影像纹理分类的马尔可夫随机场方法与试验研究

针对马尔可夫随机场方法用于影像纹理分类进行了探讨。主要探讨了以下三个方面的问题：（１）如何从备选马尔可夫随机场模型中找出最适合的模型;（２）马尔可夫随机场模型参数的估计问题;（３）如何利用马尔可夫随机场模型参数进行影像纹理分类。最后以实际试验情况表明所提出的方法是可行的。     

一种基于DA-STMRF模型的运动目标分割方法

为克服传统的时空马尔可夫随机场模型中全局一致平滑约束引起的过平滑,根据间断自适应的思想,结合边缘信息,提出了一种基于间断自适应时空马尔可夫随机场模型的运动目标分割方法。帧差图像二值化得到初始标记场,初始标记场进行“与”操作获得共同标记场,通过构造相应的能量函数,用Metroplis采样器算法实现共同标记场的优化。通过实验验证了该算法的有效性。     

对马尔可夫随机场特征级图像融合的改进

提出了一种基于MAP的Markov随机场的图像融合方法。将感兴趣区特征的均值与方差作为马尔可夫随机场的概率参数,选取合适的模型,根据优化算法快速求得MAP解,完成图像初始标记过程,根据最大后验概率模型,对图像进行特征层融合。通过两组遥感图像的实验,证明MAP-MRF模型在遥感图像特征层融合中,具有较目前常用方法更好的效果。     

基于马尔可夫随机场的运动分割研究

运动对象的分割技术一直是图像处理和计算机视觉领域的重要研究课题。采用一种将运动估计方法与马尔可夫随机场（MRF）模型相结合的运动分割方法。采用鲁棒统计技术与误差模型相结合构成运动估计的目标函数,运动模型为仿射运动,通过过松弛算法获得每种运动的运动参数;根据误差最小原则确定运动对应区域的初值,采用马尔可夫随机场（MRF）模型对运动估计结果进行平滑去噪。最后给出了该方法在通用图像实例上的实验结果。     

高斯均值场变分推理的收敛性和精确性

高斯马尔可夫随机场模型是具有马尔可夫性质、符合多元高斯分布的概率模型.均值场变分方法是图模型最基本的变分近似推理方法.基于指数族变分近似推理框架,分析了高斯马尔可夫随机场模型均值场变分近似推理的收敛性和精确性,证明了均值场变分近似推理关于一阶均值参数是收敛的.进一步给出了模型的各个变量不完全独立时,对数配分函数的最优下界和迭代误差的解析式.最后,通过数值模拟实验,验证了理论分析的结果.     

一种无接缝纹理映射算法

针对基于图像三维重构得到的三维形状的纹理映射算法通常存在接缝现象的问题,提出一种无接缝纹理映射算法。该算法通过建立三维网格顶点和视点之间的马尔可夫随机场模型,利用重心坐标权重插值进行颜色填充,构造出一个无接缝的纹理图像。实验结果表明,马尔可夫随机场模型可以在保证纹理图像质量的同时最小化接缝现象,在此基础上的权重颜色插值方法能够完全消除接缝现象。     

基于混合高斯模型MRF场的CT图像分割

提出了一种基于混合高斯模型的马尔可夫随机场CT图像分割方法.此方法根据工业CT图像的特点,建立混合高斯逼近的图像灰度统计模型;用混合高斯模型作为Markov随机场的先验模型,提出混合高斯Markov随机场分割模型.实验表明,该方法较单高斯模型有很大的改善,对工业CT图像分割效果好.     

面向智能视频监控中的运动目标检测方法研究

运动目标检测是实现智能视频监控的基础,针对当前运动目标检测方法在复杂场景中适应性差的问题,提出了一种结合时空马尔可夫随机场模型和高斯混合模型的运动目标检测方法。在训练时空马尔可夫随机场模型时,采用高斯混合模型的参数更新算法计算邻域图像分割区域的均值和方差,并通过时空邻域标记场设置势函数。通过与传统目标检测方法的仿真比较,验证了该方法的优越性。结果表明,与传统的目标检测方法相比,该方法在复杂场景下具有更高的检测精度,能够更清晰地分割前景中的运动目标。     

