DPCM coding of images presented in a pruned quadtree form

A new efficient method, based on a differential PCM technique, for encoding the leaves of a pruned quadtree is presented. Solutions to the problems of causality maintenance during tree scanning-encoding and of fast neighbour finding are described. The result is a constant wordlength code with a remarkable rate-distortion performance     

Wavelet transform coding for MCP error images using quadtree decomposition and ECVQ

This paper proposes a new wavelet transform video coder which employs motion compensation, wavelet decomposition, and entropy-constrained vector quantization (ECVQ), in sequence. Each of layered subimages obtained from wavelet decomposition is segmented into basic blocks, and then the blocks are selectively encoded by ECVQ according to the energy of the samples. We introduce an efficient method to encode the map representing which blocks are encoded, based on inter-band prediction followed by a quadtree encoding. The proposed coder uses a simple forward analyzer in order to optimize the encoding parameters and introduces a preprocessing of signals which normalizes the input vectors of ECVQ in order to reduce the image-dependency of ECVQ codebooks. Simulation results show that our video coder provides good PSNR (peak-to-peak signal-to-noise ratio) performance and efficient rate control.     

高效率的多视点视频编码预测结构*

预测结构是多视点视频编码(Multi-View Video Coding,MVC)研究的主要内容之一。MVC目前采用HHI(Heinrich-Hertz-Institute)提出的分层次B帧预测结构(HBP),比联播预测结构获得了更好的压缩效率。分析了多种预测结构,并针对平行摄像机采集的多视点视频序列,提出了一种新的预测结构AS_EIPP,该结构充分利用相邻视点间的相关性和多参考帧模式,进一步提高了压缩效率。在多视点视频软件测试平台JMVC8.3上进行验证,实验结果表明:新的预测结构在保证重建视频质量基本不变的前提下,压缩效率比HBP预测结构提高了1%～4%。     

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.     

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.     

Efficient coding of shape and transparency for video objects.

A novel scheme for coding gray-level alpha planes in object-based video is presented. Gray-level alpha planes convey the shape and the transparency information, which are required for smooth composition of video objects. The algorithm proposed is based on the segmentation of the alpha plane in three layers: binary shape layer, opaque layer, and intermediate layer. Thus, the latter two layers replace the single transparency layer of MPEG-4 Part 2. Different encoding schemes are specifically designed for each layer, utilizing cross-layer correlations to reduce the bit rate. First, the binary shape layer is processed by a novel video shape coder. In intra mode, the DSLSC binary image coder presented in [3] is used. This is extended here with an intermode utilizing temporal redundancies in shape image sequences. Then the opaque layer is compressed by a newly designed scheme which models the strong correlation with the binary shape layer by morphological erosion operations. Finally, three solutions are proposed for coding the intermediate layer. The knowledge of the two previously encoded layers is utilized in order to increase compression efficiency. Experimental results are reported demonstrating that the proposed techniques provide substantial bit rate savings coding shape and transparency when compared to the tools adopted in MPEG-4 Part 2.     

Efficient video coding based on audio-visual focus of attention

This paper proposes an efficient video coding method using audio-visual focus of attention, which is based on the observation that sound-emitting regions in an audio-visual sequence draw viewers’ attention. First, an audio-visual source localization algorithm is presented, where the sound source is identified by using the correlation between the sound signal and the visual motion information. The localization result is then used to encode different regions in the scene with different quality in such a way that regions close to the source are encoded with higher quality than those far from the source. This is implemented in the framework of H.264/AVC by assigning different quantization parameters for different regions. Through experiments with both standard and high definition sequences, it is demonstrated that the proposed method can yield considerable coding gains over the constant quantization mode of H.264/AVC without noticeable degradation of perceived quality.     

基于小波变换的预测四叉树图像编码

本文提出了一种图像编码的新算法,该算法利用了图像小波系数在频带内部与频带间的相关性,属于带内编码与带间编码的混合.在同一频带内将系数分块,随比特面的移动,将块由大到小进行四叉树分裂,以期最大限度的利用块内系数的相关性,克服了固定大小块的不足.同时在编码的过程中加入了预测过程,用上一比特平面的显著系数在当前比特面对其邻域和子节点系数进行预测,将上一比特平面的显著系数的邻域和子节点系数从块中取出单独编码,从而实现对块的裁剪,以使块的形状更符合实际的情况.最后熵编码采用的了基于上下文的算术编码,提出了四种上下文编码模型.通过对比实验表明,该方法的压缩性能较SPIHT、SQP、QT_L均有不同程度的提高.     

