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％.     

基于自适应速率模型的低时延视频编码速率控制算法

针对实时视频通信具有的低时延特性,通过研究速率模型形状参数和图像内容之间存在的关系,提出了一种视频图像自适应速率模型,此模型较其它速率模型能够更好地拟合真实码率输出,使得基于该模型速率控制下的输出速率更加平稳。为了避免TMN8模型中使用宏块方差方法得到宏块量化步长所引入的计算量,在帧层一次计算得到视频图像的基本量化步长,并在宏块层对其进行简单调整,从而降低了系统的处理时延。仿真实验表明,此文提出的基于新模型的速率控制算法较TMN8在输出码率稳定性及系统时延上都具有较好的性能。     

基于二项式R-D模型的多视点视频码率控制算法

针对目前尚未深入研究多视点视频编码(MVC)码率控制的状况,在分析现有视频码率控制中率失真模型的不足和多视点视频编码的特点的基础上,提出了一种基于二次率失真(R-D)模型的多视点视频编码码率控制算法。该算法的核心是先根据视差预测和运动预测的结构关系,将所有图像分成6种类型的编码帧,并改进二项式率失真模型,然后根据已编码信息进行视点间、帧层、基本单元层比特分配与码率控制。实验仿真结果表明,与目前采用固定量化参数的JVT的MVC相比,该算法能够有效地控制多视点视频编码的码率,同时保持高效的编码效率。     

基于时域失真传递链的宏块级码率控制算法

x264是工业界性能优秀的H.264编码器,时域自适应码率控制算法(MacroblockTree,MBTree)对其性能提升有很大贡献.该算法通过构造时域失真传递链,估算可以反映当前宏块被参考频度的传递代价ρ.再根据传递代价计算量化偏移量δ,实现码率的时域宏块级控制.然而,MBTree算法采用的δ-ρ模型是凭经验得出的,较为粗糙.针对这一问题,提出了一种基于R-D判据寻找性能最优δ-ρ模型的方法.实验证明采用本文模型后的MBTree算法,与之前相比可以获得最高0.14dB的结构相似度提升,或在相同结构相似度下,获得最高5.8%的码率节省量.     

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。     

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.     

基于码率预分配编码技术的高分辨率航测图像压缩

由于需要对大面阵航空CCD相机带来的庞大航测图像数据进行压缩,在研究多种图像压缩算法的基础上提出了一种基于比特位平面编码的码率预分配图像压缩算法(RPCA)。首先将图像进行多级整数小波变换,以去除图像像素之间相关冗余。根据率失真理论并结合各个子带对图像重建质量的重要性原则,编码前事先确定每个子带在总码率一定的情况下各个子带在实际编码中应当分配的码率大小,再利用自适应MQ算术编码对每个子带比特平面进行熵编码,从而得到细致的嵌入式码流。实验仿真结果表明,该RPCA码率分配精准,图像压缩质量与JPEG2000标准相当,且支持无损到有损的任意倍率图像压缩,但复杂度低于JPEG2000标准,适合于硬件的高速实现。     

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.     

一种多视点视频编码的宏块模式快速选择新算法

分析了多视点视频编码中宏块模式的选择情况,提出了顺序可选宏块模式集的概念.比较分析了率失真代价最优宏块模式和最省时间可选宏块模式的搜索过程,讨论了编码宏块模式为最省时间可选宏块模式对率失真性能的影响,并在此基础上提出了基于顺序可选宏块模式集的快速宏块模式选择算法.实验结果表明,所提出算法在基本保持率失真性能的情况下,能明显降低宏块模式选择的复杂度,编码速度比多视点视频编码校验模型提高3.2倍到5.8倍.     

一种基于小波子带熵的遥感图像压缩算法

提出了一种使用小波子带熵进行比特分配的遥感图像压缩算法.对遥感图像进行小波提升分解后,分析了各高频子带能量百分比及其熵的变化趋势,在此基础上提出了一种新的快速比特分配方法-使用子带熵进行比特分配.然后对各个高频子带进行均匀量化,量化后的数据采用比特平面编码.对最高比特平面只记录该比特平面中非零系数的坐标,其它比特平面采用行程编码和Huffman编码方法进行压缩.实验结果表明,纹理复杂以及相对平坦的遥感图像使用该算法压缩后都可以获得很好的重构图像质量,峰值信噪比均大于34dB,而压缩比则与图像的复杂程度有关.     

