A parallel algorithm for color constancy

Objects retain their color in spite of changes in the wavelength and energy composition of the light they reflect. This phenomenon is called color constancy and plays an important role in computer vision research. We have devised a parallel algorithm for color constancy. The algorithm runs on a two-dimensional grid of processors each of which can exchange information with its four neighboring processors. Each processor calculates local average color. This information is then used to estimate the reflectances of the object. The algorithm was tested on several images of everyday objects. The algorithm also works for scenes where the illuminant changes smoothly over the image.     

一种新的基于颜色恒常性的肤色分割算法

为了解决不同光照条件下的肤色分割问题,提出了一种新颖并且行之有效的解决方法。该方法先应用颜色恒常性算法对图像光照进行估计,根据光照估计的结果,在YCbCr颜色空间采用不同分布的高斯肤色模型,并利用动态阈值对图像进行分割。试验结果证明了算法的可行性和优越性。     

Automatic color constancy algorithm selection and combination

In this work, we investigate how illuminant estimation techniques can be improved taking into account intrinsic, low level properties of the images. We show how these properties can be used to drive, given a set of illuminant estimation algorithms, the selection of the best algorithm for a given image. The algorithm selection is made by a decision forest composed of several trees on the basis of the values of a set of heterogeneous features. The features represent the image content in terms of low-level visual properties. The trees are trained to select the algorithm that minimizes the expected error in illuminant estimation. We also designed a combination strategy that estimates the illuminant as a weighted sum of the different algorithms’ estimations. Experimental results on the widely used Ciurea and Funt dataset demonstrate the effectiveness of our approach.     

A real-time neural system for color constancy

A neural network approach to the problem of color constancy is presented. Various algorithms based on Land's retinex theory are discussed with respect to neurobiological parallels, computational efficiency, and suitability for VLSI implementation. The efficiency of one algorithm is improved by the application of resistive grids and is tested in computer simulations; the simulations make clear the strengths and weaknesses of the algorithm. A novel extension to the algorithm is developed to address its weaknesses. An electronic system that is based on the original algorithm and that operates at video rates was built using subthreshold analog CMOS VLSI resistive grids. The system displays color constancy abilities and qualitatively mimics aspects of human color perception.     

A multistage neural network for color constancy and color induction

A biologically-based multistage neural network is presented which produces color constant responses to a variety of color stimuli. The network takes advantage of several mechanisms in the human visual system, including retinal adaptation, spectral opponency, and spectrally-specific long-range inhibition. This last stage is a novel mechanism based on cells which have been described in cortical area V4. All stages include nonlinear response functions. The model emulates human performance in several psychophysical paradigms designed to test color constancy and color induction. We measured the amount of constancy achieved with both natural and artificial simulated illuminants, using homogeneous grey backgrounds and more complex backgrounds, such as Mondrians. On average, the model performs as well or better than the average human color constancy performance under similar conditions. The network simulation also displays color induction and assimilation behavior consistent with human perceptual data.     

一种新型的快速色彩平衡算法

在图像处理中,为了提高传统色彩平衡算法的计算速度、降低算法的复杂度,提出了一种全新的快速色彩平衡算法,即过滤少量极端像素颜色值并按比例提高剩余的非极端像素颜色值的方法.通过对多幅图片的处理,相对于传统的色彩平衡方法,该算法得到了更好的效果、具有更好的性能.     

一种新的多传感器彩色图像融合方法

针对多传感器彩色图像的融合问题,提出了一种基于高斯同态滤波和YIQ变换的融合方法.对源图像进行YIQ变换,并设计一种动态高斯同态滤波器,在频域内处理各图像的亮度分量,在保持图像彩色信息的同时增强图像细节.运用不同的小波变换规则,对亮度分量和色度分量分别进行融合.将各分量的融合结果逆变换至RGB空间,得到融合图像.实验分析表明:新算法得到的融合图像无论在视觉效果还是在客观评价方面,均优于小波变换方法和Laplace塔型方法,具有令人满意的融合效果.     

Multi-objective optimization based color constancy

This paper presents a new combining approach for color constancy, the problem of finding the true color of objects independent of the light illuminating the scene. There are various combining methods in the literature that all of them use weighting approach with either pre-determined static weights for all images or dynamically computed weights for each image. The problem with weighting approach is that due to the inherent characteristics of color constancy methods, finding suitable weights for combination is a difficult and error-prone task. In this paper, a new optimization based combining method is proposed which does not need explicit weight assignment. The proposed method has two phases: first, the best group of color constancy algorithms for the given image is determined and then, some of the algorithms in this group are combined using multi-objective optimization methods. To the best of our knowledge, this is the first time that optimization methods are used in color constancy problem. The proposed method has been evaluated using two benchmark datasets and the experimental results were satisfactory in compare with state of the art algorithms.     

基于视锥细胞色适应生理机制的颜色恒常性计算

通过模拟人类底层视觉系统中的颜色恒常处理机制,提出基于视锥细胞色适应生理机制的颜色恒常性计算方法,利用视锥细胞的色适应计算代替基于灰度边缘假设的颜色恒常性计算方法所采用的Von Kries对角变换.实验结果及定量定性的分析表明本文方法比原计算模型下的算法颜色校正效果要好,能有效恢复图像中物体的本质颜色,且性能更稳定.从计算神经科学的角度,本文方法支持视锥细胞的色适应生理机制在视觉颜色恒常性中扮演重要角色的观点.     

