H.264帧内预测宏块融合置乱技术安全通信研究

基于I,P,B帧中所有帧内预测宏块与整数离散余弦变换DCT(Discrete Cosine Transform)提出了一种融合加密方案。判断当前宏块的属性是帧内预测宏块,则将其DCT系数分层即宏块系数矩阵进行转置变换,获得16个新的4×4子宏块,用混沌系统产生的密钥序列置乱子宏块后再加密子宏块中的系数符号。实验结果表明,该融合加密方案不仅能有效防止块间相关性攻击和密钥攻击,同时也能满足视频的安全性和传输的实时性要求。     

基于H.264帧内预测宏块融合置乱技术的安全通信研究

基于I、P、B帧中所有帧内预测宏块与整数离散余弦变换DCT(Discrete Cosine Transform)提出了一种融合加密方案。判断当前宏块的属性是帧内预测宏块,则将其DCT系数分层即宏块系数矩阵做转置变换,获得16个新的4×4子宏块,用混沌系统产生的密钥序列置乱子宏块后再加密子宏块中的系数符号。实验结果表明,这种融合加密方案不仅能有效防止块间相关性攻击和密钥攻击,同时也能满足视频的安全性和传输的实时性要求。     

基于兰氏距离的H.264/AVC帧内快速算法

提出了一种帧内模式快速选择算法。利用宏块内部相邻像素值的差异判定宏块的类型,再进行Intra_4×4和Intra_16×16两种模式的快速选择。对于Intra_4×4模式,利用兰氏距离提取4×4块的纹理方向,根据纹理方向进行Intra_4×4模式的快速选择。实验结果表明,所提算法在峰值信噪比(PSNR)和码率变化不大的情况下,显著地提高了编码速度。     

一种新的H.264/AVC帧内模式快速选择算法

利用改进的模糊积分准则提前对宏块的类型进行判定,实现Intra_4×4和Intra_16×16模式的快速选择,对于Intra_4×4模式,采用改进的平方梯度法估计块的纹理方向,从而排除可能性小的预测模式,提高帧内编码速度.试验表明该算法在基本保持编码性能的同时,可显著降低帧内预测的复杂度.     

基于梯度方向算子的H.264帧内模式选择算法

提出梯度方向算子的概念,基于该算子提出了一种H.264帧内模式快速选择算法。本文首先应用梯度方向算子计算编码宏块中各4×4亮度子块的纹理特征和灰度起伏特征,根据这两种特征参量削减4×4帧内候选预测模式。通过统计宏块中各子块的4×4候选预测模式信息,结合梯度方向强度门限判别法削减宏块的16×16候选预测模式,通过率失真优化算法计算得到最优亮度预测模式。进一步根据亮度宏块和色度宏块的对应关系,在亮度候选预测模式的基础上对色度宏块候选预测模式进行削减,最后计算得到最优色度预测模式。该算法削减了50%以上的帧内预测模式,减少了帧内预测模式选择的运算量,实验表明,该算法能够在峰值信噪比和码流比特率变化轻微的前提下减少50%以上的运算量。      

适用于基本层的帧内快速编码算法

根据最新编码的特征,提出了一种适合于基本层的帧内快速编码方法。首先对每个宏块中的8×8的子块进行DCT变换,根据纹理复杂度进行块模式的选择,针对各个块模式采用不同的快速方向模式选择算法。根据各个块模式和纹理复杂度,采用不同的零块预先判决算法和及时终止策略。实验证明,该算法能够在保持恢复图像质量几乎不降的同时,速度能提高到2倍多。     

x264视频编码器中参数设置对编码效率影响的研究

x264是基于H.264/MPEG-4 AVC视频压缩标准的视频压缩编码器,它提供了很多可以设置的参数来控制其编码效率。不同的参数设置影响着编码时间,压缩后的视频大小和视频质量。文章分别比较和分析了一些编码参数,包括图像组、帧内预测的宏块分割、帧间预测的宏块分割、参考帧数目和像素精度对视频的平均每帧编码时间、平均每帧大小和平均峰值信噪比带来的影响。     

