基于改进主动表观模型算法的人脸特征定位

人脸特征点的精确定位一直是人脸图像处理的重要研究内容,特征点定位精确与否直接影响后续工作结果的好坏。在基于反向组合AAM（Active Appearance Models）人脸特征点定位算法的基础上,提出结合特征点局部纹理模型来对AAM初始形状参数做最优化以及对AAM匹配模板升级的改进。改进的算法采用特征点局部纹理模型和AAM全局纹理模型结合的方法来最优化AAM初始形状参数,并在此前提下对AAM匹配模板进行升级,使其更接近待匹配图像的信息。在精确的匹配模板和优化的初始形状参数下,匹配的最终精度会得到提升。实验和理论证明,改进后的算法比传统反向组合AAM算法以及现有改进的PAAM（Progressive AAM）算法以及简单的结合ASM和AAM的改进算法都有更好的特征点定位精度。     

基于AAM的人脸图像描述与编码

利用主动表观模型(AAM)来对人脸图像进行描述和编码,经过一定次数迭代,进行模型和人脸匹配,合成人脸图像.方法基于统计信息建模来实现对目标图像的描述.由于采用了优化算法,经过迭代运算使合成的模型与目标图像不断接近,最终能得到反应目标图像纹理及形状的合成模型.实验表明AAM方法进行人脸描述和编码的有效性.方法在人脸图像编码有重要的意义.     

USAN-AAM人脸特征点快速定位方法*

基于反向合成算法的AAM（active appearance model）是一种快速而高效的人脸特征点定位方法,但由于其纹理模型仅包含灰度信息,当测试数据集中的图像光线条件和训练数据集中的图像光线条件有较大差异时,算法定位精度明显下降。基于此,提出了一种改进的AAM人脸特征点定位方法USAN-AAM。实验结果表明,与原方法相比,该方法对光线变化更鲁棒,定位精度也更高。     

噪声对基于不同梯度算子的ICG算法的影响

反向合成梯度算法是一种基于局部指向性的反向合成图像对齐算法,能有效克服光照变化对匹配结果准确性的影响。局部指向性的计算在本质上是梯度的计算,可以用不同的梯度算子求解。该文采用4种梯度算子计算局部指向性,通过给输入图像和模板图像中加入噪声模拟实际图像,研究了噪声对基于4种梯度算子的反向合成梯度算法的影响。     

梯度算子对反向合成梯度算法的影响

反向合成梯度算法是一种基于局部指向性的反向合成图像对齐算法。与传统的反向合成图像对齐算法相比,该算法可有效地克服光照变化对匹配结果的影响[1]。由于局部指向性的计算在本质上是梯度的计算,而图像梯度的计算可以采用不同的梯度算子,因此采用4种不同的梯度算子（一阶差分算子,Roberts算子,Sobel算子和Prewitt算子）来计算局部指向性,并通过实验比较分析了4种梯度算子对反向合成梯度算法的影响。     

基于AAM姿态校正的人脸识别

非约束环境下,光照、姿态、表情、遮挡、复杂背景等因素给人脸识别带来严重影响。主动表观模型(Active Appearance Model, AAM) 能够建立包含人脸形状和纹理信息的先验模型对图像中的人脸进行匹配,合成新的人脸图像。Gabor特征被广泛地应用在人脸识别中,并取得了很好的效果。利用AAM对人脸图像进行姿态校正,合成标准正面人脸图像,然后提取图像的熵增强Gabor jets特征,使用带有阈值的Borda count分类器进行人脸识别。在IMM数据库上的试验表明,改进的方法对姿态、表情以及遮挡具有更高的鲁棒性,可以得到更好的识别效果。     

基于局部指向性的反向合成图像对齐算法

传统的反向合成图像对齐算法比较的是模板图像与输入图像之间的像素值。该方法容易受到图像中光照变化的影响，从而导致收敛性变差甚至发散。根据局部指向性对光照变化不敏感的特性，提出了一种新的反向合成图像对齐算法——反向合成梯度算法。由于局部指向性的计算在本质上是图像梯度的计算，因此采用几种不同的梯度算子来计算局部指向性。通过实验，验证了反向合成梯度算法能够有效克服图像中光照变化的影响，同时比较了不同算子在不同光照下对反向合成梯度算法的影响。     

基于主动表观模型姿态矫正和局部加权匹配人脸识别

非约束环境下,光照、姿态、表情、遮挡等复杂背景因素给人脸识别带来严重影响。提出一种基于AAM（active appearance model）的图像对齐和局部匹配人脸识别算法,使之能够增强人脸识别算法对姿态、表情变化的鲁棒性。AAM能够快速准确地定位人脸的特征点,进而将图像扭转到一个标准正面人脸模型中。接着,提出一种新的基于信息熵的Gabor jet加权方法用于提高人脸识别率;并且对Borda count分类器组合方法进行了改进,认为在投票过程中为其设置阈值来排除“噪声”的干扰可以提高识别率。通过与多种人脸识别方法的实验结果比较表明,使用AAM矫正图像后,联合熵加权Gabor方法和加阈值Borda能够取得比单独使用更好的成绩。     

