice are almost the same as those calculated using real speech signals. The speaker-dependency of the coded-speech quality is shown to be an important factor in low-bit-rate speech coding. Even taking this factor into consideration, LPC CD is shown to be effective for estimating the subjective quality     

分割基图像编码算法中基于结构的标识提取方法

提出了一种新的基于结构的标识提取方法。分析结果表明 ,这种方法 ,可以实现更高的计算效率 ,并得到更好的标识效果     

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     

Generalisation of inter-layer intra prediction for scalable video coding

In the scalable video coding (SVC) standard, a simple inter-layer intra prediction (ILIP) method has been adopted to reduce the bit rate of scalable video sequences. Proposed is an improved ILIP method by generalising the original one adopted in the SVC. Experimental results show that the proposed method can reduce bit rates by 4.1 to 5.9%, compared with the original one, while average PSNR is not decreased.     

Directional residue prediction with motion alignment for video coding

A directional residue prediction method is proposed, in which motionaligned neighbouring residues are used in the directional prediction for residues in an inter-block. Corresponding motion estimation strategies are also designed. Experiments show that the bit rate saving can be up to 20% with a negligible decoding complexity increase.