Distortion Optimization Research Articles

Joint Rate Control for Distortion Optimization in Video Networks

A class of video network applications require fixed video quality, which leads to variable rate allocation. Conventionally rate control algorithms have been proposed for steady state performance. However, variable rate allocation requirement results in significant transients. This paper proposes a proportional-integral-derivative (PID) based rate controller, which not only provides desired steady state performance but also gives an improved transient performance. An augmented Lagrangian approach is used to design PID based rate controller and its stability is proved using Lyapunov stability theory. Numerical results show the performance improvement achieved by the proposed approach.

DCT 계수를 이용한 고속 인트라 코딩

The RDO (Rate Distortion Optimization) process of HEVC results in good coding efficiency, but relatively requires much encoding time. In order to reduce the encoding time of RDO process, this paper proposes a method of fast intra prediction mode decision using DCT coefficients distributions and the existence of DCT coefficients. The proposed fast Intra coding sets the number of intra prediction mode candidates to three(3) from the RMD (Rough Mode Decision) process in HM16.0 reference SW and reduces the number of candidates one more time by investigating DCT coefficients distribution. After that, if there exists a quantized DCT block having all zero coefficient values for a specific candidate before the RDO process, the candidate is chosen without the RDO process. The proposed method reduces the encoder complexity on average 46%, while the coding efficiency is 2.1% decreased compared with the HEVC encoder.

An early split and skip algorithm for fast intra CU selection in HEVC

The rapid development and increase of multimedia applications, as well as the demand for higher video-quality services at restricted resources such as storage capacity, transmission bandwidth and power consumption, has brought the urgent need for more efficient video compression techniques. The new video coding standard high efficiency video coding (HEVC) has a significant superiority over its predecessor advanced video coding (AVC). HEVC is reported to halve the bit rate with the same visual quality, or a better quality with the same bit rate when compared with AVC. Beside other improvements, HEVC significantly gets its power from the use of dynamic hierarchical quad-tree structure by partitioning the frames into smaller regions called coding units (CU), by means of a rate---distortion optimization process. However, this improvement yields to a dramatic increase of high computational complexity and increased encoding time, which primarily restricts its adaptation in real-time applications. In this paper, we proposed an early CU determination algorithm for fast encoder realization to reduce the encoding time which is the most important part of the standard standing for development. The experimental results show that the proposed algorithm has approximately 45 % encoding time saving with a 4.6 % bit-rate increment, on average.

Perceptual rate distortion optimisation for video coding using free‐energy principle

In this Letter, a novel perceptual rate distortion optimisation (RDO) method based on the free-energy principle is proposed. The human visual system is not sensitive to the distortion hidden in disorderly regions due to the disorderly concealment effect, i.e. the free-energy principle. Based on the human visual perception, we introduce a free-energy based just-notable-difference (FEJND) model into the RDO process to adaptively adjust the Lagrange multiplier and quantisation parameter values. Experimental results show that the proposed method conceals more distortions in disorderly regions and achieves 8.46% bit-rate reduction over the JM reference software at the same perceptual quality level.

A new encryption-then-compression algorithm using the rate–distortion optimization

Compressing the encrypted data remains a challenging task in many service-oriented scenarios like distributed processing and cloud computing. This paper presents a new encryption-then-compression scheme using the rate–distortion optimization. The original image is first decomposed via the lifting scheme (LS) into a wavelet pyramid, and the coarsest and detail subbands are then encrypted with the stream and permutation ciphers, respectively. The encrypted coarsest subband is compressed using a lossless technique by the third party like network or storage service providers, while the scrambled detail subbands are compressed through the successive quantization and adaptive arithmetic coding (AC), in which quantization steps are optimized with the rate–distortion theory. Upon receiving the encrypted and compressed sequence, the receiver conducts the sequential decompression, decryption, and inverse LS to reconstruct the original image. Security analysis shows that the proposed method is able to achieve a reasonable high-level security. Experimental simulations demonstrate that the proposed scheme has a low computational cost, and it outperforms the pixel-domain permutation-based prior art and obtains the rate–distortion performance comparable to the conventional JPEG with original, unencrypted images as input.