A sequential Bayesian approach to color constancy using non-uniform filters

This paper introduces a non-uniform filter formulation into the Brainard and Freeman Bayesian color constancy technique. The formulation comprises sensor measurements taken through a non-uniform filter, of spatially-varying spectral sensitivity, placed on the camera lens. The main goal of this paper is twofold. First, it presents a framework in which sensor measurements obtained through a non-uniform filter can be sequentially incorporated into the Bayesian probabilistic formulation. Second, it shows that such additional measurements obtained reduce the effect of the prior in Bayesian color constancy. For the purposes of testing the proposed framework, we use a filter formulation of two portions of different spectral sensitivities. We show through experiments on real data that improvement in the parameter estimation can be obtained inexpensively by sequentially incorporating additional information obtained from the sensor through the different portions of a filter by Bayesian chaining. We also show that our approach outperforms previous approaches in the literature.     

Computational color constancy from maximal projections mean assumption

In this paper, we propose an efficient algorithm for illuminant estimation. The 2D estimator is derived based on the maximal projections’ mean assumption according to which the estimated illuminant in a chromaticity subspace is the vector maximizing the sum of orthogonal projections of image colors. We show that, the illuminant estimation solution is the eigenvector corresponding to the maximal eigenvalue of the inner-product matrix of data. The 2D estimator is extended to the 3D space by minimizing the reconstruction errors from the 2D estimates obtained in the RGB color space. The evaluation of the 3D resulting estimator on three well-known image datasets generates lower estimation errors.     

一种用于色彩量化的调色板快速搜索算法

为加快色彩量化中色彩映像过程的计算速度,提出了一种等范数等加和调色板搜索算法ENESPS。该算法选择与待映射像素色彩矢量的范数最接近的调色板色彩作为初始搜索点,然后利用范数限定条件和加和限定条件来缩小调色板搜索范围。实验结果表明,相对于其他一些搜索方法,ENESPS能有效缩短平均搜索长度,并明显减少色彩量化所需的计算时间。     

A fuzzy algorithm for color quantization of images

In this paper, we review a number of techniques for fuzzy color quantization. We show that the fuzzy membership paradigm is particularly suited to color quantization, where color cluster boundaries are not well defined. We propose a new fuzzy color quantization technique which incorporates a term for partition index. This algorithm produces better results than fuzzy C-means at a reduced computational cost. We test the results of the fuzzy algorithms using quality metrics which model the perception of the human visual system and illustrate that substantial quality improvements are achieved.     

一种快速颜色传输算法

图像间的颜色传输是将一幅图像的颜色特征传输给另一幅图像,使目标图像具有与参考图像相似的色彩。提出一种自动的、快速颜色传输算法。在HSV空间模糊聚类生成代表不同色调特征的样本区域;通过计算各样本区域的特征向量间的距离,建立样本区域之间的匹配关系;利用图像在ιαβ 空间的基本统计信息进行局部颜色传输;最后利用隶属度因子融合局部传输效果。对有效色调值进行加权聚类,大大降低聚类样本数量,在取得较好的颜色传输效果的同时,显著地提高了传输速度。     

彩色地图分色算法研究现状

对已有彩色地图分色方法进行了综述.把彩色地图分色方法细分成颜色空间的选择和具体的分割方法两个方面,并从上述两个方面进行了总结.具体分割算法包括基于直方图的阈值化方法,基于特征空间的聚类、基于模糊的方法、基于神经网络的方法、基于熵的方法、基于遗传算法的方法、基于随机场模型的统计学方法以及其它一些方法.颜色空间模型包括RGB颜色空间、CIELab空间、HVC空间、HLS颜色空间等.     

一种新的指纹图像分割算法

指纹图像分割是自动指纹识别的重要步骤。对指纹特征和传统指纹分割方法进行了研究,提出了一种新的指纹图像分割算法。先对指纹图像进行裁剪,如果指纹图像对比度较低,则对图像进行均衡化处理;然后对图像进行顶帽变换,补偿不均匀的背景亮度;最后用迭代自组织分析算法(ISODATA聚类)对图像进行分块分割和形态学图像处理。对国际指纹识别竞赛(FVC)数据库不同质量的指纹进行了测试,实验结果表明,此算法对不同质量的指纹是有效的,效果好于传统指纹分割方法。     

A novel color image encryption algorithm based on DNA sequence operation and hyper-chaotic system

A new color image encryption algorithm based on DNA (Deoxyribonucleic acid) sequence addition operation is presented. Firstly, three DNA sequence matrices are obtained by encoding the original color image which can be converted into three matrices R, G and B. Secondly, we use the chaotic sequences generated by Chen's hyper-chaotic maps to scramble the locations of elements from three DNA sequence matrices, and then divide three DNA sequence matrices into some equal blocks respectively. Thirdly, we add these blocks by using DNA sequence addition operation and Chen's hyper-chaotic maps. At last, by decoding the DNA sequence matrices and recombining the three channels R, G and B, we get the encrypted color image. The simulation results and security analysis show that our algorithm not only has good encryption effect, but also has the ability of resisting exhaustive attack, statistical attack and differential attack.     

空域彩色图像的二级置乱算法

以图像信息安全问题为背景,针对彩色图像的存储特性,给出了一种空域彩色图像的二级置乱算法.其利用改进的Gray码技术对彩色图像的三基色进行置乱,借助彩色图像的自身信息构造置乱索引矩阵,对彩色图像的位置信息进行遍历变换.此方法即安全又方便.实验结果表明,与其它方法相比,该算法有良好的置乱度,且易于实现,同时提高了加密效率.