Efficient video coding with fractional resolution sprite prediction technique

An efficient algorithm for dynamic sprite-based video coding with fractional resolution motion compensations is presented. Different from the traditional sprite coding, the global motion and local motion are jointly compensated at two stages. The new techniques, developed in a JVT codec, are also utilised. Experimental results demonstrate that the proposed algorithm can averagely save 8% bit rate compared to JVT codec for the typical test sequences.     

Efficient early direct mode decision for multi-view video coding

Multi-view video coding (MVC) uses various prediction modes and exhaustive mode decision to achieve high coding efficiency. However, the introduced heavy computational complexity becomes the bottleneck of the practical application of MVC. For this, an efficient early Direct mode decision for MVC is proposed in this paper. Based on the observation that the Direct mode is highly possible to be the optimal mode, the proposed method first computes the rate distortion (RD) cost of the Direct mode and compares this RD cost value with an adaptive threshold for providing an early termination chance as follows. If this RD cost value is smaller than the adaptive threshold, the Direct mode will be selected as the optimal mode and the checking process of the remaining modes will be skipped; otherwise, all the modes will be checked to select the one with the minimum RD cost as the optimal mode. Note that the above-mentioned adaptive threshold is determined as the median prediction value of a set of thresholds, which are derived by using the spatial, temporal and inter-view correlations between the current macroblock (MB) and its neighboring MBs, respectively. Experimental results have demonstrated that the proposed method is able to significantly reduce the computational complexity of MVC with negligible loss of coding efficiency, compared with the exhaustive mode decision in MVC.     

Efficient reconstruction scheme for transform domain Wyner-Ziv video coding

To minimize the errors of the reconstructed values and improve the quality of decoded image,an efficient reconstruction scheme for transform domain Wyner-Ziv (WZ) video coding is proposed.The reconstruction scheme exploits temporal correlation of the coefficient bands,the WZ decoded bits stream and the side information efficiently.When side information is outside the decoded quantization bin,the reconstructed value is derived using expectation of the WZ decoded bit stream and the side information.When side information is within the decoded quantization bin,the reconstructed value is derived using the biased predictor.Simulation results show that the proposed reconstruction scheme gains up to 1.32 dB compared with the commonly used boundary reconstruction scheme at the same bit rates and similar computation cost.     

Efficient entropy coding scheme for H.264/AVC lossless video coding

Context-based adaptive variable length coding (CAVLC) and context-based adaptive binary arithmetic coding (CABAC) are entropy coding methods employed in the H.264/AVC standard. Since these entropy coders are originally designed for encoding residual data, which are zigzag scanned and quantized transform coefficients, they cannot provide adequate coding performance for lossless video coding where residual data are not quantized transform coefficients, but the differential pixel values between the original and predicted pixel values. Therefore, considering the statistical characteristics of residual data in lossless video coding, we newly design each entropy coding method based on the conventional entropy coders in H.264/AVC. From the experimental result, we have verified that the proposed method provides not only positive bit-saving of 8% but also reduced computational complexity compared to the current H.264/AVC lossless coding mode.     

Wavelet image compression - the quadtree coding approach

Perfect reconstruction, quality scalability and region-of-interest coding are basic features needed for the image compression schemes used in telemedicine applications. This paper proposes a new wavelet-based embedded compression technique that efficiently exploits the intraband dependencies and uses a quadtree-based approach to encode the significance maps. The algorithm produces a losslessly compressed embedded data stream, supports quality scalability and permits region-of-interest coding. Moreover, experimental results obtained on various images show that the proposed algorithm provides competitive lossless/lossy compression results. The proposed technique is well-suited for telemedicine applications that require fast interactive handling of large image sets over networks with limited and/or variable bandwidth     

Optimized quadtree for Karhunen-Loeve transform in multispectralimage coding

A new multispectral image compression technique based on the Karhunen-Loeve transform (KLT) and the discrete cosine transform (DCT) is proposed. The quadtree for determining the transform block size and the quantizer for encoding the transform coefficients are jointly optimized in a rate-distortion sense. The problem is solved by a Lagrange multiplier approach. After a quadtree is determined by this approach, a one-dimensional (1-D) KLT is applied to the spectral axis for each block before the DCT is applied on the spatial domain. The eigenvectors of the autocovariance matrix, the quantization scale, and the quantized transform coefficients for each block are the output of the encoder. The overhead information required in this scheme is the bits for the quadtree, KLT, and quantizer representation.     