Intra Prediction Mode Decision for H.264

Digital video compression has become an integral part of the way we create, consume visual information and communicate, over the last few decades. A robust technique of compression is proposed in this paper for video compression. Reduction of irrelevant or redundant data in order to save the storage space requirements and processing time is nothing but compression. Here H.264/AVC (Advance Video Coding) video coding standard is used for compression. Where I-frames are divided into different macro blocks (MB) and each MB is efficiently compressed using 4 x4 and 16 x16 blocks in H.264/AVC intra prediction. Choosing one of 9 prediction modes for each 4 x4 block with reduced time and less complexity is still a bottleneck. In this paper a gradient based fast intra prediction mode selection method for 4x4 and 16x16 is proposed. The proposed method divides an input frames into variable block sizes based on the texture and performs few mode examinations based on the gradient direction in the given slice. Respective best mode with minimum cost is selected using sum of absolute difference (SAD) and rate distortion optimization (RDO). This process is carried for all the video input frames. Each compressed video frames are combined finally to get a compressed video output.

Human centered perceptual adaptation for video coding

Traditional visual saliency based video compression methods try to encode the image with higher quality in the region of saliency. However, the saliency feature changes according to persons, viewpoints, and distances. In this paper, we propose to apply a technique of human centered perceptual computation to improve video coding in the region of human centered perception. To detect the region of interest (ROI) of human body, upper body, frontal face, and profile face, we construct Harr and histogram of oriented gradients features based combo of detectors to analyze a video in the first frame (intra-frame). From the second frame (inter-frame) onward, the optical flow image is computed in the ROI area of the first frame. The optical flow in human centered ROI is then used for macroblock (MB) quantization adjustment in H.264/AVC. For each MB, the quantization parameter (QP) is optimized with density value of optical flow image. The QP optimization process is based on a MB mapping model, which can be calculated by an inverse of the inverse tangent function. The Lagrange multiplier in the rate distortion optimization is also adapted so that the MB distortion at human centered region is minimized. We apply our technique to the H.264 video encoder to improve coding visual quality. By evaluating our scheme with the H.264 reference software, our results show that the proposed algorithm can improve the visual quality of ROI by about 1.01 dB while preserving coding efficiency.

Hash-Based Block Matching for Screen Content Coding

By considering the increasing importance of screen contents, the high efficiency video coding (HEVC) standard includes screen content coding as one of its requirements. In this paper, we demonstrate that enabling frame level block searching in HEVC can significantly improve coding efficiency on screen contents. We propose a hash-based block matching scheme for the intra block copy mode and the motion estimation process, which enables frame level block searching in HEVC without changing the HEVC syntaxes. In the proposed scheme, the blocks sharing the same hash values with the current block are selected as prediction candidates. Then the hash-based block selection is employed to select the best candidates. To achieve the best coding efficiency, the rate distortion optimization is further employed to improve the proposed scheme by balancing the coding cost of motion vectors and prediction difference. Compared with HEVC, the proposed scheme achieves 21% and 37% bitrate saving with all intra and low delay configurations with encoding time reduction . Up to 59% bitrate saving can be achieved on sequences with large motions.

A Gradient Intensity-Adapted Algorithm With Adaptive Selection Strategy for the Fast Decision of H.264/AVC Intra-Prediction Modes

H.264/Advanced Video Coding (AVC) is well known for its superiority of finding an optimal tradeoff between the visual quality and the bit-rate expense. Nevertheless, the highly complex procedures of finding an optimal intra- or inter-prediction mode can degrade the run-time performance of the coding process. To speed up the run-time performance during the encoding of H.264/AVC intra-prediction mode, we apply in this paper a simple yet effective gradient evaluation approach so that the texture orientation inside the coding block can be evaluated efficiently. Moreover, we propose an adaptive selection strategy in this paper so that only a subset with a variable number of the intra-prediction modes will be sent for the rate–distortion optimization process. With the proposed gradient evaluation and adaptive selection strategy, a noticeable speedup on the run-time performance can be achieved with only a minor degradation on the visual quality and the bit-rate expense. When compared with the existing state-of-the-art fast decision algorithms, a significant improvement over prior arts on the proposed cost performance metric can be obtained, which demonstrates the superiority of the proposed approach.

Optimization of spectral distortion in a ytterbium-doped mode-locked fiber laser system

A method for optimizing the spectral distortion of an ultrafast pulse in a polarization-maintaining picosecond linear-cavity fiber laser with a one-stage fiber amplifier is proposed and demonstrated. The mechanism of control of the spectral distortion in the fiber system has been investigated. The experimental and theoretical results illustrate that the filtering effect of a fiber Bragg grating can effectively decrease the spectral oscillatory distortion accumulated by self-phase modulation. Injected into a Nd:YAG regenerative amplifier, the ultrafast pulse could produce high pulse energy of 1.2 mJ at a repetition rate of 1 kHz.

