Multiview depth coding based on combined color/depth segmentation

In this paper, a new coding method for multiview depth video is presented. Considering the smooth structure and sharp edges of depth maps, a segmentation based approach is proposed. This allows further preserving the depth contours thus introducing fewer artifacts in the depth perception of the video. To reduce the cost associated with partition coding, an approximation of the depth partition is built using the decoded color view segmentation. This approximation is refined by sending some complementary information about the relevant differences between color and depth partitions. For coding the depth content of each region, a decomposition into orthogonal basis is used in this paper although similar decompositions may be also employed. Experimental results show that the proposed segmentation based depth coding method outperforms H.264/AVC and H.264/MVC by more than 2 dB at similar bitrates.     

Block transform image coding by multistage vector quantization withoptimal bit allocation

A multistage vector quantization with optimal bit allocation (MVQ-OBA) in the transform domain is presented. A set of bit allocation planes is first obtained by slicing a (scalar) optimal bit allocation map where the number of bits assigned to each coefficient is proportional to the coefficient variance. The set of bit allocation planes determines the coefficients to be used and the codebook size at each stage. The vector dimensionalities are restricted to small values and relatively small codebooks are used, thus reducing both the overhead required for transmitting the codebooks and the complexity in codebook design. The computer simulation results demonstrate that MVQ-OBA is competitive with many other transform coding techniques including variable length transform coding. MVQ-OBA is well suited for progressive transmission     

基于中心凹恰可觉察失真模型的多视点深度视频编码方法

针对深度视频压缩中存在的大量视觉冗余,提出了一种基于中心凹恰可觉察失真(FJND)模型的深度视频编码方法。首先通过左右通道的彩色和深度视频绘制虚拟视点图像,并利用FJND模型得到虚拟视点图像的FJND,然后根据深度视频中几何偏移和深度值失真之间的关系确定深度视频左通道的可允许失真,将深度视频左通道分区域采用自适应量化参数进行编码,并对右通道的深度视频根据与左通道量化参数的关系进行编码。实验结果表明,本文方法在相同码率下,虚拟视点图像质量平均提高0.48dB;在相同虚拟视点图像的绘制质量下,深度视频编码码率平均减少26%。     

On RD optimized progressive image coding using JPEG

Among the many different modes of operations allowed in the current JPEG standard, the sequential and progressive modes are the most widely used. While the sequential JPEG mode yields essentially the same level of compression performance for most encoder implementations, the performance of progressive JPEG depends highly upon the designed encoder structure. This is due to the flexibility the standard leaves open in designing progressive JPEG encoders. In this work, a rate-distortion (RD) optimized JPEG compliant progressive encoder is presented that produces a sequence of scans, ordered in terms of decreasing importance. Our encoder outperforms an optimized sequential JPEG encoder in terms of compression efficiency, substantially at low and high bit rates. Moreover, unlike existing JPEG compliant encoders, our encoder can achieve precise rate/distortion control. Substantially better compression performance and precise rate control, provided by our progressive JPEG compliant encoding algorithm, are two highly desired features currently sought for the emerging JPEG-2000 standard.     

Sub-band coding with adaptive bit allocation

The paper presents an efficient method for speech encoding which is based on the well known idea of sub-band coding. Typically, the frequency range from 0.3 kc/s to 3.4 kc/s is split into four sub-bands, and the sub-band signals are encoded separately with different accuracies by means of familiar PCM techniques. An adaptive bit allocation scheme is introduced here, in order to replace the usual form of a fixed distribution of the bit rate among the sub-bands. Listening tests have shown that by these means the bit rate can be reduced by more than 2.5 kb/s without degrading speech quality. Accordingly, highly intelligible reproduction of speech is possible at bit rates below 7 kb/s.     

Optimal bit allocation for FGS coding

A new bit allocation scheme for fine-granular-scalability (FGS) video coding is proposed. Differing from traditional bit allocation schemes, the focus is on understanding the relationship between rate-distortion analysis and nonzero binary-scaled coefficients (NZBC) in the bitplane coding. An optimal strategy for NZBC coding is then derived and experimental results are given for a comparison of the new scheme with uniform bit allocation.     