基于反向映射的图像间颜色迁移算法仿真

现有的图像间颜色迁移算法普遍存在颜色误迁率高的问题,为此在传统颜色迁移算法的基础上,引入反向映射对颜色迁移算法进行优化。首先通过对图像的特征提取,获得目标图像的主色,对提取结果做平滑处理。通过色彩空间转换和色调反向映射两个步骤,实现图像的形态学变换,得到过渡图像。在过渡图像上做K均值聚类匹配操作,并通过分层迁移和全局迁移两种方式,得到颜色迁移的最优化能量方程。将反向映射颜色迁移算法与传统算法放入仿真环境当中,进行仿真对比实验,通过实验发现传统方法的平均误迁率为12.3%,而反向映射颜色迁移算法的误迁率仅为0.27%。     

非约束环境下人脸特征点的稳定跟踪

为了对人脸特征点进行精确地跟踪,提出一种在线参考表观模型(ORAM)的算法.首先在原主动表观模型(AAM)中加入在线更新的参考模型;然后采用子空间在线自更新机制,利用增量学习方法在线更新AAM的纹理模型和参考模型;在此基础上,基于同步反向合成建立ORAM的特征点拟合算法.为减少跟踪过程产生的累积误差,利用初始稳定跟踪结果建立纹理子空间重置机制,完成人脸特征点跟踪.实验结果表明,ORAM算法无需训练集,在姿态、表情、光照变化的环境下,能够准确、快速地完成人脸跟踪.     

基于MR-AAM双重拟合的人脸特征点定位方法

传统的主动表观模型(AAM)反向组合算法仅进行了单次拟合过程,当初始位置与目标对象偏移过大时,往往会陷入局部最小,难以收敛到正确位置。针对此问题,提出了一种基于多分辨率AAM(MR-AAM)的双重拟合方法,首先在低分辨率模型下进行第一次拟合以确定面部初始位置,然后在高分辨率模型下进行二次拟合。由于能够快速获得较准确的初始位置,进而取得较好的人脸特征标定结果。实验结果表明,所提方法与传统方法相比,在能保证实时的情况下,提高了拟合精度。     

Groupwise geometric and photometric direct image registration

Image registration consists in estimating geometric and photometric transformations that align two images as best as possible. The direct approach consists in minimizing the discrepancy in the intensity or color of the pixels. The inverse compositional algorithm has been recently proposed by Baker et al. for the direct estimation of groupwise geometric transformations. It is efficient in that it performs several computationally expensive calculations at a pre-computation phase. Photometric transformations act on the value of the pixels. They account for effects such as lighting change. Jointly estimating geometric and photometric transformations is thus important for many tasks such as image mosaicing. We propose an algorithm to jointly estimate groupwise geometric and photometric transformations while preserving the efficient pre-computation based design of the original inverse compositional algorithm. It is called the dual inverse compositional algorithm. It uses different approximations than the simultaneous inverse compositional algorithm and handles groupwise geometric and global photometric transformations. Its name stems from the fact that it uses an inverse compositional update rule for both the geometric and the photometric transformations. We demonstrate the proposed algorithm and compare it to previous ones on simulated and real data. This shows clear improvements in computational efficiency and in terms of convergence.     

采用多尺度掩模消除干扰的反向组合算法

反向组合算法是最有效的图像对齐算法之一,但该算法抗干扰能力差.当输入图像部分被遮挡时,图像对齐效果变差.针对该问题,我们提出一种采用多尺度掩模消除干扰的反向组合算法.该算法采用自适应的方法设置初始掩模,再通过迭代判断和逐层分块来细化初始掩模,使得掩模能准确地设置在干扰区域上.实验结果表明,该算法既保留了原反向组合算法的优点,又提高了算法抗干扰的能力,使得反向组合算法能在更复杂的环境下进行图像对齐.     

Active Appearance Models Revisited

Active Appearance Models (AAMs) and the closely related concepts of Morphable Models and Active Blobs are generative models of a certain visual phenomenon. Although linear in both shape and appearance, overall, AAMs are nonlinear parametric models in terms of the pixel intensities. Fitting an AAM to an image consists of minimising the error between the input image and the closest model instance; i.e. solving a nonlinear optimisation problem. We propose an efficient fitting algorithm for AAMs based on the inverse compositional image alignment algorithm. We show that the effects of appearance variation during fitting can be precomputed (projected out) using this algorithm and how it can be extended to include a global shape normalising warp, typically a 2D similarity transformation. We evaluate our algorithm to determine which of its novel aspects improve AAM fitting performance.Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/B:VISI.0000029666.37597.d3     

A Unified Gradient-Based Approach for Combining ASM into AAM

Active Appearance Model (AAM) framework is a very useful method that can fit the shape and appearance model to the input image for various image analysis and synthesis problems. However, since the goal of the AAM fitting algorithm is to minimize the residual error between the model appearance and the input image, it often fails to accurately converge to the landmark points of the input image. To alleviate this weakness, we have combined Active Shape Models (ASM) into AAMs, in which ASMs try to find correct landmark points using the local profile model. Since the original objective function of the ASM search is not appropriate for combining these methods, we derive a gradient based iterative method by modifying the objective function of the ASM search. Then, we propose a new fitting method that combines the objective functions of both ASM and AAM into a single objective function in a gradient based optimization framework. Experimental results show that the proposed fitting method reduces the average fitting error when compared with existing fitting methods such as ASM, AAM, and Texture Constrained-ASM (TC-ASM) and improves the performance of facial expression recognition significantly.     

