Image segmentation and lightness perception

The perception of surface albedo (lightness) is one of the most basic aspects of visual awareness. It is well known that the apparent lightness of a target depends on the context in which it is embedded, but there is extensive debate about the computations and representations underlying perceived lightness. One view asserts that the visual system explicitly separates surface reflectance from the prevailing illumination and atmospheric conditions in which it is embedded, generating layered image representations. Some recent theory has challenged this view and asserted that the human visual system derives surface lightness without explicitly segmenting images into multiple layers. Here we present new lightness illusions--the largest reported to date--that unequivocally demonstrate the effect that layered image representations can have in lightness perception. We show that the computations that underlie the decomposition of luminance into multiple layers under conditions of transparency can induce dramatic lightness illusions, causing identical texture patches to appear either black or white. These results indicate that mechanisms involved in decomposing images into layered representations can play a decisive role in the perception of surface lightness.     

具有细节补偿和色彩恢复的多尺度Retinex色调映射算法

针对带色彩恢复的多尺度Retinex色调映射算法(MSRCR)在分离图像光照信息时未保留部分细节信息,导致结果图像出现细节模糊和颜色失真的问题,提出了一种具有细节补偿和色彩恢复的多尺度Retinex色调映射算法(MSRCD).该算法利用Retinex理论的基本原理将高动态范围图像分为反射层和光照层,先使用双边滤波从图像光照层中提取出细节信息进行补偿,然后从图像的反射层中分离出基本层信息并进行自适应调整,压缩其动态范围,最后通过色彩校正还原图像颜色.实验结果表明,与MSRCR算法及基于双边滤波的算法相比,MSRCD算法的处理结果保留了更丰富的细节信息,色彩逼近于真实场景且避免了光晕的产生.     

基于多元回归的色彩人格定量化研究

色彩是视觉感知的重要组成,它不仅具有美学价值,还能激起对人格特质的联想,即色彩人格.然而,目前仍缺乏对色彩与其激起的人格特质联想之间关系的定量化描述.本研究首次对色彩属性与人格联想间的定量化关系进行研究,采用语义差分法获取了色彩激起的人格联想,基于多元回归建立了色彩人格模型.结果表明,色彩的明度,浓度和色相对人格特质的感知都具有影响;而且,色彩的属性及其激起人格联想之间的关系能够较好地被多元回归模型定量化.该结果为虚拟角色的色彩人格设计提供了依据.     

计算机视觉系统的二步法颜色恒常性

理论研究表明 ,三色视觉系统在单视野条件下 ,三维颜色恒常性的计算问题只有在一些约束下才能解决。约束选择的合理与否和后续的任务密切相关。针对不同环境光照条件下的人体肤色分割的具体任务 ,提出了一个新的关于三色系统颜色恒常性问题的物理模型 :1 )将视觉系统所获得的原始信息分裂为亮度信息和颜色信息。 2 )将传统的颜色恒常性问题分解为基于亮度的亮度恒常性和基于颜色信息的颜色恒常性 ,并用二维描述子描述等亮度彩色图像中物理表面的颜色特征。该描述子具有颜色恒常的特性。基于颜色的图像分割实验结果表明 ,二步法颜色恒常性技术是一种非常有效的方法。     

Perceived luminance depends on temporal context

Brightness--the perception of an object's luminance--arises from complex and poorly understood interactions at several levels of processing. It is well known that the brightness of an object depends on its spatial context, which can include perceptual organization, scene interpretation, three-dimensional interpretation, shadows, and other high-level percepts. Here we present a new class of illusion in which temporal relations with spatially neighbouring objects can modulate a target object's brightness. When compared with a nearby patch of constant luminance, a brief flash appears brighter with increasing onset asynchrony. Simultaneous contrast, retinal effects, masking, apparent motion and attentional effects cannot account for this illusory enhancement of brightness. This temporal context effect indicates that two parallel streams--one adapting and one non-adapting--encode brightness in the visual cortex.     

