Target Bit Rate Research Articles

Visual data compression for multimedia applications

The compression of visual information in the framework of multimedia applications is discussed. To this end, major approaches to compress still as well as moving pictures are reviewed. The most important objective in any compression algorithm is that of compression efficiency. High-compression coding of still pictures can be split into three categories: waveform, second-generation, and fractal coding techniques. Each coding approach introduces a different artifact at the target bit rates. The primary objective of most ongoing research in this field is to mask these artifacts as much as possible to the human visual system. Video-compression techniques have to deal with data enriched by one more component, namely, the temporal coordinate. Either compression techniques developed for still images can be generalized for three-dimensional signals (space and time) or a hybrid approach can be defined based on motion compensation. The video compression techniques can then be classified into the following four classes: waveform, object-based, model-based, and fractal coding techniques. This paper provides the reader with a tutorial on major visual data-compression techniques and a list of references for further information as the details of each method.

Picture Quality Editing for Variable Rate Compressed Video

This paper discusses a novel video encoding system in which a user controls the quality of the encoded video. It uses an algorithm for reallocation of target bits to the segment selected for editing or quality change. The algorithm is based on the availability of a log file containing statistics pertaining to the original run that produced the compressed video. A key aspect of the bit allocation is that subjective input from the user is used to alter the picture quality of the edit segment. Bitstream splicing is carried out to complete the process of editing. The video is initially encoded according to an automatic process without user intervention. An operator then reviews it manually and indicates the quality of specific time periods or regions to be altered. A numeric value for picture quality is assigned in the range [-5, 5]. First, a common bit pool is created by removing a percentage of bits from the time periods or regions for which quality priorities have been specified. These are then redistributed as a function of the user-selected priority. The bit assignments are adjusted resulting in the avoidance of buffer underflow. Also, the buffer occupancy at the trailing edge of the edit segment is maintained at its original level. After the assignment of new target bits, the average quantizer scale value is determined using a previously determined rate quantizer function. The video is then re-encoded with the new set of target bits to achieve the desired quality change. Bitstream and log files are updated by proper splicing.

Motion and disparity field estimation using rate-distortion optimization

A rate-distortion framework is used to define a displacement vector field estimation technique for use in video coding. This technique achieves maximum reconstructed image quality under the constraint of a target bit rate for the coding of the vector sequence. The technique may be adapted so as to limit its smoothing effect to homogeneous areas and avoid highly textured areas and edges. Use of this technique is evaluated for two application areas in which the need for high compression of displacement vector fields is particularly acute. The first is motion field coding for very-low-bit-rate image sequence transmission, as in video-phone applications. The second application area is coding for the transmission of dense disparity fields. This is needed for the generation at the receiver of intermediate viewpoints through spatial interpolation. It is also needed in a number of other applications requiring accurate depth knowledge, including three-dimensional medical data transmission and transmission of scenes to be postprocessed using depth-keyed segmentation. Experimental results illustrating the performance of the proposed technique in these application areas are presented and evaluated.

Hierarchical disparity estimation using spatial correlation

In this paper, we propose a fast hierarchical algorithm for disparity estimation, which is based on the multiresolution block matching technique with prospective disparity vectors. The disparity vectors of each template block's spatially adjacent blocks are adopted as the initial references for the template block to speed up the estimation process. The experimental results show that the proposed hierarchical estimation algorithm can reduce computation cost drastically while maintaining comparable PSNR quality. The proposed scheme also results in smoother disparity vector field compared to the exhaustive search scheme. A rate-distortion optimized hierarchical disparity estimation algorithm is also proposed to minimize the distortion of the reconstructed image sequence under a target bit rate constraint. The experimental results show that its PSNR quality is better than the full search algorithm while taking more computing power for the optimization process.

Optimization of wireframe model adaptation and motion estimation in a rate-distortion framework

A rate-distortion framework is used to define a very low-bit-rate coding scheme based on wireframe model adaptation and optimized selection of motion estimators. This technique achieves maximum reconstructed image quality under the constraint of a target bit rate for the coding of the vector field and the wireframe representation information. First, a complete scheme is proposed for hybrid two-dimensional (2D) and 3D motion estimation and compensation. The wireframe adaptation and updating is optimized for hybrid motion estimation in the rate distortion sense. A more sophisticated technique, adapted to the requirements of a very low-bit-rate coder is also proposed which considers also the transmission of the prediction error corresponding to the particular choice of the motion estimator for each object in the scene. Experimental results illustrating the performance of the proposed techniques in very low-bit-rate image sequence coding application areas are presented and evaluated. © 1998 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 9, 238–247, 1998

Optimization of wireframe model adaptation and motion estimation in a rate‐distortion framework

A rate-distortion framework is used to define a very low bit rate coding scheme based on wireframe model adaptation and optimized selection of motion estimators. This technique achieves maximum reconstructed image quality under the constraint of a target bitrate for the coding of the motion vector field, the wireframe representation information and the prediction error. Experimental results illustrating the performance of the proposed techniques in very low bit rate image sequence coding application areas are presented and evaluated.