基于马尔可夫模型优化的非经典感受野轮廓检测算法

基于非经典感受野的同性抑制作用提出一种新的算法。该算法首先将多级周边抑制引入到各项同性检测模型中;其次根据集合理论,结合边缘生长过程控制思想提出一种改进的组合方法,解决了抑制参数取值对轮廓检测的影响;最后根据马尔可夫随机场理论建立轮廓概率模型,得到最终优化后的输出轮廓。实验结果分析表明,新算法精度高,明显优于传统方法。     

图像分割中的马尔可夫随机场方法综述

马尔可夫随机场方法是图像分割中一个极为活跃的研究方向。本文介绍了基于马尔可夫随机场模型的一般理论与图像的关系,给出它在图像分割中的通用框架:包括空域和小波域图像模型的建立、最优准则的选取、标号数的确定、图像模型参数的估计和图像分割的实现,评述了其在图像分割中的应用,展望其发展的方向。     

Fields of Experts

We develop a framework for learning generic, expressive image priors that capture the statistics of natural scenes and can be used for a variety of machine vision tasks. The approach provides a practical method for learning high-order Markov random field (MRF) models with potential functions that extend over large pixel neighborhoods. These clique potentials are modeled using the Product-of-Experts framework that uses non-linear functions of many linear filter responses. In contrast to previous MRF approaches all parameters, including the linear filters themselves, are learned from training data. We demonstrate the capabilities of this Field-of-Experts model with two example applications, image denoising and image inpainting, which are implemented using a simple, approximate inference scheme. While the model is trained on a generic image database and is not tuned toward a specific application, we obtain results that compete with specialized techniques. The work for this paper was performed while S.R. was at Brown University.     

Normalized filter pool for prior modeling of nature images

Markov random field (MRF), as one of special undirected graphs, is widely used in modeling priors of natural images. Targeting to learn better prior models from a given database, we explore the natural image statistics at different scales and build normalized filter pool, a kind of high-order MRF, for prior learning of nature images. The main contribution of the proposed model is that we construct a multi-scale MRF model through constraining the norms of filters in kernel space and integrate all the filtering responses in a unified framework. We formulate both learning and inference as constrained optimization problems and solve them using augmented Lagrange method. The experiment results demonstrate that the normalization of filters at different scales helps to achieve fast convergence in learning stage and obtain superior performance in image restoration, e.g., image denoising and image inpainting.     

深度卷积神经网络降噪模型的技术瓶颈与研究展望

现有的深度卷积神经网络（DCNN）图像降噪模型受其技术路线内在固有特性的制约,降噪性能仍然有待进一步改进。为了推动现有DCNN图像降噪模型技术的发展,需要正视并及时解决制约其进一步完善的瓶颈问题。本文简要概述了传统的基于自然图像非局部自相似性、稀疏性和低秩性这3种先验知识设计的图像降噪算法的技术路线特点和优缺点,从传统图像降噪算法存在的问题中引出基于DCNN构建图像降噪模型的技术优势,并梳理并总结了DCNN降噪模型未来的发展瓶颈,就相应的解决方案（研究方向）进行详细讨论。通过深入分析发现,可以从扩大卷积核的感受野、降低网络参数与训练集之间的依赖关系以及充分利用DCNN网络的建模能力这3个角度入手,突破现有基于数据驱动的DCNN降噪模型的瓶颈制约,把图像降噪算法的研究水平推向新的高度。     

基于模糊分类的MRF图像恢复方法

运用马尔科夫随机场(MRF)进行图像处理时,对图像平滑区域与边缘区域所采用的处理方法不加区别,会导致大量冗余程序且运行时间过长。针对该问题,提出基于模糊分类的MRF图像恢复方法,根据图像子块内服从不同分布的像素统计特征,对图像子块进行模糊分类,在分类基础上应用MRF进行图像恢复。对退化的二值图像进行恢复实验,结果表明,与MRF方法相比,基于模糊分类的MRF方法能减少程序运行时间,改善去噪效果。     

梯度双边滤波的图像去噪

为了改善双边滤波的去噪性能,引入图像的局部模式,提出了梯度双边滤波算法。采用相邻像素亮度值的梯度距离来构造梯度相似度核,通过几何邻近度核函数和梯度相似度核函数来对图像邻域像素进行加权平均,从而实现滤波;为了获得最佳的滤波参数,通过经验学习的方法对滤波参数进行选择,最终得到通用的参数配置。实验结果表明,新方法能很好地保持图像的边缘,且与传统去噪模型相比,其去噪性能也是最好的。     

