Intra-Predictive Transforms for Block-Based Image Coding

This paper presents the theory and the design of intra-predictive transforms, which unify the inter-block prediction and block-based transforms in block-based image coding. Motivated by interpreting inter-block prediction as a transform with a larger size, we derive the concept of intra-predictive transforms. Conventional predictions and transforms can be viewed as special cases of intra-predictive transforms. Intra-predictive transforms are able to exploit both inter and intra-block correlations. We derive the tight upper bound of the coding gain of intra-predictive transforms for stationary Gaussian sources. It turns out that the coding gain can be greater than that of conventional transforms. The optimal intra-predictive transform that achieves the upper bound is also derived. We also design a practical intra-predictive transform using frequency-domain prediction that can achieve better performance in image coding while exhibiting low computational complexity. Experimental results confirm the effectiveness of the proposed intra-predictive transforms in block-based image coding systems and show the improvements over the current design.     

Intraframe Image Coding by Cascaded Hadamard Transforms

Various image coding schemes have been studied for digital transmission of videophone signals. The Hadamard transform, which is now studied for the transmission of pictures such as those from satellites, has been considered too complicated for public use, though the characteristics such as the ratio of bit-rate reduction are more desirable than those of differential pulse-code modulation (DPCM). We have found a very simple scheme of the transform, where digitized videophone signals are transformed to Hadamard components all digitally just byndigital adders and some shift registers for 2ⁿth-order transform. For example, three adders are necessary for eighth-order transform. It is extendable to two-dimensional transform with ease. We have made an experimental model running in real time. Experiments and theoretical calculation have shown that 3 bits/sample are required for good picture quality in the case of two-dimensional(4 times 2)th transform and 0.5 bits more for one-dimensional eighthorder transform.     

级联叠式变换的低内存实现

本文提出了级联叠式变换(Hierarchical Lapped Transform,HLT)的一种低内存的实现算法.该算法的正、逆变换均具有低内存需求且该内存需求仅与所采用的HLT相关,而与待处理的信号长度无关.该算法产生的子带系数与HLT的全局变换方法产生的子带系数完全相同.实验表明,本文提出的HLT实现算法具有内存消耗低、扩展性良好的优点.     

The Most General Time-Varying Filter Bank and Time-Varying Lapped Transforms

In this paper, a model-based method is used to analyze the most general time-varying filter bank, where all parameters in the filter bank change with time, including filter length, decimator factor, and the number of channel. Through modeling the time-varying filter bank at a fixed time point as a time-invariant filter bank, we change the study of the most general time-varying filter bank to study of the established model. Based on the model, the most general time-varying filter bank is analyzed in both polyphase domain and modulation domain. The general perfect reconstruction (PR) conditions of the most general time-varying filter bank are given using time-varying polyphase matrices in the polyphase domain. In the modulation domain, the time-varying distortion-matrix is presented, and the distortion-free condition of the most general time-varying filter bank is given. Based on the established theory for the most general time-varying filter bank, in the second part of this paper, the time-varying cosine-modulated lapped transform (TV-MLT) as an example is analyzed in detail. An interesting design approach called the window-switching technique, used to design the time-varying prototype windows for a perfectly reconstructed TV-MLT, is introduced. The window-switching technique provides us with the possibility to design a perfectly reconstructed TV-MLT without complex mathematical optimization computation, and simply by graphically building the prototype windows in the transition period based on the given diagrams of the prototype windows before and after the transform changing.     

匹配视觉生理机制的方向分解图象编码

本文对方向分解图像编码进行了系统研究。与Kunt方案相比,提出了更有效的边缘信息选择和编码算法,改进了内插方法和模型,并采用了新的方向滤波器设计方法,基于上述改进,建立了一套完整的匹配视觉生理机制的方向分解图像编码算法。系统模拟实验表明,当数据压缩比近60:1时,采用本方案仍能获得较好的图像质量。     

基于静止图像的小波图像编码

小波图像编码是近十几年发展起来的一种新兴的图像编码方法，目前对其研究较为广泛。主要介绍了当前基于静止图像的小波编码的原理、基本特性、现有方法和发展前景，以及所存在的问题。希望以此进一步推动这一前沿领域的研究工作。     

Fourier Transforms and Directional Couplers (Correspondence)

The excellent review of Bolinder on the applications of Fourier transforms in wave theory, particularly the section on "Coupling of Waves," suggested that the readers of these Transactions might also be interested in some related work performed by this writer some time ago. A report on this work contains a section on the use of Fourier integral and series methods for directional coupler design. In connection with directional couplers, this letter also can be considered as noting a further addition to the useful bibliography of Schwartz. Although not widely distributed, the aforementioned report has been available since late 1947 in the Document Room of the Research Laboratory of Electronics at the Massachusetts Institute of Technology as No. SPE-239. It should be emphasized that this letter is not intended to start a controversy as to who did what first, but rather to bring to the readers' attention a report of possible interest.     

