小波图像的膨胀-游程编码算法

提出了一种基于形态膨胀运算和游程编码的新型小波编码器膨胀-游程(Dilation-Run)算法。编码器根据图像小波变换后重要系数的带内聚类特性和重要系数分布的带间相似性,利用数学形态学中的膨胀运算搜索并编码各聚类中的重要系数;同时使用一种高效的游程编码技术对各聚类的种子系数,即膨胀运算起始点的位置进行编码,从而避免了小波图像中非重要系数的逐个编码。编码器算法简单,并且基于位平面实现,因此输出码流具有渐进性。实验结果表明,膨胀-游程算法的性能优于零树小波编码器SPIHT,并能与两种形态学小波编码器MRWD 和SLCCA的性能媲美。对于聚类特性显著的图像,算法的性能则优于上述形态学小波编码器。     

Arithmetic coding for image compression with adaptive weight-context classification

In this paper, a new binary arithmetic coding strategy with adaptive-weight context classification is introduced to solve the context dilution and context quantization problems for bitplane coding. In our method, the weight, obtained using a regressive–prediction algorithm, represents the degree of importance of the current coefficient/block in the wavelet transform domain. Regarding the weights as contexts, the coder reduces the context number by classifying the weights using the Lloyd–Max algorithm, such that high-order is approximated as low-order context arithmetic coding. The experimental results show that our method effectively improves the arithmetic coding performance and outperforms the compression performances of SPECK, SPIHT and JPEG2000.     

Dilation-run wavelet image coding

The run-length coding and the morphological representation are two classical schemes for wavelet image coding. The run-length coders have the advantage of simplicity by recording the lengths of zero-runs between significant wavelet coefficients but at the expense of yielding an inferior rate-distortion performance. The morphology-based coders, on the other hand, utilize the morphological dilation operation to delineate the clusters of significant coefficients for improving coding performance. In this paper, a novel dilation-run image coding algorithm is developed by taking the advantages of both schemes, in which the clustered significant coefficients are extracted by using the morphological dilation operation and the insignificant coefficients between the extracted clusters are coded by using the run-length coding method. The proposed dilation-run image coder is implemented in the framework of bitplane coding for producing embedded bitstreams. Compared with several state-of-the-art wavelet image coding methods, the proposed dilation-run image coding method achieves comparable rate-distortion coding performance, especially more attractive for fingerprint type of imageries.     

An enhanced entropy coding scheme for HEVC

This paper presents a modification to Context-based Adaptive Binary Arithmetic Coding (CABAC) in High Efficiency Video Coding (HEVC), which includes an improved context modeling for transform coefficient levels and a binary arithmetic coding (BAC) engine with low memory requirement. In the improved context modeling for transform coefficient levels, the context model index for significance map is dependent on the number of the significant neighbors covered by a local template and its position within transform block (TB). To limit the total number of context models for significance map, TBs are split into different regions based on the coefficient position. The same region in different TBs shares the same context model set. For the first and second bins of the truncated unary scheme of absolute level minus one, their context model indices depend on the neighbors covered by a local template of the current transform coefficient level. Specifically, the context model index for the first bin is determined by the number of neighbors covered by the local template with absolute magnitude equal to 1 and larger than 1; for the second bin, its context model index is determined by the number of neighbors covered by the local template with absolute magnitude larger than 1 and larger than 2. Moreover, TB is also split into different regions to incorporate the coefficient position in the context modeling of the first bin in luma component. In the BAC engine with low memory requirement, the probability is estimated based on a multi-parameter probability update mechanism, in which the probability is updated with two different adaption speeds and use the average as the estimated probability for the next symbol. Moreover, a multiplication with low bit capacities is used in the coding interval subdivision to substitute the large look-up table to reduce its memory consumption. According to the experiments conducted on HM14.0 under HEVC main profile, the improved context modeling for transform coefficient levels achieves 0.8%, 0.6% and 0.4% bitrate reduction on average for all intra (AI), random access (RA) and low delay (LD) configurations, respectively; the BAC engine with low memory requirement achieves 0.7%, 0.6% and 0.5% bitrate reduction on average for AI, RA and LD configurations, respectively; the overall bitrate reduction achieved by the proposed two techniques is 1.4%, 1.1% and 0.9% on average for AI, RA and LD configurations, respectively.     

