Stevens's brightness law, contrast gain control, and edge integration in achromatic color perception: a unified model

The brightness of an isolated test patch is related to its luminance by a power law having an exponent of about 1/3, a result known as Stevens's brightness law. The brightness law exponent characterizes the rate at which brightness grows with luminance and can thus be thought of as an "exponential" gain factor. We studied changes in this gain factor for incremental and decremental test squares as a function of the size of a surrounding frame of homogeneous luminance. For incremental targets, the gain decreased as an approximately linear function of the frame width. For decremental targets, the gain increased as an approximately linear function of the frame width. We modeled the brightness of the frame-embedded target with a quantitative theory based on the assumption that the target brightness is determined by the sum of achromatic color induction signals originating from the inner and outer edges of the surround, a theory that has previously been used to account for the results of several other brightness matching experiments. To account for the frame-width-dependent gain changes observed in the present study, we elaborate this edge integration theory by proposing the existence of a cortical contrast gain control mechanism by which the gains applied to neural edge detectors are influenced by the responses of other edge detectors responding to the nearby edges.     

基于内外边缘颜色特征的图像检索算法

算法的基本思路是提取边缘部分的颜色特征进行图像检索,将边缘分为内外边缘区别对待,加大内边缘(对应目标部分)的比重,通过多尺度多结构元的数学形态学方法实现。通过设置内外边缘的权重充分考虑了目标的重要性,克服了全局颜色直方图不能反映空间信息的缺陷。实验结果表明,该算法有效地提高了检索系统的效率。     

Color‐edge detection based on discrimination of noticeable color contrasts

Color‐edge detection is an important research task in the field of image processing. Efficient and accurate edge detection will lead to higher performance of subsequent image processing techniques, including image segmentation, object‐based image coding, and image retrieval. To improve the performance of color‐edge detection while considering that human eyes are ultimate receiver of color images, the perceptually insignificant edges should avoid being over‐detected. In this article, a color‐edge detection scheme based on the perceptual color contrast is proposed. The perceptual color contrast is defined as the visible color difference across an edge in the CIE‐Lab color space. A perceptual metric for measuring the visible color difference of a target color pixel is defined by utilizing the associated perceptually indistinguishable region. The perceptually indistinguishable region for each color pixel in the CIE‐Lab color space is estimated by the design of an experiment that considers the local property due to local changes in luminance. Simulation results show that the perceptual color contrast is effectively defined and the color edges in color images are detected while most of the perceptually insignificant edges are successfully suppressed through the proposed color‐edge detection scheme. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 332–339, 2009     

Contrast edge colors under different natural illuminations

Essential to sensory processing in the human visual system is natural illumination, which can vary considerably not only across space but also along the day depending on the atmospheric conditions and the sun's position in the sky. In this work, edges derived from the three postreceptoral Luminance, Red-Green, and Blue-Yellow signals were computed from hyperspectral images of natural scenes rendered with daylights of Correlated Color Temperatures (CCTs) from 2735 to 25,889 K; for low CCT, the same analysis was performed using Planckian illuminants up to 800 K. It was found that average luminance and chromatic edge contrasts were maximal for low correlated color temperatures and almost constants above 10,000 K. The magnitude of these contrast changes was, however, only about 2% across the tested daylights. Results suggest that the postreceptoral opponent and nonopponent color vision mechanisms produce almost constant responses for color edge detection under natural illumination.     

Ultrasonic edge shadowing around cylindrical cavities with and without walls

In B-mode ultrasound images, the speckle distal to the edges of cavities of contrasting speed of sound (SOS) can be imprinted with a pattern characteristic of the cavity. This pattern, termed edge shadowing, is likely to involve alteration of both the speckle amplitude and its correlation length. Using the acoustic field calculated from the exact solution to the wave equation, we have simulated the ensemble-averaged speckle amplitude in B-mode images of cylindrical cavities both with and without walls, and compared the results to a simpler ray-based model. The simulations show that edge shadowing is caused predominantly by contrasts of the SOS, rather than of the density. The shadows on both walled and wall-less cylinders, for a focused incident beam, grow darker as the magnitude of the SOS contrast increases over a range up to +/- 10%. Extra shadows, caused by the inner wall boundary, appear on images of walled cylinders. The ray-based model agrees well with the wave model except in the shadow regions, within which the complexity of the phenomena seems to require the wave model.     