基于FPGA的二维DCT变换的实现

二维离散余弦变换(DCT)在图像处理和视频编码中起重要的作用。以MPEG 2全I帧编码为背景,在现场可编程门阵列(FPGA)上实现8×8像素的二维DCT变换。算法首先把8×8像素的二维DCT变换化简成8次一维DCT变换加上适当的蝶形运算和顺序重排操作。试验表明,方案可以只用一个一维DCT模块实现输入采样率为74.25MHz的二维DCT变换。     

一种快速、鲁棒的压缩视频光流场估计算法

该文针对视频运动特性的快速分析需求,提出了一种压缩域中的光流场估计算法。首先利用DCT变换后的两个AC系数估计出图像的空间偏导数,在此基础上再利用预测残差以及运动矢量对图像的时间偏导数进行估计。另外对编码过程中未进行前向运动预测的宏块特性进行了详细的分析,给出了这些宏块相对于前向参考帧的运动信息估计方法,并对时域不连续的图像块给出了一种修正的偏导数估计方法,以此解决遮挡、切换等现象。然后通过最小二乘法并结合图像的偏导数进行光流场估计。实验表明该方法在准确度上可以达到或超过像素域中的L-K估计方法,比起现有的压缩域估计方法也有一定提高,而在计算时间上相比像素域估计有了大幅度降低。     

一种基于纹理方向自适应预测和游程哥伦布编码的帧存无损压缩算法

为了进一步提高参考帧无损压缩的压缩性能,本文提出了一种基于纹理方向预测和游程哥伦布编码的帧存无损压缩算法.本算法首先采用双扫描和自适应预测的方法,按纹理方向,为每个像素选取最优的参考像素,并进行预测以获得预测残差;然后对预测残差进行哥伦布游程混合熵编码,从而提高了参考帧无损压缩的压缩性能.实现结果显示,与帧内预测哥伦布编码算法相比,本文算法不但平均压缩率提高了16%,而且降低了平均编码时间.     

基于块参考像素特征的快速帧内预测模式选择新算法

帧内预测是H.264采用的一种编码新技术。与以前的编码标准相比,H.264编码性能有了很大的提高,但同时编码复杂度和计算量也明显增加。该文研究了提高H.264编码速度的途径,着重分析了帧内预测模式快速选择的问题。经过分析发现,4×4亮度块的参考像素亮度值通常具有相似性,对应地,4×4亮度块的9种预测模式所得的预测结果也是相近的。根据4×4亮度块参考像素的这一特征,该文提出了一种基于4×4亮度块参考像素特征的快速帧内预测模式选择算法。实验结果说明了该文算法的有效性,与H.264编码器JM92相比,该算法的计算量减少了46%,而编码质量、PSNR和输出码率保持基本不变。     

An efficient macroblock-based diverse and flexible prediction modes selection for hyperspectral images coding

In this paper, an efficient macroblock-based diverse and flexible prediction modes selection algorithm is proposed for coding hyperspectral images, which is inspired by the prediction scheme of H264/AVC. Here, different modes are specified for the corresponding macroblocks (16×16 pixel regions of a band) of hyperspectral images other than the whole band image using only one reference band image for prediction. Only the 4×4 mode is employed for the intra-band prediction in view of the fact that correlation coefficients of pixels separated by not more than four pixels in the spatial domain are greater than 0.65 at most cases. The optimal reference band is determined by the fast reference band selection algorithm; thereafter, the best partition of the candidate macroblock in the optimal reference band is further selected for inter-band prediction of the current macroblock. Thus, the stronger correlation in the spectral direction or in the spatial domain is utilized for the prediction of the given macroblock. With a comparably low memory requirement, the prediction coding scheme is proposed to speed up the implemental process using the fast reference band selection algorithm, the integer DCT and the quantization, which just needs the multiplication and bit-shifts operations. Several AVIRIS images are used to evaluate the performance of the algorithm. The proposed scheme outperforms the state-of-the-art 3D-based compression algorithms at lower rates. Moreover, compared with the method by using all the prediction modes of H.264/AVC, about 80% encoding time can be saved by our method under the same experimental condition.     