Optimised frequency-domain bit allocation for video coding

An optimal frequency domain bit allocation technique is presented. A Lagrange multiplier based approach is used for the rate-distortion optimisation of a quantisation matrix in video coding. Since the optimal quantisation matrix is heavily dependent on the choice of quantiser, the quantiser is also jointly optimised in order to alleviate the interaction between the two. The complexity of the algorithm is analysed, and it is shown to be directly proportional to the number of possible quantisation matrices and quantisation scales. Experimental results comparing the new technique with a conventional video encoder are also presented.     

Interlayer bit allocation for scalable video coding

In this paper, we present a theoretical analysis of the distortion in multilayer coding structures. Specifically, we analyze the prediction structure used to achieve temporal, spatial, and quality scalability of scalable video coding (SVC) and show that the average peak signal-to-noise ratio (PSNR) of SVC is a weighted combination of the bit rates assigned to all the streams. Our analysis utilizes the end user's preference for certain resolutions. We also propose a rate-distortion (R-D) optimization algorithm and compare its performance with that of a state-of-the-art scalable bit allocation algorithm. The reported experiment results demonstrate that the R-D algorithm significantly outperforms the compared approach in terms of the average PSNR.     

ViSTRA2: Video coding using spatial resolution and effective bit depth adaptation

We present a new video compression framework (ViSTRA2) which exploits adaptation of spatial resolution and effective bit depth, down-sampling these parameters at the encoder based on perceptual criteria, and up-sampling at the decoder using a deep convolution neural network. ViSTRA2 has been integrated with the reference software of both the HEVC (HM 16.20) and VVC (VTM 4.0.1), and evaluated under the Joint Video Exploration Team Common Test Conditions using the Random Access configuration. Our results show consistent and significant compression gains against HM and VVC based on Bjønegaard Delta measurements, with average BD-rate savings of 12.6% (PSNR) and 19.5% (VMAF) over HM and 5.5% (PSNR) and 8.6% (VMAF) over VTM.     

Comparison between adaptive search and bit allocation algorithmsfor image compression using vector quantization

This article discusses bit allocation and adaptive search algorithms for mean-residual vector quantization (MRVQ) and multistage vector quantization (MSVQ). The adaptive search algorithm uses a buffer and a distortion threshold function to control the bit rate that is assigned to each input vector. It achieves a constant rate for the entire image but variable bit rate for each vector in the image. For a given codebook and several bit rates, we compare the performance between the optimal bit allocation and adaptive search algorithms. The results show that the performance of the adaptive search algorithm is only 0.20-0.53 dB worse than that of the optimal bit allocation algorithm, but the complexity of the adaptive search algorithm is much less than that of the optimal bit allocation algorithm.     

Analysis of low bit rate image transform coding

Calculations based on high-resolution quantizations prove that the distortion rate D(R¯) of an image transform coding is proportional to 2^-2R when R¯ is large enough. In wavelet and block cosine bases, we show that if R¯<1 bit/pixel, then D(R¯) varies like R¯^1-2γ, where γ remains of the order of 1 for most natural images. The improved performance of embedded codings in wavelet bases is analyzed. At low bit rates, we show that the compression performance of an orthonormal basis depends mostly on its ability to approximate images with a few nonzero vectors     

Optimal bit allocation for coding of video signals over ATMnetworks

We consider optimal encoding of video sequences for ATM networks. Two cases are investigated. In one, the video units are coded independently (e.g., motion JPEG), while in the other, the coding quality of a later picture may depend on that of an earlier picture (e.g., H.26x and MPEGx). The aggregate distortion-rate relationship for the latter case exhibits a tree structure, and its solution commands a higher degree of complexity than the former. For independent coding, we develop an algorithm which employs multiple Lagrange multipliers to find the constrained bit allocation. This algorithm is optimal up to a convex-hull approximation of the distortion-rate relations in the case of CBR (constant bit-rate) transmission. It is suboptimal in the case of VBR (variable bit-rate) transmission by the use of a suboptimal transmission rate control mechanism for simplicity. For dependent coding, the Lagrange-multiplier approach becomes rather unwieldy, and a constrained tree search method is used. The solution is optimal for both CBR and VBR transmission if the full constrained tree is searched. Simulation results are presented which confirm the superiority in coding quality of the encoding algorithms. We also compare the coded video quality and other characteristics of VBR and CBR transmission     

