Fast intra prediction mode decision for H.264/AVC video coding

Abstract

Intra coding is used for reducing the spatial redundancy in video coding. H.264 supports several macroblocks of predictions for intra coding such as luma block four 16×16 modes, nine 4×4 modes and chroma block four modes, which significantly improve intra coding efficiency, but increase the encoding complexity. In order to select the best mode, we need to calculate the cost of the various modes. In this paper, a fast intra prediction mode decision for H.264/AVC video coding is proposed. Based on Laplacian, this intra prediction mode decision detects edges and selects the best mode for the block. This mode decision can shorten the time to reduce the encoding time. The experimental results show that the proposed algorithm achieves an encoding time saving of 70% on average.     

Reversible Data Hiding Based on Run-Level Coding in H.264/AVC Video Streams

This paper presents a reversible data hiding (RDH) method, which is designed by combining histogram modification (HM) with run-level coding in H.264/advanced video coding (AVC). In this scheme, the run-level is changed for embedding data into H.264/AVC video sequences. In order to guarantee the reversibility of the proposed scheme, the last nonzero quantized discrete cosine transform (DCT) coefficients in embeddable 4×4 blocks are shifted by the technology of histogram modification. The proposed scheme is realized after quantization and before entropy coding of H.264/AVC compression standard. Therefore, the embedded information can be correctly extracted at the decoding side. Peak-signal-noise-to-ratio (PSNR) and Structure similarity index (SSIM), embedding payload and bit-rate variation are exploited to measure the performance of the proposed scheme. Experimental results have shown that the proposed scheme leads to less SSIM variation and bit-rate increase.     

Efficient rate control scheme using modified inter-layer dependency for spatial scalability

Scalable video coding extension has been added to H.264AVC to support compression and encoding of multiple resolution video sequences, having different frame rates and fidelities in a single bit stream. The motion vectors and the residual data of the enhancement layers are derived from up-sampling the co-located macroblock (MB) of the base layer. The peak signal to noise ratio (PSNR) across the enhancement layers is degraded as up-sampling introduces distortion of high-frequency components. In this paper, a spatial-resolution-ratio-based MB mode decision scheme is proposed for spatially enhanced layers. The scheme uses the motion estimated at the base layer, to encode the respective MBs in the enhancement layers. The spatial–temporal search schemes at the enhancement layers are used to derive motion vectors and residues that are encoded using a quantization parameter obtained using independent rate control (IRC) scheme. The IRC from the prior art is modified to achieve better rate control per layer by recursive updates for mean absolute difference values of each basic unit. Proposed modified inter-layer dependency shows improvement in the PSNR for enhancement layers while the updated IRC enforces better IRC for all the layers.     

Adaptive Order Cross–Square–Hexagonal search and fuzzy tangential-weighted trade-off for H.264 in motion estimation

In recent years, various algorithms have been proposed to attain low computational complexity in motion estimation of the image sequence coding based on block matching. This paper presents an Adaptive Order Cross–Square–Hexagon (AOCSH) search algorithm, which employs a smaller cross-shaped pattern before the first step of a square pattern and replaces the square-shaped pattern with the hexagon search patterns in subsequent steps. The proposed search patterns aid in finding the best matching block, without much consideration of the vast number of search points. Here, fuzzy tangent-weighted function is also proposed to evaluate the matching points using the rate and the distortion parameters. The proposed methods are effectively applied to the block estimation process to handle the objectives of visual quality and distortion. The performance of the proposed AOCSH approach is compared to the existing methods, such as AOSH, H.264 and elastic models, using the structural similarity index (SSIM) and the peak signal to noise ratio (PSNR). From the analysis, it can be seen that the proposed approach attains the maximum SSIM of 0.99 and maximum PSNR of 40. 92 dB with reduced computation time of 3.28 s.     