基于图像抽样的快速虹膜定位算法

提出了一种基于图像抽样的快速虹膜定位算法.首先在抽样图像中搜索瞳孔内一点,并以该点为起点检测粗略的虹膜内边缘点,然后在原分辨力图像中利用梯度算子精确定位内边缘点从而实现内边缘定位;虹膜外边缘定位采用Canny算子和Hough变换实现,由于基于抽样图像进行边缘提取,忽略了虹膜纹理等细节边缘信息,减少了大量外边缘干扰,提高了算法实时性.实验结果表明该算法的定位准确率达到99.47%,定位速度为0.162s.与经典的虹膜定位算法相比,该算法的定位速度有了很大提高.     

Effective contrast of colored stimuli in the mesopic range: a metric for perceived contrast based on achromatic luminance contrast

Little is known about how color signals and cone- and rod-based luminance signals contribute to perceived contrast in the mesopic range. In this study the perceived contrast of colored, mesopic stimuli was matched with that of spatially equivalent achromatic stimuli. The objective was to develop a metric for perceived contrast in the mesopic range in terms of an equivalent achromatic luminance contrast, referred to here as effective contrast. Stimulus photopic luminance contrast, scotopic luminance contrast, and chromatic difference from the background all contributed to effective contrast over the mid-mesopic range, but their contributions were not independent and varied markedly with background luminance. Surprisingly, color made a significant contribution to effective contrast from 10 to approximately 0.003 cd m(-2). A model describing this relationship is introduced (R2 = 0.89) and compared with predictions of mesopic luminance contrast obtained from a number of models proposed as systems of mesopic photometry.     

Local versus global contrasts in texture segregation

In a texture pair (TP) yielding a vertical or horizontal edge, the local (luminance or color) contrast or the local orientation of the individual textels is traded off with the global strength of the luminance-, color-, or orientation-defined TP edge so as to keep the latter at the detection threshold. Local and global contrasts are defined along the same (within-domain conditions) or along distinct physical dimensions (transdomain conditions). In the latter case local luminance or color contrast is traded off against global orientation. In all cases TP's are presented for 66.7 or 333.3 ms. Textels differ from the background in either luminance or color so that the TP's are respectively equichromatic or equiluminant. TP edge strength is modulated by means of swapping variable proportions of textels between the two textures in the TP. The observed local--global relationships are fitted with a version of the equivalent noise model for contrast coding modified to include the presentation time factor. The extension of the standard model in the time domain is meant to allow comparison between equivalent noise estimates for variable duration stimuli. Model fits of the within-domain data yield equivalent noise energy values significantly different for color- and luminance-defined TP's but are not applicable for the transdomain experiments, which indicates that global orientation processing is independent of both local luminance and local color contrast insofar as the latter are above the detection threshold. Finally, this study points to the equivalence among the local--global, the equivalent noise, and the statistical approaches to texture segregation.     

Ideal cue combination for localizing texture-defined edges

Many visual tasks can be carried out by using several sources of information. The most accurate estimates of scene properties require the observer to utilize all available information and to combine the information sources in an optimal manner. Two experiments are described that required the observers to judge the relative locations of two texture-defined edges (a vernier task). The edges were signaled by a change across the edge of two texture properties [either frequency and orientation (Experiment 1) or contrast and orientation (Experiment 2)]. The reliability of each cue was controlled by varying the distance over which the change (in frequency, orientation, or contrast) occurred-a kind of "texture blur." In some conditions, the position of the edge signaled by one cue was shifted relative to the other ("perturbation analysis"). An ideal-observer model, previously used in studies of depth perception and color constancy, was fitted to the data. Although the fit can be rejected relative to some more elaborate models, especially given the large quantity of data, this model does account for most trends in the data. A second, suboptimal model that switches between the available cues from trial to trial does a poor job of accounting for the data.     