Subband coding of image sequences at low bit rates

In this paper a low bit rate subband coding scheme for image sequences is described. Typically, the scheme is based on temporal DPCM in combination with an intraframe subband coder. In contrast to previous work, however, the subbands are divided into blocks onto which conditional replenishment is applied, while a bit allocation algorithm divides the bits among the blocks assigned for replenishment. A solution is given for the ‘dirty window’ effect by setting blocks to zero that were assigned to be replenished but received no bits. The effect of motion compensation and the extension to color images are discussed as well. Finally, several image sequence coding results are given for a bit rate of 300 kbit/s.     

A new algorithm for BTC image bit plane coding

A new look-up table technique for the coding of the block truncated image bit plane is presented which yields better images in the subjective as well as in the mean square sense compared to the one proposed by Mitchell and Delp (1980)     

On color transforms and bit allocation for optimal subband image compression

Although subband transform coding is a useful approach to image compression and communication, the performance of this method has not been analyzed so far for color images, especially when the selection of color components is considered. Obviously, the RGB components are not suitable for such a compression method due to their high inter-color correlation. On the other hand, the common selection of YUV or YIQ is rather arbitrary and in most cases not optimal. In this work we introduce a rate–distortion model for color image compression and employ it to find the optimal color components and optimal bit allocation (optimal rates) for the compression. We show that the DCT (discrete cosine transform) can be used to transform the RGB components into an efficient set of color components suitable for subband coding. The optimal rates can be also used to design adaptive quantization tables in the coding stage with results superior to fixed quantization tables. Based on the presented results, our conclusion is that the new approach can improve presently available methods for color image compression and communication.     

High compression image coding using an adaptive morphologicalsubband decomposition

A morphological subband decomposition with perfect reconstruction is proposed. Critical subsampling is achieved. The reconstructed images using this decomposition do not suffer from any ringing effect. In order to avoid poor texture representation by the morphological filters an adaptive subband decomposition is introduced. It chooses linear filters on textured regions and morphological filters otherwise. A simple and efficient texture detection criterion is proposed and applied to the adaptive decomposition. Comparisons to other coding techniques such as JPEG and linear subband coding show that the proposed scheme performs significantly better both in terms of PSNR and visual quality     

面向编码和绘制的多视点图像深度估计

针对自由视点三维电视系统中深度估计不准确将给后续多视点深度编码和虚拟视点绘制带来困难的问题,提出一种面向编码和绘制的多视点图像深度估计算法。首先对初始深度进行一致性检查,并采用自适应匹配误差策略删除不可靠的匹配以减小初始深度的误匹配。然后根据融合准则将多幅参考深度图合成为一幅深度图以提高深度图的精度。最后,采用多边滤波...     

基于3D-HEVC的多视点纹理加深度的联合比特分配算法

首先依据视频序列的统计特性,建立纹理 比特率和深度 图比特率与虚拟视点失真之间模型;然后分别建立拉格朗日算子与纹理、深度图比特率的对 应关系,在前 两步的基础上构建由虚拟视点失真模型和拉格朗日算子的代价方程,为了保证目标 码率与输出码 率在一定的误差范围内,建立纹理比特率和深度比特率的受限约束方程;最后利用目标码率 的约束方程,求解 出最优的纹理比特率和深度图比特率。实验结果表明,提出的算法与目前流行的多视点纹理 加深度的算法 相比,在相同的编码比特率情况下,虚拟视点和基本视点客观质量平均提高0.15dB,因此具有更高的编码效率。     

一种基于立体视觉显著性的多视点视频比特分配方法

针对多视点立体视频压缩编码,提出了一种基于立 体视觉显著性的比 特分配方法。研究综合利用多视点立体视频数据中场景的运动、深度以及深度边缘信息提取 人眼感兴趣区 域(ROI)的方法;然后根据ROI的划分结果优化区域比特分配。实验结果表 明,本文提出的算法能有效提 高ROI区域的编码性能,同时整体视频的率失真性能有一定程度的提高。