Intra mode selection in downsizing video transcoder based on H.264

An intra mode selection scheme is proposed in this work, which supports both downsizing transcoding and re‐quantization transcoding simultaneously. In the proposal, a total number of nonzero coefficients in precoded frame is used as criterion and a thresholding method is applied to select intra macroblock mode in re‐encoder. To calculate this threshold, which is related to re‐quantization parameter (denoted as Q_r), we propose a Th_I‐Q_r model which includes direct method and percentage I16MB method. In the former, an exponent model is proposed to describe relationship between the threshold and the Q_r; while in the latter, the threshold Th_I is converted into percentage of macroblocks with I16MB mode in the downsized frame (denoted as per_16), and relationship between the per_16 and the Q_r is also modeled as an exponent function. Then the two exponent models are all converted into linear regression model, and least square estimation is used to estimate the parameters of the models. Furthermore, if I4MB mode is selected for one macroblock, the intra prediction modes in precoded frame are utilized to select prediction mode for every 4 × 4 block of the macroblock in downsized frame to reduce computational complexity. We compared rate distortion performance and computational complexity of the proposed method with rate‐distortion optimization method. Simulation results demonstrate that on the precondition of compression performance of the proposal being close to the results of the rate‐distortion optimization method, the proposed method can save up to 30 and 80% in total encoding time and mode decision time, respectively. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 340–349, 2009     

基于编码模式的H.264/AVC视频信息隐藏算法

本文提出一种基于编码模式的H.264/AVC信息隐藏方法,通过调制某些宏块的编码模式,分别在Ⅰ帧、P帧和B帧中嵌入隐秘信息.对帧内4x4预测模式的宏块,是通过调整宏块中某个4×4块的编码模式嵌入隐秘信息;对P帧和B帧其它类型的宏块,则是通过调整宏块的编码模式嵌入隐秘信息,模式调整后对宏块做了优化处理.在模式调制过程中引入率失真代价,取得了较好的率失真平衡,减小了隐秘信息嵌入后对视频质量和视频码流的影响.该算法可以实现隐秘信息的快速提取,满足视频实时处理的要求,实验仿真结果证明了该算法的有效性.     

一种基于HVS特性的视频质量评测方法

本文针对视频质量的评测应用,对传统峰值信噪比(PSNR)算法加以改进.通过在视频帧内图像和帧间图像的处理过程中引入人眼视觉系统(HVS)的主要特性,克服传统PSNR算法在序列质量检测应用方面的缺陷.方法在帧内图像处理上利用人眼对边缘轮廓失真具有较强敏感性的特点,设计了基于图像边缘的检测方案以提高对典型空域失真的检测性能;在帧间图像处理上,通过测量帧间时域能量的变化,获得序列在时域轴上的典型特征,并据此对空域检测结果进行修正.通过上述改进,算法能在保持传统PSNR算法简易性的同时,提升其检测结果与主观感受的相关性;同时算法的计算量并不复杂,易于在检测设备中实现系统集成     

A fast distance-based mode decision algorithm for 4×4 blocks in H.264/AVC intra prediction

H.264/AVC employs rate-distortion optimisation technique to achieve high coding efficiency, but it is computing-intensive. This letter presents a fast distance-based mode decision algorithm for 4×4 blocks in H.264/AVC intra prediction. Firstly, the distance between neighbouring blocks of the current block is defined. Then, the modes around up and left modes are selected as the candidate modes if the distance is small, otherwise early termination technique is used to further reduce the complexity, and either four or more modes are chosen based on the difference of rate-distortion optimisation cost. Experimental results show that our proposed algorithm can predict a 4×4 intra block by only about 3·52 modes and reduce the total encoding time by about 31·37% with negligible peak signal-to-noise ratio decrement and bit rate increment.     

一种基于视觉感知的H.264码率控制算法

针对目前视频编码标准H.264的码率控制算法未考虑人眼视觉感知、易导致编码后视频图像质量波动的不足,提出了一种基于视觉感知的H.264码率控制算法.首先,设计了像素域的恰可察觉失真模型.在此基础上,根据各帧的恰可察觉失真的大小进行帧层比特分配.其次,建立了基于结构相似度的率失真模型,并采用此模型设计了基本单元层（basic unit,BU）的比特分配方案.最后结合二次速率-量化模型得到量化参数.实验结果表明,该算法与目前H.264中典型的码率控制算法相比,错误率降低了0.2％.     