改进的自适应阈值Canny边缘检测

针对传统Canny边缘检测算法的阈值需要人为设定的缺陷,本文提出了一种新的自适应改进方法.该方法-根据梯度直方图信息,提出梯度差分直方图的概念,同时,对图像进行自适应分类处理,使得算法不仅不需人工设定阈值参数,而且还能有效地避免Canny算法在边缘寻找中的断边和虚假边缘现象.对边缘信息丰富程度不同的灰度图和彩色图像运用该方法寻找边缘的实验结果表明,对于在目标与背景交界处的多数像素梯度幅值较大的图片,该算法具有边缘检测能力强、自适应能力强的优点.     

Effects of surround articulation on lightness depend on the spatial arrangement of the articulated region

We investigated the effect of surround articulation on the perceived lightness of a target disk. Surround articulation was manipulated by varying either the number of wedges in a surround consisting of wedges of alternating luminance or the number of checks in a surround consisting of a radial checkerboard pattern. In most conditions, increased articulation caused incremental targets to appear lighter and decremental targets to appear darker. But increasing the surround articulation in a way that did not increase the number of target-coaligned edges in the display did not affect the target lightness. We propose that the effects of surround articulation depend on the relationship between the orientations and contrast polarities of the target edges and those of edges present within the surround.     

Spatial-frequency-tuned mechanisms of the red-green channel estimated by oblique masking

The sustained spatial-frequency-tuned (SF-tuned) mechanisms of nonoriented units were examined by means of orthogonal masking for the Red-Green (R-G) color channel, and those of oriented units by oblique masking for the achromatic channel but not for the color channels. An oblique-masking technique minimizes the artifacts that are due to spatial phase effects, local cues, spatial beats, spatial probability summation, and changing criteria. Therefore the spatial characteristics of the R-G color channel are now investigated by an oblique-masking technique and linked with my paper on orthogonal masking [J. Opt. Soc. Am. A 15, 1 (1998)]. The R-G channel was defined by the minimum-flicker and hue-cancellation techniques. A color monitor system was used to generate spatially localized (D6) vertical color test patterns [0.063-8 cycles per degree (cpd)] and sinusoidal oblique color masks (0.031-16 cpd, 1.2-60% contrasts). Color contrast sensitivity functions (CSFs), threshold elevation (TE) versus mask SF (TvSF) curves, and TE versus mask contrast (TvC) curves were measured by the method of constant stimuli with a two-interval forced-choice technique by using Powell's achromatizing lens under sustained (Gaussian, 2-s-duration) conditions. Results show the following: (1) The color CSF is a low-pass function of SF with average half-height SF of 0.7 cpd and cutoff SF of 14 cpd with the use of a color-detection criterion. (2) TvSF curves are broadly bandpass and fall into five groups, peaking at approximately 0.13, 0.5, 2, 4, and 8 cpd. The root-mean-square cone-color CSF is 3.8-5.4 times the stimulus-color CSF. (3) A "crowding effect" similar to that of the TvSF curves of the achromatic channel was also found, but the TvSF curves of the R-G channel are not sharply peaked, similar to the result for orthogonal masking. Data analysis led to the following conclusions: (1) A simple multiple-mechanism model yields one low-pass color mechanism (with average half-height SF of 0.54 cpd) and five bandpass SF-tuned color mechanisms; these six mechanisms are necessary to explain the CSF, TvSF, and TvC data simultaneously. (2) The bandpass mechanisms peaked at approximately 0.13, 0.5, 2, 4, and 8 cpd with average full bandwidths at half-heights of 3.6, 3.2, 2.1, 1.2, and 1.3 octaves, respectively. (3) Since oblique-masking color mechanisms (unlike achromatic oriented mechanisms) have broad orientation tuning under sustained conditions and there is a significant orthogonal masking, the oblique-masking color mechanisms may have contributions from both oriented and nonoriented units. (4) The high degree of similarity between the SF-tuned filters of mechanisms derived from oblique- and orthogonal-masking data suggests that most of the chromatic SF tuning is already accomplished by nonoriented units. (5) The quality of the fit to oblique- and orthogonal-masking data combined dropped enough to reject the hypothesis that the former taps the performance of only the same nonoriented mechanisms as those by the latter. Adding gain parameters that reduce the TEs for orthogonal masking gave a better fit, suggesting that orientation gains are one of the factors involved in the transformation of information from nonoriented to oriented mechanisms. However, the fit was still worse than that for oblique-(6) Since masking-alone or orthogonal-masking-alone data, suggesting that more factors may be involved. primate parvo lateral geniculate nucleus (pLGN) units behave in a fairly linear manner, the color contrast nonlinearity (which follows the linear filter) of a mechanism may be post-pLGN.     