一种基于偏转角度的AAM人脸特征点定位方法

对有偏转角度的人脸特征点定位来说,拟合初始位置和模型的角度对人脸特征点定位效果有很大的影响。而传统的AAM（Active Appearance Models）人脸特征定位方法没有具体考虑这一问题,对有偏转角度的人脸特征点的定位准确率和速度并不理想。为解决这个问题,文中提出了一种利用两眼中心坐标和嘴中心坐标来计算人脸偏转角度,根据坐标和角度确定拟合初始位置和模板的方法。用Adaboost和YCbCr对人脸进行预检测,根据找到的特征区域计算偏转角,用反向算法结合该角度的模板进行特征点定位。实验的测试结果表明本方法对有偏转角度的人脸的特征点定位比传统方法在准确度和速度上都有了提高。     

一种鲁棒高效的人脸特征点跟踪方法

人脸特征点跟踪能获取除粗略的人脸位置和运动轨迹以外的人脸部件的精确信息,对计算机视觉研究有重要作用.主动表象模型(Active appearance model, AAM)是描述人脸特征点位置的最有效的方法之一,但是其高维参数空间和梯度下降优化策略使得AAM对初始参数敏感,且易陷入局部极值. 因此,基于传统AAM的人脸特征点跟踪方法不能同时较好地解决大姿态、光照和表情的问题.本文在多视角AAM的框架下,提出一种结合随机森林和线性判别分析(Linear discriminate analysis, LDA)的实时姿态估计算法对跟踪的人脸进行姿态预估计和更新,从而有效地解决了视频人脸大姿态变化的问题.提出了一种改进的在线表象模型(Online appearance model, OAM)方法来评估跟踪的准确性,并自适应地通过增量主成分分析(Principle component analysis, PCA) 学习来更新AAM的纹理模型,极大地提高了跟踪的稳定性和模型应对光照和表情变化的能力.实验结果表明,本文算法在视频人脸特征点跟踪的准确性、鲁棒性和实时性方面都有良好的性能.     

Multi-View AAM Fitting and Construction

Active Appearance Models (AAMs) are generative, parametric models that have been successfully used in the past to model deformable objects such as human faces. The original AAMs formulation was 2D, but they have recently been extended to include a 3D shape model. A variety of single-view algorithms exist for fitting and constructing 3D AAMs but one area that has not been studied is multi-view algorithms. In this paper we present multi-view algorithms for both fitting and constructing 3D AAMs. Fitting an AAM to an image consists of minimizing the error between the input image and the closest model instance; i.e. solving a nonlinear optimization problem. In the first part of the paper we describe an algorithm for fitting a single AAM to multiple images, captured simultaneously by cameras with arbitrary locations, rotations, and response functions. This algorithm uses the scaled orthographic imaging model used by previous authors, and in the process of fitting computes, or calibrates, the scaled orthographic camera matrices. In the second part of the paper we describe an extension of this algorithm to calibrate weak perspective (or full perspective) camera models for each of the cameras. In essence, we use the human face as a (non-rigid) calibration grid. We demonstrate that the performance of this algorithm is roughly comparable to a standard algorithm using a calibration grid. In the third part of the paper, we show how camera calibration improves the performance of AAM fitting. A variety of non-rigid structure-from-motion algorithms, both single-view and multi-view, have been proposed that can be used to construct the corresponding 3D non-rigid shape models of a 2D AAM. In the final part of the paper, we show that constructing a 3D face model using non-rigid structure-from-motion suffers from the Bas-Relief ambiguity and may result in a “scaled” (stretched/compressed) model. We outline a robust non-rigid motion-stereo algorithm for calibrated multi-view 3D AAM construction and show how using calibrated multi-view motion-stereo can eliminate the Bas-Relief ambiguity and yield face models with higher 3D fidelity. Electronic Supplementary Material The online version of this article () contains supplementary material, which is available to authorized users.     

A background robust active appearance model using active contour technique

This paper proposes an active contour-based active appearance model (AAM) that is robust to a cluttered background and a large motion. The proposed AAM fitting algorithm consists of two alternating procedures: active contour fitting to find the contour sample that best fits the face image and then the active appearance model fitting over the best selected contour. We also suggest an effective fitness function for fitting the contour samples to the face boundary in the active contour technique; this function defines the quality of fitness in terms of the strength and/or the length of edge features. Experimental results show that the proposed active contour-based AAM provides better accuracy and convergence characteristics in terms of RMS error and convergence rate than the existing robust AAM. The combination of the existing robust AAM and the proposed active contour-based AAM (AC-R-AAM) had the best accuracy and convergence performances.