Implicit Line-Based Intra 16×16 Prediction for H.264/AVC High-Quality Video Coding

In this paper, we propose an implicit line-based linear intra 16×16 prediction method for high-quality video coding. Typically, in H.264/AVC intra 16×16 vertical and horizontal prediction modes, 256 pixels in the current macroblock are predicted using 16 adjacent boundary pixels of reconstructed neighboring macroblocks. One problem of such a block-based intra prediction is that the prediction error increases as the distance between the reference and current pixels increases. Thus, the prediction accuracy of intra 16×16 vertical and horizontal modes is not sufficient for the mode decision stage. To ensure that the pixels are close to their predictor, we propose a new implicit intra prediction scheme, which makes full use of the correlation between lines instead of blocks. In the proposed method, we perform prediction, transformation, quantization, and reconstruction using the line-of-pixels (LOP) to improve the prediction accuracy. Experimental results show that the proposed algorithm provides an approximately 6.42?% bit-rate reduction compared to the H.264/AVC FRExt high profile, while maintaining the same decoding quality.     

快速帧内预测模式选择新方法

为了提高编码性能,H.264采用了RDO(率失真优化),但与此同时带来的是计算复杂度的增加.本文着重分析了H.264中快速帧内预测模式选择的问题.为了降低帧内预测模式选择的计算复杂度,提出了一种高效的快速帧内预测模式选择算法.首先,对Pan的基于边缘方向直方图的快速算法进行了改进,同时提出了基于参考象素特征的4×4快速帧内预测模式选择算法,并将两者进行了结合.实验结果表明,本文算法和H.264校验模型JM61相比,I帧编码时间降低61%~69%,而PSNR基本保持不变,输出码率仅略有增加;与Pan的基于边缘方向直方图快速算法相比,本文算法的I帧编码时间降低12%~33%,PSNR和输出码率均基本保持不变.     

A Fast Intra Skip Detection Algorithm for H.264/AVC Video Encoding

A fast intra skip detection algorithm based on the rate‐distortion (RD) cost for an inter frame (P‐slices) is proposed for H.264/AVC video encoding. In the H.264/AVC coding standard, a robust rate‐distortion optimization technique is used to select the best coding mode and reference frame for each macroblock (MB). There are three types of intra predictions according to profiles. These are 16×16 and 4×4 intra predictions for luminance and an 8×8 intra prediction for chroma. For the high profile, an 8×8 intra prediction has been added for luminance. The 4×4 prediction mode has 9 prediction directions with 4 directions for 16×16 and 8×8 luma, and 8×8 chrominance. In addition to the inter mode search procedure, an intra mode search causes a significant increase in the complexity and computational load for an inter frame. To reduce the computational load of the intra mode search at the inter frame, the RD costs of the neighborhood MBs for the current MB are used and we propose an adaptive thresholding scheme for the intra skip extraction. We verified the performance of the proposed scheme through comparative analysis of experimental results using joint model reference software. The overall encoding time was reduced up to 32% for the IPPP sequence type and 35% for the IBBPBBP sequence type.     