Two stage fast mode decision algorithm for intra prediction in HEVC

High efficiency video coding (HEVC) standard, introduced by the joint collaborative team on video coding (JCT-VC), is the newest international standard for video compression. This standard provides more compression and better video quality, compared with the previous standards such as H.264/AVC. The higher compression efficiency in HEVC is achieved at the cost of increasing the computational load. Intra prediction unit is among the high computational stages in the HEVC encoder. There are proposed 35 intra prediction modes in HEVC, to improve the compression efficiency. To reduce the computational load of intra prediction, HEVC uses a preprocessing step, called Rough Mode Decision (RMD). A number of best prediction modes are selected by the RMD stage and then, using Rate Distortion Optimization (RDO) process, the encoder selects the best prediction mode among them. In this paper a two stage algorithm is proposed for fast intra mode decision in HEVC encoder, in the first stage of our proposed algorithm the number of the tested modes in RMD is reduced from 35 to 19. In the second stage, the number of the tested modes in the RDO process is reduced as well. In order to evaluate the performance of the proposed method two encoding profiles, main and main10 were used in the experiments. Experimental results indicate that the proposed method achieves 14.4 and 7.2 % reduction in the encoding time compared with the HEVC reference software in all intra-main and all intra-main10 configurations, respectively. Meanwhile, it imposes minimum reduction in the coding efficiency among the compared methods.

Depth Map Coding Using Histogram-Based Segmentation and Depth Range Updating

In texture-plus-depth format, depth map compression is an important task. Different from normal texture images, depth maps have less texture information, while contain many homogeneous regions separated by sharp edges. This feature will be employed to form an efficient depth map coding scheme in this paper. Firstly, the histogram of the depth map will be analyzed to find an appropriate threshold that segments the depth map into the foreground and background regions, allowing the edge between these two kinds of regions to be obtained. Secondly, the two regions will be encoded through rate distortion optimization with a shape adaptive wavelet transform, while the edges are lossless encoded with JBIG2. Finally, a depth-updating algorithm based on the threshold and the depth range is applied to enhance the quality of the decoded depth maps. Experimental results demonstrate the effective performance on both the depth map quality and the synthesized view quality.

A Novel Image Compression Algorithm Based on Multitree Dictionary and Perceptual-based Rate-Distortion Optimization

This paper presents a novel block-based image coding algorithm which applies a tree-structured multitree dictionary and a perceptual-based rate distortion optimization scheme. While multitree dictionary is employed to support a very large number of different tilings, perceptual-based rate distortion optimization utilizes the SSIM metric, instead of popular MSE metric, to allocate bit rate according to human visual system. Experimental results show that our proposed method outperforms many existing techniques in both subjective and objective image quality measures.

Fast TU size decision algorithm for HEVC encoders using Bayesian theorem detection

The emerging internationalhigh efficiency video coding (HEVC) uses variable block-size transform coding of the prediction error residual. The residual block is partitioned into multiple square transform units. The supported transform unit (TU) sizes are 4×4, 8×8, 16×16, and 32×32. The optimal TU size is chosen based on rate distortion optimization techniques. Variable TU sizes have a coding performance superior to the traditional fixed-block-size transform. Meanwhile, it causes high computational complexity at the encoder. In this paper, we propose an early termination algorithm of TU size decision for HEVC encoders. The proposed method uses the Bayesian decision theory and the correlation between the variance of residual coefficients and the transform size to reduce the number of candidate transform sizes for a given block. Simulation results show that the proposed algorithm can save 30–46% of transform processing complexity with negligible loss of coding efficiency.

Randomized Quantization and Source Coding With Constrained Output Distribution

This paper studies fixed-rate randomized vector quantization under the constraint that the quantizer's output has a given fixed probability distribution. A general representation of randomized quantizers that includes the common models in the literature is introduced via appropriate mixtures of joint probability measures on the product of the source and reproduction alphabets. Using this representation and results from optimal transport theory, the existence of an optimal (minimum distortion) randomized quantizer having a given output distribution is shown under various conditions. For sources with densities and the mean square distortion measure, it is shown that this optimum can be attained by randomizing quantizers having convex codecells. For stationary and memoryless source and output distributions a rate-distortion theorem is proved, providing a single-letter expression for the optimum distortion in the limit of large block-lengths.