Efficient multiple-example based super-resolution for symmetric mixed resolution stereoscopic video coding

In this paper, we first propose a new symmetric mixed resolution stereoscopic video coding (SMRSVC) model which can provide clear bitrate-reduction and visual merits. Based on the newly proposed SMRSVC model, we then propose a quality-efficient multiple-example based super-resolution method. In the proposed super-resolution method, the four block examples selected from the forward and backward key-frames, the reference super-resolved frame, and the interview super-resolved frame are referred so as to effectively fuse the high frequency component of the super-resolved current block of the downsampled non-key-frame, and then an enhanced super-resolved non-key-frame is followed. Based on six test stereoscopic video sequences, the experimental results demonstrate that besides the bitrate-saving effect, the proposed super-resolution method for the proposed SMRSVC model also has better quality performance in terms of six well-known quality metrics when compared with several state-of-the-art methods for the previous asymmetric resolution stereoscopic video coding model and the SMRSVC model.     

Efficient information hiding in H.264/AVC video coding

This paper proposes a new real-time information hiding algorithm on latest H.264/AVC video coding standard. The information is embedded into the Trailing Ones of 4×4 blocks during the Context-based Adaptive Variable Length Coding (CAVLC) process. This algorithm is efficient with low computational complexity. The simulation results show that the degradation of video quality is negligible, and the same overall bit-stream length is maintained. Based on this information hiding method, a video subtitle transmission scheme is proposed. Under the simulation of different RTP packet loss channels, the embedded information can be well recovered. The comparison with other algorithms shows the superiority of our proposed method.     

Efficient block size selection in H.264 video coding standard

Selecting an efficient variable block size mode in H.264 video coding standard for better compression performance is considered. The proposed scheme is based on a 3D recursive search algorithm and takes into account the motion vector cost and previous frame information. The best mode for the current macroblock is obtained by analysing the modes for a maximum of four macroblocks in the current and previous frames. An improvement in the encoding time with negligible impact on subjective and quantitative performance has been achieved.     

Efficient HD video coding with joint first-order-residual (FOR) and second-order-residual (SOR) coding technique

A new video coding algorithm called the first-order-residual/second-order-residual (FOR/SOR) codec is proposed for high definition (HD) video coding in this work. Several advanced coding techniques are adopted in the proposed FOR/SOR codec. For the FOR codec, the well known block-based motion compensated predictive codec is used to exploit temporal and spatial correlations in input image frames. However, it is observed that there still exists structured residual signal after the FOR coding, and a SOR coder is developed to encode residual image frames efficiently. To improve the coding performance furthermore, we consider bit allocation between the FOR and SOR coders at the same block and determine their optimal quantization parameters systematically. It is shown by experimental results that the proposed FOR/SOR codec outperforms H.264/AVC significantly in HD video coding.     

Efficient quadtree based block-shift filtering for deblocking and deringing

The existing implementations of block-shift based filtering algorithms for deblocking are hard to achieve good smoothing performance and low computation complexity simultaneously due to their fixed block size and small shifting range. In this paper, we propose to integrate quadtree (QT) decomposition with the block-shift filtering for deblocking. By incorporating the QT decomposition, we can easily find the locations of uniform regions and determine the corresponding suitable block sizes. The variable block sizes generated by the QT decomposition facilitate the later block-shift filtering with low computational cost. In addition, large block based shift filtering can provide better deblocking results because the smoothing range of large blocks spans over the conventional 8 × 8 block size. Furthermore, we extend the proposed QT based block-shifting algorithm for deringing JPEG2000 coded images. Experimental results show the superior performance of our proposed algorithms.