A Hybrid Object-Oriented Very Low Bit Rate Video Codec

There are a large number of applications requiring the compression of video at Very Low Bit Rates (VLBR). Such applications include wireless video conferencing, video over the internet, multimedia database retrieval and remote sensing and monitoring. Recently, the MPEG-4 standardization effort has been a motivating factor to find a solution to this challenging problem. The existing approaches to this problem can generally be grouped into block-based, model-based, and object-oriented. Block-based approaches follow the traditional strategy of decoupling the image sequence into blocks, model-based approaches rely on complex 3-D models for specific objects that are encoded, and object-oriented approaches rely on analyzing the scene into differently moving objects. All three approaches exhibit potential problems. Block-based approaches tend to generate artifacts at the boundaries of the blocks, as well as to limit the minimum achievable bit-rate due to the fixed analysis structure of the scene. Model-based codecs are limited by the complex 3-D models of the objects to be encoded. On the other hand, object-oriented codecs can generate a significant overhead due to the analysis of the scene which needs to be transmitted, which in turn can be the limiting factor in achieving the target bit-rates. In this paper, we propose a hybrid object-oriented codec in which the correlations among the three information fields, e.g., motion, segmentation and intensity fields, are exploited both spatially and temporally. In the proposed method, additional intelligence is given to the decoder, resulting in a reduction of the required bandwidth. The residual information is analyzed into three different categories, i.e., occlusion, model failures, and global refinement. The residual information is encoded and transmitted across the channel with other side information. Experimental results are presented which demonstrate the effectiveness of the proposed approach.

A new rate control scheme using quadratic rate distortion model

A new rate control scheme is used to calculate the target bit rate for each frame based on a quadratic formulation of the rate distortion function. The distortion measure is assumed to be the average quantization scale of a frame. The rate distortion function is modeled as a second-order function of the inverse of the distortion measure. We present a closed form solution for the target bit allocation which includes the MPEG-2 TM5 rate control scheme as a special case. The model parameters are estimated using statistical linear regression analysis. Since the estimation uses the past encoded frames of the same picture prediction type (I, P, B pictures), the proposed approach is a single pass rate control technique. Because of the improved accuracy of the rate distortion function, the fluctuations of the bit counts are significantly reduced by 20-65% in the standard deviation of the bit count while the picture quality remains the same. Thus, the buffer requirement is reduced at a small increase in complexity. This technique has been adopted by the MPEG committee as part of VM5.0 in November 1996.

Optimization of quadtree segmentation and hybrid two-dimensional and three-dimensional motion estimation in a rate-distortion framework

A rate-distortion framework is used to define a very low bit-rate coding scheme based on quadtree segmentation and optimized selection of motion estimators. This technique achieves maximum reconstructed image quality under the constraint of a target bit rate for the coding of the vector field and segmentation information. First, a complete scheme is proposed for hybrid two-dimensional (2-D) and three-dimensional (3-D) motion estimation and compensation. The quadtree object segmentation is optimized for hybrid motion estimation in the rate-distortion sense. This scheme adapts to the depth of the quadtree and the technique used for motion estimation for each leaf of the tree. A more sophisticated technique, adapted to the requirements of a very low bit-rate coder, is also proposed which also considers the transmission of the prediction error corresponding to the particular choice of the motion estimator. Based on these coding schemes, two versions of a very low bit-rate image sequence coder are developed. Experimental results illustrating the performance of the proposed techniques in very low bit-rate image sequence coding application areas are presented and evaluated.

A New Bit Rate Control of MPEG with Predictive and AdaptivePerceptual Quantization

Bit rate control has been proved to be an important technique used to transmit the variable rate bit stream over a fixed rate channel in MPEG coding. In this paper, a hybrid algorithm is proposed to achieve the rate control and obtain a good picture quality. In the picture layer, the algorithm estimates numbers of bits required for different type of frames. In the macroblock layer, it utilizes the predictive and adaptive perceptual techniques in the regulation of the quantization scale to allocate the target bits. In the upper and left boundary of the picture, the macroblocks are quantized with the perceptual basis to adjust the quantization scale and in the other part of the picture a predictive method is used to update the quantization scale. By using the proposed scheme, the distortion of coding is uniformly distributed in the picture layer as well as in the macroblock layer and better bit rate control is achieved.

Improved performance H.263 under erroneous transmission conditions

The authors present an algorithm for limiting the propagation of errors in an H.263 video bit stream subject to channel degradation. The frequency of occurence of INTRA coded frames (I-frame) is increased to thwart the temporal dependency of predicted frames (P-frame). The proposed algorithm ensures that all 8-bit length INTRADC coefficients of I-frames are received by inducing a change in their order of transmission. To combat the effect of channel corruption on INTRADC coefficients, a half rate convolutional coder is used. The synchronisation is protected by sending synch words at fixed-length intervals within the bit stream. Results showed that the proposed algorithm improved the quality of service (QoS) of the video coder on both the subjective and objective scales, even when similar target bit-rates are considered.