Fast intra mode decision algorithm for HEVC based on dominant edge assent distribution

As the latest video coding standard, high efficiency video coding (HEVC) is a successor to H.264/AVC. To improve the coding efficiency of intra coding, HEVC employs a flexible quad-tree coding block partitioning structure and 35 intra prediction modes. The optimal prediction mode is selected through rough mode decision (RMD) and rate distortion optimisation (RDO) process. Due to the huge search space of all of the possible depth levels (CU sizes) and intra prediction modes, intra coding of HEVC is a very time-consuming and complicated process, which limits the application of HEVC. In order to reduce the intra coding complexity, we propose a fast mode decision algorithm for HEVC intra prediction which is based on dominant edge assent (DEA) and its distribution. The four DEAs in the directions of degree 0, 45, 90 and 135 are computed first; then, the dominant edge is decided according to the minimum DEA. Next, a subset of prediction modes in accordance with the dominant edge is chosen for the RMD process. The rule is as follows: When the standard deviation of DEA is distinctly small, we skip the RMD process and take the direct current (DC) mode and planar modes as the candidate modes for the RDO process; when the minimum DEA is distinctly small, we select seven modes as the candidate modes for the RMD process; otherwise, we select 11 modes for the RMD process. Lastly, the prediction unit (PU) size-based number of RDO candidate modes (3 for PU size 4?×?4 and 8?×?8 and 1 for the other PU sizes) is modified according to experimental analysis. Compared with HM 9.1, Shen's proposal and da Silva's proposal, which are two state-of-the-art fast intra mode decision algorithms, the experimental results reveal that the proposed algorithm can save 36.26, 13.85 and 20.81 % coding time on average with a negligible loss of coding efficiency, respectively.

Fast Intra Mode Decision in High Efficiency Video Coding

In this paper a coding unit early termination algorithm resulting in a fast intra prediction is proposed that terminates complete full search prediction for the coding unit. This is followed by a prediction unit mode decision to find the optimal modes HEVC encoder 35 prediction modes. This includes a two-step process: firstly calculating the Sum of Absolute Differences (SAD) of all the modes by down sampling method and secondly applying a three-step search algorithm to remove unnecessary modes. This is followed by early RDOQ (Rate Distortion Optimization Quantization) termination algorithm to further reduce the encoding time. Experimental results based on several video test sequences for 30 frames from each test sequence show for HEVC a decrease of about 35%-48% in encoding, with negligible degradation in peak signal to noise ratio (PSNR). Metrics such as BD-bitrate (Bjontegaard Delta bitrate), BD-PSNR (Bjontegaard Delta Peak Signal to Noise Ratio) and RD plots (Rate Distortion) are also used.

Faster mode determination algorithm using mode correlation for multi‐view video coding

Multi-view video coding with a hierarchical B picture structure utilises intra-view and inter-view predictions to reduce the quantity of redundant information. The optimal coding mode is determined by exhaustively searching through all possible partition modes; however, a high degree of computational complexity is involved in such exhaustive searches. In this study, the authors statistically analyse the coding mode distribution in inter-view and intra-view and propose a fast mode decision algorithm to select the optimal mode in terms of rate–distortion optimisation. The probability density function of the rate-distortion cost and the degree of the homogeneity in motion are set as the multi-threshold in the algorithm to determine the optimal mode for base view coding. For the multi-view coding, the correlation of the modes in neighbouring views with similar regions is utilised to select the coding mode from the inter-view or intra-view predictions. The experimental results show that the encoding time for the base view and the multi-view is reduced by up to 85 and 69%, respectively, and the quality of the reconstructed video is nearly unchanged.

Study on the Construction of Linguistics Examination Database Based on Computer Network Technology

In this paper we use the VB software to programming the group program of tests, combined with neural network residual training principle, establish optimization design model of network examination database. We improve the English linguistics question bank based on computer network technology by using the program and the model, and set up the feedback system of students’ suggestion and Corporate Data Stores system of examination paper, and establish optimization model of network examination database. In order to verify effectiveness and reliability of network test optimization system, we optimize the network examination database of English Linguistics for three times, obtain the optimal distortion curve of test, and analyze optimized test scale. It provides technical support for the research of network English teaching.

Finite Element Modeling of Camber Evolution During Sintering of Bilayer Structures

The need for understanding the mechanisms and optimization of shape distortions during sintering of bilayers is necessary while producing structures with functionally graded architectures. A finite element model based on the continuum theory of sintering was developed to understand the camber developments during sintering of bilayers composed of La0.85Sr0.15MnO3 and Ce0.9Gd0.1O1.95 tapes. Free shrinkage kinetics of both tapes were used to estimate the parameters necessary for the finite element models. Systematic investigations of the factors affecting the kinetics of distortions such as gravity and friction as well as the initial geometric parameters of the bilayers were made using optical dilatometry experiments and the model. The developed models were able to capture the observed behaviors of the bilayers’ distortions during sintering. Finally, we present the importance of understanding and hence making use of the effect of gravity and friction to minimize the shape distortions during sintering of bilayers.