Scale selection for anisotropic diffusion filter by Markov random field model

The selection of stopping time (i.e., scale) significantly affects the performance of anisotropic diffusion filter for image denoising. This paper designs a Markov random field (MRF) scale selection model, which selects scales for image segments, then the denoised image is the composition of segments at their optimal scales in the scale space. Firstly, statistics-based scale selection criteria are proposed for image segments. Then we design a scale selection energy function in the MRF framework by considering the scale coherence between neighboring segments. A segment-based noise estimation algorithm is also developed to estimate the noise statistics efficiently. Experiments show that the performance of MRF scale selection model is much better than the previous global scale selection schemes. Combined with this scale selection model, the anisotropic diffusion filter is comparable to or even outperform the state-of-the-art denoising methods in performance.     

基于双树复小波二元统计模型的图像去噪方法

为了更有效地进行图像去噪,提出了一种基于双树复小波二元统计模型的图像去噪方法,该方法先用带参数的二元广义高斯分布(GGD)来模拟原图双树复小波系数的统计分布;然后结合最大似然估计(MLE)得到优化的参数估计;最后在此先验分布的基础上,运用最大后验概率(MAP)来估计从噪声图的小波系数中恢复原图的系数,从而达到去噪的目的。实验表明该新方法不仅可以干净地去除图像的噪声,还可以有效地保留图像细节,取得了良好的去噪效果,尤其是去噪图像的视觉效果要明显优于目前的很多算法。     

The use of Markov Random Fields as models of texture

We propose Markov Random Fields (MRFs) as probabilistic models of digital image texture where a textured region is viewed as a finite sample of a two-dimensional random process describable by its statistical parameters. MRFs are multidimensional generalizations of Markov chains defined in terms of conditional probabilities associated with spatial neighborhoods. We present an algorithm that generates an MRF on a finite toroidal square lattice from an independent identically distributed (i.i.d.) array of random variables and a given set of independent real-valued statistical parameters. The parametric specification of a consistent collection of MRF conditional probabilities is a general result known as the MRF-Gibbs Random Field (GRF) equivalence. The MRF statistical parameters control the size and directionality of the clusters of adjacent similar pixels which are basic to texture discrimination and thus seem to constitute an efficient model of texture. In the last part of this paper we outline an MRF parameter estimation method and goodness of fit statistical tests applicable to MRF models for a given unknown digital image texture on a finite toroidal square lattice. The estimated parameters may be used as basic features in texture classification. Alternatively these parameters may be used in conjunction with the MRF generation algorithm as a powerful data compression scheme.     

Modeling textured images using generalized long correlation models

The long correlation (LC) models are a general class of random field (RF) models which are able to model correlations, extending over large image regions with few model parameters. The LC models have seen limited use, due to lack of an effective method for estimating the model parameters. In this work, we develop an estimation scheme for a very general form of this model and demonstrate its applicability to texture modeling applications. The relationship of the generalized LC models to other classes of RF models, namely the simultaneous autoregressive (SAR) and Markov random field (MRF) models, is shown. While it is known that the SAR model is a special case of the LC model, we show that the MRF model is also encompassed by this model. Consequently, the LC model may be considered as a generalization of the SAR and MRF models     

结合PCA及字典学习的高光谱图像自适应去噪方法

高光谱图像各波段图像噪声分布复杂,传统去噪方法难以达到理想效果。针对这一问题,在主成分分析（PCA）的基础上,结合噪声估计和字典学习,提出一种新的高光谱去噪方法。首先,对原始高光谱数据进行主成分变换得到一组主成分图像并根据能量比重将其划分为清晰图像组和含噪图像组;然后,根据任一波段图像的信息,利用奇异值分解（SVD）对图像进行噪声估计,再将得到的噪声估计方法与K-SVD字典学习去噪算法结合,提出一种具备自适应噪声估计特性的字典学习去噪算法,并将其应用于信息量较小的含噪图像组进行去噪处理;最后,按各主成分图像对应的信息量比例进行加权融合得到最终的去噪图像。通过对模拟与实际高光谱遥感图像的实验表明,与PCA、PCA-Bish、PCA-Contourlet三种去噪方法相比,所提方法去噪后图像的峰值信噪比（PSNR）可以提升1~3 dB,且具有更多的细节信息和更好的视觉效果。