HD-VCR codec for studio application using quadtree structured binary symbols in wavelet transform domain

A hierarchical wavelet transform coding structure which satisfies the requirements of a high definition video cassette recorder (HD-VCR) for studio application in wireless environments is proposed. All of the coefficients in the transformed image are adaptively quantized and hierarchically converted into a single stream or binary symbols using the monotone decreasing property. The resulting bit stream goes through an adaptive arithmetic coder, and two-level control of the bit rate is performed so as to maintain a constant target bit rate. The proposed algorithm can be efficiently implemented with much reduced computing time for the real world application. It is verified by simulation that for a test sequence of images at least 4 dB of PSNR improvement can be achieved compared with other DCT-based schemes at a constant target bit rate, avoiding the blocking effect which would be impossible otherwise.

ゼロツリーにより画像の自己相似性を考慮したウェーブレットパケット符号化方式

This paper describes an image compression method associating a wavelet packet and a zerotree coding scheme. The wavelet packet, which gives a generalized multiresolution analysis, has been applied so as to reduce the correlation of the image pixels. To encode the adaptive wavelet packet coefficients, we apply the zerotree structure, which can reduce the correlation across the decomposed component images by exploiting the self-similarity among the components. In this case, the decomposition criterion with regard to each decomposition level is computed using a simplified local zerotree structure. If a target bit rate or a target distortion is decided, we can obtain the most suitable decompositions using an operation with fewer computations. Simulation results show that the proposed method has a better coding efficiency than the wavelet octave decomposition case by about 1 dB, and the JPEG baseline case by about 3 dB in PSNR at 0.4 bpp using the standard image “BARBARA”.

Video encoder architecture for MPEG2 real time encoding

A video encoder architecture for encoding digital video signals based on the MPEG2 video standard up to the slice level is described. A function specific architecture is implemented to increase the coding efficiency and reduce the silicon area for real time encoding. A hierarchical control concept is adopted and a three-stage pipeline encoding method is used in the macroblock coding to increase the flexibility of the encoding flow and reduce the design effort. Most of the computing power for the MPEG2 encoding algorithm is utilized in motion estimation, so a separate motion estimation module is used as a coprocessor. The motion estimation algorithm adopted is a full search with the search window in the range between +47 and -48 pels in the horizontal direction and between +15 and -16 pels in the vertical direction. Simulations on several video sequences with different target bit rates are evaluated. The results show that our implementation can achieve a video quality comparable to other off-line software simulation programs using exhaustive searches.

HIPERLAN: the High Performance Radio Local Area Network standard

The high performance radio local area network (HIPERLAN) standard is currently being developed by the European Telecommunications Standards Institute (ETSI). As well as providing a wired LAN substitute, with a target bit rate of 20 Mbit/s, the standard will provide for the creation of ad hoc networks, communication with mobile users, and access to interactive multimedia services. Radio spectrum has been recommended for HIPERLAN in the 5 GHz and 17 GHz bands. The constraints imposed by the nature of the microwave radio channel along with some of the main challenges in the design of the radio interface are described.

Bit rate control for hybrid DPCM/DCT video codec

This paper presents a simple approach to regulating the bit stream generated by the hybrid DPCM/DCT video codec so that the compressed bit stream at a variable rate can be transmitted over a fixed rate channel. Bit rate regulation is accomplished by appropriately quantizing the DCT coefficients where the quantization stepsize is obtained by multiplying a fixed weighting matrix by a scaling factor. For each frame, a single quantization scaling factor is determined by iteratively comparing the output bit rate with a target bit rate which is based upon the desirable bit rate, same code mode, frame complexity and scene changes. The iterative comparison guarantees a quantization scaling factor which results in a minimum accumulated bit rate difference from the target bit rate for each frame. The simulation results demonstrate that the fluctuation of the output bit rate can be kept within a narrow margin while maintaining the quality of the reconstructed frames at a relatively stable level.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Bit packing density of the BEAMOS target

BEAMOS, beam addressed metal oxide semiconductor, is an electron-beam-addressed semiconductor digital mass-memory device. Its operation is based on electron-beam writing of stored charge in an unstructured MOS layer and electron-beam reading of this stored charge through its effect on the surface-recombination velocity of the oxide silicon interface. The surface-recombination velocity controls the diffusion of electron-beam-generated carriers in the n layer of the np diode underlying the oxide layer. This control of carrier diffusion by surface-recombination-velocity patterns is the unique feature of the BEAMOS target concept. The data storage capacity of BEAMOS-type devices is limited by the electron-beam spot size and target construction. A model of the target resolution (bit packing density) is described which includes the effects of incident beam spot size, electron scattering in the target layers, and injected minority-carrier diffusion in the n layer of the target. Measurements of electron-beam scattering are summarized and applied to the writing and reading mechanisms of the target. The minority-carrier diffusion equation is solved by a relaxation method similar to the method of sources. This leads to a model for the target bit packing density, which includes both electron scattering and minority-carrier diffusion. For present BEAMOS targets, the dominant limitation is shown to be minority-carrier diffusion, which can be controlled by the n-layer thickness. Predictions of the model are compared with measurements on actual targets. The ultimate packing density of the concept is also discussed. Packing densities of more than 2×107 bits/cm2 have been demonstrated, and densities as high as 109 bits/cm2 may be possible.