H．264/AVC解码器中去块效应滤波系统

本文介绍了H．264/AVC编解码器中块效应产生的原因及去块效应滤波的算法原理,提出了基于FPGA平台实现的H．264/AVC解码器中的去块效应滤波系统的硬件设计方法,并通过了仿真验证。     

一种快速去块滤波器结构

为了消除由于图象的预测,补偿,变换,量化引起得块效应,H.264/AVC标准中引入了去块滤波器.本文通过采用并行滤波,介绍了一种编解码环中快速实现去块滤波的滤波器结构,分析了该结构的滤波原理以及滤波过程中数据的存储.     

基于内容预分析的环路滤波算法

传统基于块的视频编码系统,在较低码率情形下进行编码时总会遇到块效应现象.针对H.264中去块滤波中边缘强度判断的高计算复杂度问题,提出了一种基于内容预分析的快速环路滤波算法.该算法在光流方程的基础之上,充分利用帧间的相关性,采用STGS(spatial-temporal gradient scale)图进行不同区域特征的划分,将块效应强度的划分由以像素为单位转化为以块为单位.实验结果表明,该算法大大降低了滤波算法的复杂度,且主观效果与H.264环路滤波系统的结果相当.     

H.264/AVC中去块效应环路滤波的VLSI实现

提出了一种适用于H.264编解码环内去块效应滤波的VLSI结构。利用相邻4×4像素块间数据的依赖关系合理组织数据存储顺序,并通过增加本地SRAM,使垂直滤波数据来自本地,读写外部SDRAM的次数减半,从而大大减少滤波处理的周期数。设置转置寄存器,水平滤波和垂直滤波可共用一维滤波电路。仿真结果显示,一个宏块去块效应滤波仅需要230个周期。在0.18μm工艺下,最大频率100M时,综合逻辑门数为14K。     

H26L去块滤波算法的优化

介绍了H26L区别于H263的新技术，着重分析了块效应产生的原因和优缺点．论述了去块滤波算法的实现、优化策略问题。最后以TMS320C6000系列DSP为例，讲述了如何利用C语言与汇编语言混合编程实现算法的优化。     

一种有效的空域去块效应算法

块效应在低比特率图像中极为明显,提出一种基于方块方向活动性的自适应空域去块效应算法。首先,通过对偏移的块进行块分析来对每一个块进行模式选择,接着通过1-D自适应平滑滤波器对块效应进行滤波。实验结果表明,与之前的算法相比,该算法有效的去除了块效应,信噪比有较大的提高,且算法同时处理了一个块中的竖直和水平边界,再跳入下一个块,大大减小了硬件实现时的内存空间。     

H.264去块滤波快速算法的设计与实现

介绍了H.264去块滤波的基本原理,并基于滤波强度预判的思想提出了一种快速去块滤波算法.通过软件实现验证了该算法在不影响解码图像质量的前提下较标准中的算法节省了约70%的滤波运算量,有效提高了软件解码器的运行速度,有助于H.264解码器实时应用的实现.     

针对MPEG的去块效应技术的研究及其VLSI实现

现今随着数据压缩的广泛应用,以及MPEG视频编解码的普遍使用,块效应噪声也随之而来。为了消除块效应、提高视频质量,许多去块效应的算法[2-12]被人们所提出,然而大部分算法的运算量都很大,不适合应用在视频处理芯片上。针对这个问题,H.-S. Kong等人[13]提出了一种新的自适应后处理算法,该算法既能有效消除块效应又大幅度地降低了运算量,然而对图像边缘信息保护不够。本文在H.-S. Kong等人[13]的算法的基础上,提出了一种针对MPEG视频流的去方块后处理方法。该方法以方块边缘（水平或垂直）附近各两个4×4区域作为滤波处理的分类依据,通过对该两个区域的像素点的值进行计算,将块边缘分为平滑渐变区域、亮度阶跃区域以及复杂纹理区域,并根据这三种区域对图像边缘信息影响程度的大小,而决定采取强滤波、弱滤波或者不滤波等处理方式。这种方法一方面较好地提取了块效应噪声,一方面又保护了图像的边缘信号,而且计算量较小,满足视频处理芯片低复杂度的去噪要求,通过VLSI实现后有着很好的应用前景。      