广义高斯信源的自适应编码研究

首先介绍了当前最新的几种视频编码标准并且进行了比较,熵编码是每一个视频编码标准必须认真研究的课题,为了减少由于失配所带来的效率损失,本文提出了一种自适应编码技术:自适应指数哥伦布码,并与自适应算术编码进行了比较.分析和仿真都表明即使信源特性在大范围内发生变化,自适应指数哥伦布码对于保持高的编码效率是足够稳健的(90%以上的情况),同时保持了指数哥伦布码和哥伦布-莱期码的简洁性.     

Gray-Scale Image Coding for Freeze-Frame Videoconferencing

A new gray-scale image coding technique has been developed, in which an extended DPCM approach has been combined with entropy coding. This technique has been implemented in a freeze-frame videoconferencing system which is now operational at IBM sites throughout the world. Following image preprocessing, the two fields of the interlaced 512 x 480 pixel video frame are compressed sequentially with different algorithms. The reconstructed image quality is improved by subsequent image postprocessing, the final reconstructed image being almost indistinguishable from the original image. Typical gray-scale video images compress to about a half bit per pixel and transmit over 4.8 kbit/s dial-up telephone lines in about a half minute. The gray-scale image processing and compression algorithms are described in this paper.     

分形图像压缩方法

分形几何方法是一种新的图像压缩编码方法。本文介绍了分形几何和分形图像压缩的一些基本概念，以及以分形为基础的几种图像压缩编码方法。     

Spherical Coding Algorithm for Wavelet Image Compression

In recent literature, there exist many high-performance wavelet coders that use different spatially adaptive coding techniques in order to exploit the spatial energy compaction property of the wavelet transform. Two crucial issues in adaptive methods are the level of flexibility and the coding efficiency achieved while modeling different image regions and allocating bitrate within the wavelet subbands. In this paper, we introduce the ldquospherical coder,rdquo which provides a new adaptive framework for handling these issues in a simple and effective manner. The coder uses local energy as a direct measure to differentiate between parts of the wavelet subband and to decide how to allocate the available bitrate. As local energy becomes available at finer resolutions, i.e., in smaller size windows, the coder automatically updates its decisions about how to spend the bitrate. We use a hierarchical set of variables to specify and code the local energy up to the highest resolution, i.e., the energy of individual wavelet coefficients. The overall scheme is nonredundant, meaning that the subband information is conveyed using this equivalent set of variables without the need for any side parameters. Despite its simplicity, the algorithm produces PSNR results that are competitive with the state-of-art coders in literature.     

Least-Squares-Based Switching Structure for Lossless Image Coding

Many coding methods are more efficient with some images than others. In particular, run-length coding is very useful for coding areas of little changes. Adaptive predictive coding achieves high coding efficiency for fast changing areas like edges. In this paper, we propose a switching coding scheme that will combine the advantages of both run-length and adaptive linear predictive coding. For pixels in slowly varying areas, run-length coding is used; otherwise least-squares (LS)-adaptive predictive coding is used. Instead of performing LS adaptation in a pixel-by-pixel manner, we adapt the predictor coefficients only when an edge is detected so that the computational complexity can be significantly reduced. For this, we use a simple yet effective edge detector using only causal pixels. This way, the proposed system can look ahead to determine if the coding pixel is around an edge and initiate the LS adaptation in advance to prevent the occurrence of a large prediction error. With the proposed switching structure, very good prediction results can be obtained in both slowly varying areas and pixels around boundaries. Furthermore, only causal pixels are used for estimating the coding pixels in the proposed encoder; no additional side information needs to be transmitted. Extensive experiments as well as comparisons to existing state-of-the-art predictors and coders will be given to demonstrate its usefulness.     