有局部缺陷的滚动体中介轴承动力学建模及仿真研究

在考虑径向间隙及滚动体缺陷通过内、外圈时接触变形量发生变化基础上,建立两种支承形式下滚动体含单一故障缺陷的中介轴承动力学模型。对比研究不同支承形式及内、外圈不同旋转方向对中介轴承振动影响。结果表明,采用内圈支承于高压转子、外圈支承于低压转子结构振幅大于内圈支承于低压转子、外圈支承于高压转子结构;内、外圈同向旋转振幅大于反向旋转;内、外圈反向旋转冲击振幅小不利于发现故障,反向旋转时缺陷冲击滚道频繁,同等运行条件下,反向旋转中介轴承潜在危险更大;保持架旋转频率为中介轴承振动信号的主要调制频率,且内、外圈反向旋转较同向旋转调制效果更强烈。     

Importance of color in the segmentation of variegated surfaces

We examined how variations in color and brightness are used by the visual system in distinguishing textured surfaces that differed in their first- or second-order statistics. Observers viewed a 32 x 32 array containing two types of square elements differing in chromaticity or luminance or both. The spatial distributions of the two kinds of elements were varied within the array until observers could distinguish two juxtaposed regions. At low but not at high contrast, observers are better able to distinguish regions when the elements differ only in chromaticity than when they differ only in luminance. The advantage of color at low contrasts results from the greater visibility of the arrays defined by color variation. An observer's capacity to distinguish textures defined by variations in first-order chromatic statistics is little affected by the addition of achromatic noise but is more affected by the addition of chromatic noise. The relative robustness of chromatic cues in the face of achromatic noise leaves the visual system well equipped to exploit color variations in segmenting complex scenes, even in the presence of variations in brightness. This capacity seems to depend on mechanisms that sum over large regions: When surfaces differ in their second-order statistics and cannot be distinguished by mechanisms that sum over large regions, the advantage of color is much diminished.     

纹理贴图模型的彩色截面轮廓生成算法研究

针对彩色3D打印彩色轮廓生成问题,本文提出一种基于纹理贴图模型的彩色轮廓生成算法。根据平面投影法建立纹理和三维模型的映射关系,接着对该模型进行切片处理取得轮廓顶点的几何信息和纹理信息;并根据轮廓顶点和纹理图片的映射关系,插值出顶点间色彩信息;同时给出一种内外轮廓的快速识别算法,并提出一种基于偏置算法的彩色轮廓偏置方法,形成颜色厚度,消除阶梯效应。     