Dynamic resource allocation for supporting real-time multimedia applications in IEEE 802.15.3 WPANs

The IEEE 802.15.3 medium access control (MAC) protocol is an emerging standard for high-rate wireless personal area networks (WPANs), especially for supporting high-quality real-time multimedia applications. Despite defining quality of service (QoS) signalling mechanisms for interoperability between devices, IEEE 802.15.3 does not specify resource allocation algorithms that are left to manufacturers. To guarantee the QoS of real-time variable bit rate (VBR) videos and utilise the radio resource efficiently, the authors propose a dynamic resource allocation algorithm. The proposed bandwidth allocation algorithm is based on a novel traffic predictor. Recently, the variable step-size normalised least mean square (VSSNLMS) algorithm was employed for on-line traffic prediction of VBR videos. However, the performance of the VSSNLMS algorithm significantly degrades due to the abrupt traffic variation occurring at the scene boundary. To tackle this problem, the authors design a novel traffic predictor based on a simple scene detection algorithm and the VSSNLMS algorithm. Analyses using real-life MPEG video traces indicate that the proposed traffic predictor significantly outperforms the VSSNLMS algorithm with respect to the prediction error. The performance of the proposed bandwidth allocation algorithm is also investigated by comparing several existing algorithms. Simulation results demonstrate that the proposed bandwidth allocation algorithm surpasses other mechanisms in terms of channel utilisation, buffer usage and packet loss rate.     

Iterative bit and power allocation for multi-cell orthogonal frequency division multiplexing with minimum variance distortionless response beamforming

This paper develops bit and power allocation schemes with beamforming for multi-cell orthogonal frequency division multiplexing (OFDM) systems on uplink. The model of the multi-cell channel with frequency reuse is considered. The transmit signal from each mobile causes interference to the received signals of other base stations. The schemes aim to minimise the total mobile transmit power while satisfying the required data rate and the bit error rate (BER) of each mobile. The proposed schemes offer better performance than that of the fixed bit allocation method. The proposed distributed allocation scheme reduces computational complexity compared to the proposed centralised multi-user greedy method with insignificant performance degradation. The simulation results are presented to demonstrate the efficacy of the proposed schemes.     

Analysis of lossy to near-lossless compression of hyperspectral imagery using prediction and multi-stage vector quantisation

Compression of hyperspectral images on-board is being pursued diligently for the past decade due to the exhaustive applications in the arena of remote sensing. Compression algorithms have to be designed in the interest of using minimum number of bits to represent a pixel at the cost of maintaining the quality of the reconstructed signal. Referring to the above context, compression algorithm has been proposed based on multi-stage vector quantisation affirming a bit rate as low as possible, meanwhile preserving the quality of the signal. The spectral redundancy is well exploited in the pre-processing stage, the occurrence of which aids the functioning of vector quantisation, resulting in the lower bit rate in the subsequent stages of decorrelation. The proposed algorithm reforms the vector quantisation in terms of spectral distortion, complexity and memory requirements. The proposed strategy divulges with a peak signal to noise ratio of 82.55?dB and signal to distortion noise ratio of 92.23?dB.     

Intra mode decision and frame layer Lagrange multiplier adjustment scheme for H.264 based on structural similarity

H.264 takes rate distortion optimisation (RDO) technique to perform intra and inter mode decision and achieves higher coding efficiency, but the objective distortion metric such as mean square error (MSE) is employed in traditional RDO framework, which cannot acquire optimal subjective quality. In this paper, structural similarity (SSIM)-based subjective distortion is applied to RDO-based intra mode decision in H.264 I frame video coding, and a linear SSIM distortion model is firstly proposed and SSIM-based rate distortion cost function for intra mode decision is defined. Furthermore, a content adaptive frame layer Lagrange multiplier adjustment scheme is proposed to balance the tradeoff between rate and SSIM distortion better. Experimental results show that, the proposed method encodes image structural information more effectively and thus acquires better perceptual quality and subjective RDO performance compared with objective distortion-based RDO method. Under the same perceptual quality, our scheme achieves about 8·03% I frame bit rate reduction on average for various sequences over MSE-based RDO employed in JM reference software.     

卫星图像码率控制方法的改进

JPEG2000存在大量计算冗余和消耗较大内存资源的缺陷.为了适应实时性要求高和资源有限的卫星图像的传输,提出一种新的基于率失真斜率的卫星图像码率控制算法.本方法是根据编码块的有效位平面数大致呈下降趋势和率失真斜率的三个属性提出一个简单的公式,通过此公式求得的率失真斜率作为层1编码的门限值,丢掉小于此门限值的编码通道,然后在该值基础上层2计算最优率失真斜率和截断点以实现码率控制,因而不需要编码所有的编码通道.实验结果表明,在0.125 bpp 时,本算法的存储量约占 PCRD 存储量的33%,而信噪比保持不变.因此,本方法可以有效地提高卫星图像的编码效率.