Quadtree Optimization for Image and Video Coding

The optimal design of quadtree-based codecs is addressed. Until now, work in this area has focused on the optimization of the quadtree structure for a given set of leaf quantizers while neglecting the design of the quantizers themselves. In cases where the leaf quantizers have been considered, codebooks have been optimized without regard to the ultimate quadtree segmentation. However, it is not sufficient to consider each problem independently, as separate optimization leads to an overall suboptimal solution. Rather, joint design of the quadtree structure and the leaf codebooks must be considered for overall optimality. The method we suggest is a quadtree constrained version of the entropy-constrained vector quantization design method. To this end, a centroid condition for the leaf codebooks is derived that represents a necessary optimality condition for variable-rate quadtree coding. This condition, when iterated with the optimal quadtree segmentation strategy of Sullivan and Baker results in a monotonically descending rate-distortion cost function, and consequently, an (at least locally) optimal quadtree solution.     

图象信号的三态ADM编码的研究

本文首次提出了三态自适应增量调制编码方法。通过对图象信号进行编码和滤波的模拟研究,证明了这种三态ADM编码的动态范围比二态ADM编码增大6—10dB,信噪比改善约为1.5—3.5dB,并保持了可实现无乘法滤波的特点。     

Document Image Coding for Processing and Retrieval

Document images belong to a unique class of images where the information is embedded in the language represented by a series of symbols on the page rather than in the visual objects themselves. Since these symbols tend to appear repeatedly, a domain-specific image coding strategy can be designed to facilitate enhanced compression and retrieval. In this paper we describe a coding methodology that not only exploits component-level redundancy to reduce code length but also supports efficient data access. The approach identifies and organizes symbol patterns which appear repeatedly. Similar components are represented by a single prototype stored in a library and the location of each component instance is coded along with the residual between it and its prototype. A representation is built which provides a natural information index allowing access to individual components. Compression results are competitive and compressed-domain access is superior to competing methods. Applications to network-related problems have been considered, and show promising results.     

Vector Lifting Schemes for Stereo Image Coding

Many research efforts have been devoted to the improvement of stereo image coding techniques for storage or transmission. In this paper, we are mainly interested in lossy-to-lossless coding schemes for stereo images allowing progressive reconstruction. The most commonly used approaches for stereo compression are based on disparity compensation techniques. The basic principle involved in this technique first consists of estimating the disparity map. Then, one image is considered as a reference and the other is predicted in order to generate a residual image. In this paper, we propose a novel approach, based on vector lifting schemes (VLS), which offers the advantage of generating two compact multiresolution representations of the left and the right views. We present two versions of this new scheme. A theoretical analysis of the performance of the considered VLS is also conducted. Experimental results indicate a significant improvement using the proposed structures compared with conventional methods.     

Channel Error Recovery for Transform Image Coding

A method is presented to automatically inspect the block boundaries of a reconstructed two-dimensional transform coded image, to locate blocks which are most likely to contain errors, to approximate the size and type of error in the block, and to eliminate this estimated error from the picture. This method uses redundancy in the source data to provide channel error correction. No additional channel error protection bits or changes to the transmitter are required. It can be used when channel errors are unexpected prior to reception.     

An Adaptive Strategy for Hybrid Image Coding

In hybrid coding technique, the sampled data are divided into blocks ofN times Msamples. Next, each block is transformed to generate a one-dimensional transform of each line in the block. The transform coefficients are then processed by a block of DPCM encoders which uncorrelate the data in the second dimension and qnantize the uncorrelated samples using appropriate quantizers. In this study an adaptive hybrid coding technique is proposed based on using a single quantizer (A/D converter) to quantize the transform coefficients and using a variable-rate algorithm for coding the quantized coefficients. The accuracy of the A/D converter (number of bits per sample) determines the fidelity of the system. The buffercontrol algorithm controls the accuracy of the A/D converter for each block resulting in a fixed-rate encoder system. Experimental results have shown a stable buffer condition and reconstructed images with a higher fidelity than nonadaptive hybrid systems.     

图像压缩编码技术

章论述了经典图像编码方法和现代图像编码方法的基本原理，指出将多种编码算法融合在一个编码器中是新一代图像编码的研究方向。     

Slant Transform Image Coding

A new unitary transform called the slant transform, specifically designed for image coding, has been developed. The transformation possesses a discrete sawtoothlike basis vector which efficiently represents linear brightness variations along an image line. A fast computational algorithm has been found for the transformation. The slant transformation has been utilized in several transform image-coding systems for monochrome and color images. Computer simulation results indicate that good quality coding can be accomplished with about 1 to 2 bits/pixel for monochrome images and 2 to 3 bits/pixel for color images.