Image statistics and the perception of surface qualities

The world is full of surfaces, and by looking at them we can judge their material qualities. Properties such as colour or glossiness can help us decide whether a pancake is cooked, or a patch of pavement is icy. Most studies of surface appearance have emphasized textureless matte surfaces, but real-world surfaces, which may have gloss and complex mesostructure, are now receiving increased attention. Their appearance results from a complex interplay of illumination, reflectance and surface geometry, which are difficult to tease apart given an image. If there were simple image statistics that were diagnostic of surface properties it would be sensible to use them. Here we show that the skewness of the luminance histogram and the skewness of sub-band filter outputs are correlated with surface gloss and inversely correlated with surface albedo (diffuse reflectance). We find evidence that human observers use skewness, or a similar measure of histogram asymmetry, in making judgements about surfaces. When the image of a surface has positively skewed statistics, it tends to appear darker and glossier than a similar surface with lower skewness, and this is true whether the skewness is inherent to the original image or is introduced by digital manipulation. We also find a visual after-effect based on skewness: adaptation to patterns with skewed statistics can alter the apparent lightness and glossiness of surfaces that are subsequently viewed. We suggest that there are neural mechanisms sensitive to skewed statistics, and that their outputs can be used in estimating surface properties.     

Influence of scene statistics on colour constancy

The light reflected from an object depends not only on the surface properties of this object but also on the illuminant. The same is true for the excitations of the photoreceptors, which serve as the basis for the perceived colour. However, our visual system has the ability to perceive constant surface colours despite changes in illumination. The average chromaticity of the retinal image of a scene depends on the illumination, and thus might be used by the visual system to estimate the illumination and to modulate the correction that subserves colour constancy. But this measure is not sufficient: a reddish scene under white light can produce the same mean stimulation as a neutral scene in red light. Higher order scene statistics-for example, the correlation between redness and luminance within the image-allow these cases to be distinguished. Here we report that the human visual system does exploit such a statistic when estimating the illuminant, and gives it a weight that is statistically appropriate for the natural environment.     

Neural synchrony correlates with surface segregation rules

To analyse an image, the visual system must decompose the scene into its relevant parts. Identifying distinct surfaces is a basic operation in such analysis, and is believed to precede object recognition. Two superimposed gratings moving in different directions (plaid stimuli) may be perceived either as two surfaces, one being transparent and sliding on top of the other (component motion) or as a single pattern whose direction of motion is intermediate to the component vectors (pattern motion). The degree of transparency, and hence the perception, can be manipulated by changing only the luminance of the grating intersections. Here we show that neurons in two visual cortical areas--A18 and PMLS--synchronize their discharges when responding to contours of the same surface but not when responding to contours belonging to different surfaces. The amplitudes of responses correspond to previously described rate predictions for component and pattern motion, but, in contrast to synchrony, failed to reflect the transition from component to pattern motion induced by manipulating the degree of transparency. Thus, dynamic changes in synchronization could encode, in a context-dependent way, relations among simultaneous responses to spatially superimposed contours and thereby bias their association with distinct surfaces.     

面向管道焊缝渗透检测机器人的管道定位与规划方法

为了实现核电设施管路的自动化焊缝检测作业,在降低人工作业安全风险的同时提高工作效率,提出了一种集喷涂、喷擦、刷涂、擦洗、环境感知和场景建模的机器人自主作业软件系统及相关算法。分析作业机器人的工作环境和功能需求,进行机械臂和感知模块的选型,制定三维建模和参数辨识方案,搭建焊缝检测作业系统;提出了一种基于机器人感知到的视觉和深度信息进行场景建模的算法,该算法可以输出检测关到作业面的位置、三维模型以及作业区域范围;提出了一种基于三维重构模型和作业区域范围进行作业轨迹规划的算法,并搭建了仿真平台验证运动轨迹的正确性;开展了管道定位与三维重构实验以及轨迹规划实验,实验的结果证明,提出的管道定位方法能够实现精确的点云数据采集和高精度的管道参数辨识,机械臂能够实现准确性高、连续性好的运动,满足管道焊缝检测作业的要求。     

亮度和色度加工在视觉感受器水平上的独立性

目的：在视觉系统感受器水平上研究色度和亮度加工的独立性．方法：让12名先天性红色觉异常者进行短暂呈现的色度鉴别和亮度鉴别实验．结果：发现那些不能感受红颜色色度的受试者，但能感受等亮度的红色和灰色的亮度．结论：当色觉感受器异常者的红色觉完全丧失时，其感受伴随色度的亮度的能力依然存在．因此,在视觉感受器水平上的色度和亮度加工是独立的．     

Perception of three-dimensional shape influences colour perception through mutual illumination