A Fast H.264 Intra Frame Encoder with Serialized Execution of 4 × 4 and 16 × 16 Predictions and Early Termination

This paper presents a fast H.264 intra frame encoder that processes a single macroblock of 1920 × 1080 size video in 334 cycles on average which is 20% faster than the previous best design. The speed-up is mainly achieved by early termination of either 4 × 4 intra prediction or 16 × 16 intra prediction. The executions of intra 4 × 4 and 16 × 16 predictions are serialized and the second prediction is terminated early by using the cost of the first prediction as the stop criterion. A simple and efficient algorithm by making use of spatial locality is proposed to select the mode that is processed first. To avoid the bubble cycles caused by this serialized execution of 4 × 4 and 16 × 16 predictions, the modified processing order presented in (Jung et al. 2008) is employed for intra 4 × 4 prediction in order to schedule dependent 4 × 4 blocks apart from each other. To further reduce the execution time of 4 × 4 prediction, neighboring pixels with the same value are grouped, and only one prediction mode in the group is evaluated. Experimental results show that the PSNR drop is 0.0619 dB and the bitrate increase is 0.842% when compared with the JM reference software. The additional hardware cost to support the proposed methods is less than eight thousand gates which are very small when compared with the hardware size of a whole intra frame encoder.     

H.264/AVC帧内4×4预测算法的高效流水线结构

H.264编码器中的帧内4×4预测部分具有严重的数据依赖性,它的硬件化设计很难采用流水线实现,从而导致关键路径很长,硬件利用率很低,成为H.264编码器设计中的一个瓶颈。针对这个问题,在不减少预测模式和不增加系统资源的前提下,提出了一种新的结构,它通过利用原始像素进行模式判决和利用重构像素进行帧内预测的方法,可以使帧内预测与重构循环完全流水线实现,基本上达到了100%的硬件利用率,而且没有明显的PSNR损失。所提出的硬件结构可在215个时钟周期内完成一个宏块的帧内4×4预测。用SMIC 0.13μm工艺库综合,结果显示该结构最高可运行在250 MHz,面积约为116千门,可支持4 096×2 160@30 f/s(帧/秒)视频序列的实时编码。     

一种H.264/AVC帧内4x4预测算法的高效流水线结构

H.264编码器中的帧内4x4预测部分具有严重的数据依赖性,它的硬件化设计很难采用流水线实现,从而导致关键路径很长,硬件利用率很低,成为H.264编码器设计中的一个瓶颈。针对这个问题, 在不减少预测模式和不增加系统资源的的前提下,本文提出了一种新的结构,它通过利用原始像素进行模式判决和利用重构像素进行帧内预测的方法,可以使帧内预测与重构循环完全流水线实现,基本上达到了100%的硬件利用率,而且没有明显的PSNR的损失。本文所提出的硬件结构可在215个时钟周期内完成一个宏块的帧内4x4预测。用SMIC 0.13um工艺库综合,结果显示该结构最高可运行在250M,面积约为116K门,可支持4096x2160@30fps视频序列的实时编码。     

基于FPGA和DSP实现的实时图像压缩

利用FPGA的并行分布流水特点,选用exilinx公司的50万门级芯片XCV400E,设计并实现CIF格式(352×288象素)图像实时DCT变换.该设计采用乒乓模式,只需设计一个快速算法模块(F×C^T)就解决了C×F×C^T的实现算法.当视频信号通过数字化后逐行输入FPGA,在行、场同步信号和采样时钟的控制下,每输入一组数据(8个),就进行行向量与C^T的矩阵乘运算(F×C^T),并将结果按转置方式保存,每输入一个数进行一次(1×8)×(1×8)矩阵运算,每行进行352×(1×8)×(8×8)次矩阵运算,其中44次(1×8)×(8×8)矩阵运算的结果需要按转置形式(H^T=(F×C^T)^T)存储;当输入下一组8行数据时,对该组数据进行与前述8行数据相同的矩阵运算,而对刚做完(F×C^T)运算的8行相应结果,则按正常顺序取出进行(H^T×C^T)运算,将结果按转置形式(G^T=C×H)输出.从而以实时流水的方式完成C×F×C^T运算.功能仿真、时序仿真和与TMS320C62X系统的成功对接验证了本设计及算法的正确性.