基于上下文建模的分类排序小波图像编码算法

该文提出了基于上下文建模的分类排序小波图像编码算法。该方法使用与JPEG2000标准相同的上下文模型,以最小化相对熵为准则用动态规划获得优化的上下文分类。在重要性编码中结合优化的上下文分类进行排序编码。实验数据表明该算法的压缩能力优于JPEG2000,尤其适于低码率压缩。     

易于硬件实现的内嵌图像编码算法

EZBC算法综合利用了子带内和子带间系数的相关性．把零树／零块结构和基于上下文编码的优点有机结合在一起,获得了比SPHIT算法更好的压缩性能,比EBCOT更高的压缩效率。但是EZBC算法编码中的两个排序链表需要很大且非固定的存储空间,这使得EZBC算法的硬件实现非常困难。在EZBC算法的基础上提出了一种易于硬件实现、低存储量、高压缩性能的内嵌零块图像编码算法。该算法利用比特平面节点重要性状态表和上下文查找表来完成整个编码过程和形成上下文。实验结果表明,所提出的算法具有与EZBC算法基本相同的高压缩性能,但所需存储空间约为EZBC算法的四分之一,所以该算法更易于硬件实现。     

Video and image applications on narrowband and broadband isdn

Two major ISDN applications which will undoubtedly affect world-wide telecommunications in the coming decade are discussed. They are: (1) video transmission and (2) image transmission. Brief reviews of videophone chronicle and the current video coding technologies are presented. The application of videophones using p × 64 (CCITT coding algorithm up to 1·5 Mb/s) and the DCT (discrete cosine transform) algorithm for narrowband ISDN are discussed. Broadcast TV quality DS3-45 MB/s video codecs are also briefly discussed as a probable videophone system in the broadband ISDN era. The explosive growth of facsimile services is reviewed, and the progress of image coding technologies and their standards are covered. The prospects of high resolution image transfer systems with ISDN are addressed.     

一种高效的运动补偿三维小波视频编码方案

该文提出了一种高效的运动补偿三维小波视频编码方案。该方案采用运动补偿时域分析技术,以有效去除视频序列中存在的时间冗余。然后,基于视频序列的运动特征,自适应确定帧组结构,在提高编码效率的同时降低内存需求和运算复杂度。最后,根据小波图像系数特性,采用基于四叉树分裂的小波图像编码方法对三维时/空子带进行编码,以获得更高的压缩效率。实验结果表明,与其它运动补偿三维小波视频编码方法相比,该文提出的编码方案能够获得更好的性能。     

Adaptive prediction for lossless image compression

Lossless image compression is often performed through decorrelation, context modelling and entropy coding of the prediction error. This paper aims to identify the potential improvements to compression performance through improved decorrelation. Two adaptive prediction schemes are presented that aim to provide the highest possible decorrelation of the prediction error data. Consequently, complexity is overlooked and a high degree of adaptivity is sought. The adaptation of the respective predictor coefficients is based on training of the predictors in a local causal area adjacent to the pixel to be predicted. The causal nature of the training means no transmission overhead is required and also enables lossless coding of the images.The first scheme is an adaptive neural network, trained on the actual data being coded enabling continuous updates of the network weights. This results in a highly adaptive predictor, with localised optimisation based on stochastic gradient learning. Training for the second scheme is based on the recursive LMS (RLMS) algorithm incorporating feedback of the prediction error. In addition to the adaptive prediction, the results presented here also incorporate an arithmetic coding scheme, producing results which are better than CALIC.