一种基于HVS和熵分析的盲测量去块效应算法

针对离散余弦变换基于块(DCT)图像压缩的方法通常因比特率低而导致块效应,结合人类视觉系统(HVS)和局部熵分析,提出一种新的去块效应算法。算法首先引入基于HVS的块效应可见度函数,其次通过设定阈值对需要处理的块进行熵的计算从而进行纹理块和平滑块分类,最后用自适应滤波器对不同类型块进行滤波。仿真结果表明,本文算法既能消除块效应,又能充分保护图像的纹理。     

一种改进的后处理去块滤波算法及其硬件实现

在已有去块滤波算法的基础上,根据人类视觉系统的特点,提出了一种改进的、以块边界为单位的后处理去块滤波算法。该算法能以较少的硬件资源得到更好的视觉效果。文中还给出了对应的硬件实现结构,在使用较少的存储单元情况下,仿真结果仍然可以达到H.264视频实时处理的频率要求。     

Improved Method for the Macroblock‐Level Deblocking Scheme

This paper presents a deblocking method for video compression in which the blocking artifacts are effectively extracted and eliminated based on both spatial and frequency domain operations. Firstly, we use a probabilistic approach to analyze the performance of the conventional macroblock‐level deblocking scheme. Then, based on the results of the analysis, an algorithm to reduce the computational complexity is introduced. Experimental results show that the proposed algorithm outperforms the conventional video coding methods in terms of computation complexity while coding efficiency is maintained.     

Design a deblocking filter with three separate modes in DCT-based coding

The reconstructed images from highly compressed data have noticeable image degradations, such as blocking artifacts near the block boundaries. Post-processing appears to be the most feasible solution because it does not require any existing standards to be changed. Markedly reducing blocking effects can increase compression ratios for a particular image quality or improve the quality of equally compressed images. In this work, a novel deblocking algorithm is proposed based on three filtering modes in terms of the activity across block boundaries. By properly considering the masking effect of the HVS (Human Visual System), an adaptive filtering decision is integrated into the deblocking process. According to three different deblocking modes appropriate for local regions with different characteristics, the perceptual and objective quality are improved without excessive smoothing the image details or insufficiently reducing the strong blocking effect on a flat region. According to the simulation results, the proposed method outperforms other deblocking algorithms in respect to PSNR (Peak Signal-to-Noise Ratio) and SSIM (Structural SIMilarity).     

Edge‐Preserving Algorithm for Block Artifact Reduction and Its Pipelined Architecture

This paper presents a new edge‐protection algorithm and its very large scale integration (VLSI) architecture for block artifact reduction. Unlike previous approaches using block classification, our algorithm utilizes pixel classification to categorize each pixel into one of two classes, namely smooth region and edge region, which are described by the edge‐protection maps. Based on these maps, a two‐step adaptive filter which includes offset filtering and edge‐preserving filtering is used to remove block artifacts. A pipelined VLSI architecture of the proposed deblocking algorithm for HD video processing is also presented in this paper. A memory‐reduced architecture for a block buffer is used to optimize memory usage. The architecture of the proposed deblocking filter is verified on FPGA Cyclone II and implemented using the ANAM 0.25 µm CMOS cell library. Our experimental results show that our proposed algorithm effectively reduces block artifacts while preserving the details. The PSNR performance of our algorithm using pixel classification is better than that of previous algorithms using block classification.     

Efficient quadtree based block-shift filtering for deblocking and deringing

The existing implementations of block-shift based filtering algorithms for deblocking are hard to achieve good smoothing performance and low computation complexity simultaneously due to their fixed block size and small shifting range. In this paper, we propose to integrate quadtree (QT) decomposition with the block-shift filtering for deblocking. By incorporating the QT decomposition, we can easily find the locations of uniform regions and determine the corresponding suitable block sizes. The variable block sizes generated by the QT decomposition facilitate the later block-shift filtering with low computational cost. In addition, large block based shift filtering can provide better deblocking results because the smoothing range of large blocks spans over the conventional 8 × 8 block size. Furthermore, we extend the proposed QT based block-shifting algorithm for deringing JPEG2000 coded images. Experimental results show the superior performance of our proposed algorithms.     