基于H.264的自适应可伸缩编码研究

为了更好地适应网络及终端的多样性,本文针对基于H.264的可伸缩编码,提出了一种基于运动区域的自适应可伸缩编码的优化方案.该方案根据基本层的运动信息及编码模式自动提取图像的运动感兴趣区域,并以独立片的形式对其进行时间,空间和质量上的可伸缩编码,实现选择性增强.实验结果表明,该方案不仅能大幅降低编码复杂度,而且使增强层码流集中包含运动区域信息,从而提高运动区域的重建质量及整幅图像的主观质量.     

一种用于H.264数据分类的自适应的不平等错误保护策略

主要从较新的H．264视频压缩标准出发,提出了一种适用于视频流在包丢失的Internet上传输的基于数据分类的自适应不平等保护策略。实验证明,与传统方法相比,该方法实现了在一定包丢失概率下质量与码率的较好权衡,并且获得了较好的错误鲁棒性能。     

Video enhancement through image registration based on structural similarity

Abstract

It is commonly known that the mean square error (MSE) does not accurately reflect the subjective image quality for most video enhancement tasks. Among the various image quality metrics, structural similarity (SSIM) metric provides remarkably good prediction of the subjective scores. In this paper, a new registration method based on contribution of structural similarity measurement to the well known Lucas–Kanade (LK) algorithm has been proposed. The core of the proposed method is contributing the SSIM in the sum of squared difference of images along with the Levenberg–Marquardt optimisation approach in LK algorithm. Mathematical derivation of the proposed method, based on the unified framework of Baker et al., is given. The proposed registration algorithm is applied to a video enhancement successfully. Various objective and subjective comparisons show the superior performance of the proposed method.     

支持ROI优先编码策略的自适应码率控制算法

在低码率视频通信中,感兴趣区(ROI)优先编码策略有助于图像主观质量的提高。本文提出了一种简单有效的ROI提取方法,并根据图像复杂度和运动信息给ROI和非感兴趣区(NROI)分别分配码流。对于ROI的编码范畴,文中推导出了高低码率的判断准则,使算法可以自适应地选择码率模型,减少了码率控制误差。另外,本文采用的宏块层编码顺序方案提高了图像的客观质量。实验结果表明,与TMN7和TMN8的算法相比,本文算法能将码率更稳定地控制在目标码率附近,减少了跳帧;图像的客观和主观质量都有了明显的提高。     

Optimal Mode Decision Method for Interframe Prediction in H.264/AVC

Studies show that encoding technologies in H.264/AVC, including prediction and conversion, are essential technologies. However, these technologies are more complicated than the MPEG-4, which is a standard method and widely adopted worldwide. Therefore, the amount of calculation in H.264/AVC is significantly up-regulated compared to that of the MPEG-4. In the present study, it is intended to simplify the computational expenses in the international standard compression coding system H.264/AVC for moving images. Inter prediction refers to the most feasible compression technology, taking up to 60% of the entire encoding. In this regard, prediction error and motion vector information are proposed to simplify the computation of inter predictive coding technology. In the initial frame, motion compensation is performed in all target modes and then basic information is collected and analyzed. After the initial frame, motion compensation is performed only in the middle 8×8 modes, and the basic information amount shifts. In order to evaluate the effectiveness of the proposed method and assess the motion image compression coding, four types of motion images, defined by the international telecommunication union (ITU), are employed. Based on the obtained results, it is concluded that the developed method is capable of simplifying the calculation, while it is slightly affected by the inferior image quality and the amount of information.     

JPEG2000的一种编码前码率分配算法

针对JPEG2000推荐的码率分配算法导致的计算冗余多、编码速度慢并且编码缓存大的不足,本文提出一种编码前最优分配码率的方法以提高JPEG2000的编码速度.该方法通过对小波系数失真模型的率失真理论分析,得出在总码率限制的情况下,使得总体视觉加权失真最小的最佳码率分配准则,并根据该准则给出可实现的码率分配算法.实验表明,该方法可以实现精确有效的编码前码率预分配,做到了"所编即所需",加速了JPEG2000编码,满足高速编码和低缓存需求的要求.     