Color image sharpening inspired by human vision models

A method to sharpen digital color images that takes viewing conditions and human vision models into consideration is described. The method combines the Laplacian of Gaussian (LoG) operator with spatial filters that approximate the contrast sensitivity functions of human visual systems. The sharpening operation is introduced in the opponent color space, following the scheme proposed in the spatial extension of CIELAB (S-CIELAB). We deduce the modification of the original image necessary to obtain the spatially filtered image that approaches the perceived LoG-sharpened image for given viewing conditions. At short viewing distances, for which the spatial blurring is small, most fine edges and object contours are sharpened. At long distances, for which the spatial blurring is greater, only large figures are sharpened. Because of the smoothing Gaussian functions involved in the LoG operator, the proposed image sharpening does not tend to increase noise. When the sharpening operation is limited to the achromatic channel, the results are good. This is consistent with the high importance attached to the luminance channel in the spatial content of color images. Image sharpening based on only the Laplacian of the original is not sensitive to variations of viewing conditions, tends to increase noise, and suffers from its appearance deteriorating rather quickly with the depth of the sharpening operation.     

一种求含孔洞多边形交、并、差集的新方法

提出了一种基于最小回路确定含孔洞多边形P和Q的交、并、差集的新方法.首先,初始化P和Q外环为逆时针方向,内环为顺时针方向,并通过连接内环极右顶点与其在外环上一可见点v,构造一条双向“桥边”,将内外多环转换为单环.其次,求出P和Q被转换为单环的边序列的交点,并对交点处的关联边进行排序.然后,沿着各个交点处正向边,依照最小转角原则搜索最小回路,并根据其中所含P和Q边所呈现的顺、逆时针方向进行分类.最后,P和Q的交、并、差集即对应不同类别的最小回路.算法简洁且几何意义明显,具有较好的适应性.     

振动机械滚动轴承两点点蚀故障诊断研究

针对振动机械滚动轴承两点点蚀故障的判别问题,建立了基于Hertz接触理论的振动机械滚动轴承内环和外环两点点蚀故障的振动模型,提出了两点点蚀故障的判别依据,对理论模型进行了仿真,并在振动筛上进行了试验研究。理论分析与试验分析结果一致表明,振动机械与旋转机械滚动轴承两点点蚀的故障特征频谱有明显的区别。振动机械滚动轴承外环点蚀故障时有明显的振幅调制现象,而理想的旋转机械外环点蚀无振幅调制现象;振动机械滚动轴承内环点蚀故障时有轻微的振幅调制现象,而理想的旋转机械内环点蚀存在明显的振幅调制现象。     

Color Edge Detection Using Multidirectional Sobel Filter and Fuzzy Fusion

A new model is proposed in this paper on color edge detection that uses the second derivative operators and data fusion mechanism. The second-order neighborhood shows the connection between the current pixel and the surroundings of this pixel. This connection is for each RGB component color of the input image. Once the image edges are detected for the three primary colors: red, green, and blue, these colors are merged using the combination rule. Then, the final decision is applied to obtain the segmentation. This process allows different data sources to be combined, which is essential to improve the image information quality and have an optimal image segmentation. Finally, the segmentation results of the proposed model are validated. Moreover, the classification accuracy of the tested data is assessed, and a comparison with other current models is conducted. The comparison results show that the proposed model outperforms the existing models in image segmentation.     

深沟球轴承运转过程动态特性有限元分析

综合考虑轴承径向载荷及转速的影响,应用ANSYS/LS-DYNA软件建立了深沟球轴承多体动力接触有限元模型;以显式动力学有限元法为基础,采用全积分单元算法控制沙漏,设置质量缩放系数缩减计算时间,对内圈施加不同转速时的深沟球轴承进行动力接触分析,得出了深沟球轴承运转过程的动态响应及滚动体的应力分布。滚动体的最大和最小线速度分别出现在与内、外圈接触点上,各转速下滚动体与内圈接触的应力基本相同,滚动体与外圈接触的应力随转速增高而相应增大,滚动体与外圈间接触力的波动大于内圈,而滚动体与保持架间的作用力较小。研究表明,ANSYS/LS-DYNA是分析轴承运转过程动力接触问题十分有效的工具。