一种结合图像增强的高斯噪声组合滤波算法

为了有效滤除图像高斯噪声,将滤波算法与增强技术有机结合,提出了一种具有增强效果的组合滤波算法.该算法首先针对经典中值滤波无法有效滤除高斯噪声的缺陷,从滤波模板的角度对其加以改进,对高斯噪声进行多角度、多尺度、多级串联滤波处理,以滤除一部分噪声;然后将均值滤波引入到小波域中,对图像残余噪声实现小波域逐级均值滤波,实现对噪声的基本滤除;最后设计出一种新型小波域增强函数模型,通过设定阈值,将滤波后图像分为若干个区域,分别进行不同程度的增强处理,通过结合具体实验对不同强度下噪声与增强函数系数的取值进行定量分析,给出两者之间的函数关系式.实验证明,该滤波算法对于高强度的高斯噪声有较好的抑制效果,并且具有一定的自适应性.     

A generic post-deblocking filter for block based image compression algorithms

In this paper we propose a new post-processing deblocking technique that is independent of the compression method used to encode the image. The development of this filter was motivated by the use of Multidimensional Multiscale Parser (MMP) algorithm, a generic lossy and lossless compression method. Since it employs an adaptive block size, it presents some impairments when using the deblocking techniques presented in the literature. This led us to the development of a new and more generic deblocking method, based on total variation and adaptive bilateral filtering.The proposed method was evaluated not only for still images, but also for video sequences, encoded using pattern matching and transform based compression methods. For all cases, both the objective and subjective quality of the reconstructed images were improved, showing the versatility of the proposed technique.     

一种改进的LTE下行系统信道估计算法

基于3GPP长期演进（LTE）下行链路系统,在比较了现有几种不同信道估计算法的基础上,提出了一种适用于LTE下行系统的时频二维联合维纳迭代滤波信道估计算法。具体步骤如下：首先,采用基于奇异值分解（SVD）的线性最小均方误差（LMMSE）算法在频域进行维纳迭代滤波;然后,再利用频域估计出来的值在时域进行一次维纳迭代滤波。仿真结果表明,该算法能够有效地改善信道估计的误比特率（BER）性能,与传统的方法相比,性能更加接近于理想信道估计,同时也没有显著增加算法的运算复杂度。     

适于嵌入式系统的视频去块效应算法

为了消除基于块编码的低码率视频压缩技术中"块效应"现象,针对嵌入式多媒体处理器的结构提出了新的自适应滤波消除块效应算法.此算法在TI OMAP5910平台上实现,实验表明它有效提高客观PSNR值和改善块效应现象.同时为了满足嵌入式系统在不同应用场合下的实时处理需求,在本算法的基础上提出计算复杂度动态可调方案.     

基于滤波方法的OFDM信道估计研究

维纳滤波和卡尔曼滤波都是基于最小均方误差准则的滤波方法,本文主要研究这两种滤波方法在OFDM信道估计中的应用。为了跟踪频率选择性信道的变化,采用在OFDM系统中易于实现的梳状导频进行研究。传统的MMSE在统计意义上是最好的线性估计器,但是需要对矩阵求逆,是一种计算量较大,算法较复杂的方法。LMMSE是频域维纳滤波方法,其减小了MMSE的复杂度,但只适用于慢衰落信道,针对时变信道,本文提出卡尔曼滤波的信道估计方法,仿真结果表明,卡尔曼滤波的信道估计方法在时变信道中具有良好的性能。     

A performance optimized architecture of deblocking filter for H.264/AVC

The in-loop deblocking filter is one of the complex parts in H.264/AVC. It has such a large amount of computation that almost all the pixels in all the frames are involved in the worst case. In this paper, a fast deblocking filter architecture is proposed, and it can effectively save the operating time. In the proposed architecture, two 1-D filters are introduced so that the vertical filtering and the horizontal filtering can be performed at the same time, Only 120 cycles are needed for a macroblock. Our architecture is also a memory efficient one, and only one 4×4 pixels register, one 4×4 transpose array and one 16×32 b two-port (SRAM) are used as buffers in the filtering process. The simulation and synthesis results show that, with almost the same or even smaller area than some 1-D filter based architectures before, the proposed one can save more than 40% processing time. The architecture is suitable for real-time applications and can easily achieve the requirement of processing real-time video in 1080HD (high definition format, 1 920×1 088@30 fps) at 100 MHz.