Classified vector quantization of LPC parameters

Abstract

To achieve high coding efficiency, modern speech coders adopt hybrid coding approaches, which utilize different coding mechanisms for various classified speech segments. With known voiced/unvoiced detection, in this paper, a classified LPC quantization (CLPQ) scheme is presented to effectively encode line spectral frequencies (LSF). The proposed CLPQ scheme improves the performance of the classified LSF vector quantizer, which adopts two LSF codebooks derived separately from voiced and unvoiced speech frames. With an objective spectral distortion measure, the CLPQ scheme successfully reduces the bit rate by about 1 bit/frame. Many classified LSF quantizers with different codebook structures and bit rates were evaluated. It would be helpful to design a classified LSF quantizer, which arrives at a compromise between distortion, bit rate and computational complexity.     

基于CSSIM的印刷品图像质量评价方法

目的为解决印刷品图像质量评价过程中主观与客观评价结果不一致的问题,以印刷制品为研究对象,基于Contourlet变换提出一种改进的图像质量评价算法。方法在Contourlet域进行多尺度、多方向分解,以获取不同尺度的图像特征。将结构相似度直接应用于各Contourlet分解频带,得到不同频带的结构相似度;对不同频带的结构相似度求加权和,进而获得整幅图像的结构相似度,即图像的最终评价指标。结果以ISO标准测试图像为基础进行实验研究的结果表明,所述方法的综合评价效果最理想,与主观评价的一致性最好。结论基于Contourlet变换域结构相似度的图像质量评价方法能够更好地评价图像质量,符合人眼的视觉特性,可用于印刷品图像处理。     

基于HSI颜色空间噪声检测的彩色图像去噪算法

目的为了有效去除彩色图像中的椒盐噪声,提高彩色图像质量。方法采用椒盐噪声检测和中值滤波相结合的方法,提出一种基于HSI颜色空间噪声检测的彩色图像去噪算法。将图像转换到HSI颜色空间,根据椒盐噪声在S通道具有极大值或极小值的特点判断出可疑椒盐噪声的位置,在H通道、I通道将可疑椒盐噪声分为噪声点和有用信号,对检测出的噪声像素进行中值滤波去噪。结果采用文中算法去噪后,验证图像主观评价值(Z)为1.30,平均PSNR为37.54,SSIM为0.99,Entropy为7.31,在主客观评价上优于现在常用算法。结论文中提出算法可以为彩色图像椒盐噪声的去噪提供理论基础,具有一定的实际应用价值。     

Objective analysis and bit rate analysis of HEVC compressed 4D-fMRI images

Medical imaging and clinical diagnostics are complementary to one another since their analysis is typical and contains critical information. The growing volume of data has become one of the biggest challenges, as the acquisition of medical modalities is currently having high resolution from the improved and efficient machines (3 to 7 T or more). Moreover, image and video compression is a need with the consideration that there should not be any gap for losing the important information. Less bitrate requirement with high compression ratio without sacrificing important detail is a challenge these days. The current study, is dealing with the compression of 4D-functional medical resonance images (fMRI) with a codec, that is, high-efficient video coding (HEVC/H.265) and its objective analysis along with its predecessor that is advanced video coding (AVC/H.264) and with VP8 (WebM Project of Google) reported here. Further, the bit rate analysis that has been conducted, also accounts in conjunction with the bitrate investigation, which is an imperative perspective vital for the telemedicine field. The simulation results reported here represents the compression ratio (CR = 118.23:1) with HEVC/H.265 codec over the compression ratio (CR = 20.52:1) provided by AVC/H.264 and VP8 (CR = 78.29:1). There has been significant improvement observed in alignment of the peak signal-to-noise ratio (APSNR), structural similarity (SSIM), and mean squared error (MSE) metrics. Overall, the performance of the anticipated technique is satisfactory for the forthcoming telemedicine or clinical use.     

H.264帧间预测模式选择算法研究与优化

H.264出色的压缩性能是以计算复杂度的提高为代价的。使用快速帧间预测模式选择算法是提高H.264编码速率的一种有效方法。文中对H.264帧间预测模式选择的复杂度进行分析之后，对基于X264参考程序的帧间预测算法提出改进，测试结果显示这种改进能将H．264的编码速率提高55％左右。