Objects in the natural world possess different visual attributes, including shape, colour, surface texture and motion. Previous perceptual studies have assumed that the brain analyses the colour of a surface independently of its three-dimensional shape and viewing geometry, although there are neural connections between colour and two-dimensional form processing early in the visual pathway. Here we show that colour perception is strongly influenced by three-dimensional shape perception in a novel, chromatic version of the Mach Card--a concave folded card with one side made of magenta paper and the other of white paper. The light reflected from the magenta paper casts a pinkish glow on the white side. The perceived colour of the white side changes from pale pink to deep magenta when the perceived shape of the card flips from concave to convex. The effect demonstrates that the human visual system incorporates knowledge of mutual illumination-the physics of light reflection between surfaces--at an early stage in colour perception.     

基于视觉感知的LCDs运动图像边缘模糊的评价方法

基于LCD运动图像锐度的视觉感知实验,采用线性回归的方法,得到人眼感知到的运动图像边缘锐度参量Zscore的计算表达式,提出了利用与边界斜率和过驱动相关的2个参数来描述运动图像边缘模糊程度的量化公式.并将计算预测值和视觉感知的实验值进行比较.结果表明,二者具有较高的相关性(R2≥0.8892),该量化公式可以很好地用于...     

可见光与红外灰度融合图像感知对比度客观评价

如何客观有效地评价融合图像质量,是融合技术发展与装备应用面临的一个关键问题.图像对比度是衡量双波段灰度融合质量的一项重要的评价指标.针对目前的图像对比度客观计算模型没有充分反映人眼视觉特性,从而影响模型计算结果与人眼视觉感受的一致性的问题.在各向同性局部对比度计算模型基础上,引入人眼视觉的亮度掩盖特性,提出图像感知对比度客观评价模型.使用模拟灰度图像以及人眼主观评价实验得到的15组不同真实场景融合图像的对比度评价数据来验证客观计算模型.结果表明,相比于4种经典的对比度客观评价模型,建立的图像感知对比度模型评价结果更符合人眼视觉感受,可以有效实现双波段灰度融合图像感知对比度的客观评价.      

Does the brain know the physics of specular reflection?

Images of artificial and natural scenes typically contain many highlights generated by mirror-like reflection from glossy surfaces. Until recently, computational models of visual processes have tended to regard highlights as obscuring the structure of the underlying scene. The truth is that, on the contrary, highlights are rich in local geometric information. Here we report that the three-dimensional appearance of a highlight on a computer-simulated stereoscopic curved surface affects observers' judgment of surface gloss. We also show that the 3-D appearance of a highlight affects the perception of surface curvature--that is, it can force an ambiguous convex-concave figure to change state. We thus conclude that human visual analysis seems to employ a physical model of the interaction of light with curved surfaces, a model firmly based on ray optics and differential geometry.     

A computational theory for the perception of coherent visual motion

When we see motion, our perception of how one image feature moves depends on the behaviour of other features nearby. In particular, the Gestaltists proposed the law of shared common fate, in which features tend to be perceived as moving together, that is, coherently. Recent psychophysical findings, such as the cooperativity of the motion system and motion capture, support this law. Computationally, coherence is a sensible assumption, because if two features are close then they probably belong to the same object and thus tend to move together. Moreover, the measurement of local motion may be inaccurate and so the integration of motion information over large areas may help to improve the performance. Present theories of visual motion, however, do not account fully for these coherent motion percepts. We propose here a theory that does account for these phenomena and also provides a solution to the aperture problem, where the local information in the image flow is insufficient to specify the motion uniquely.     

Simulating Human Visual Perception in Nighttime Illumination

This paper presents an image-based algorithm for simulating the visual adaptation of the human visual system to various illuminations,especially in dark nighttime conditions.The human visual system exhibits different characteristics depending on the illumination intensity,with photopic vision in bright conditions,scotopic vision in dark conditions,and mesopic vision between these two.A computational model is designed to simulate multiple features of mesopic vision and scotopic vision,including the chromaticity change,luminance change,and visual acuity loss.The system uses a source image under bright illumination as input.Then assuming that the viewer has already adapted to the new conditions,the color spectrum of the input image is reconstructed to replace the source with modifications of the chromaticity and the luminance of the relighted scene.A bilateral filter is used to simulate the visual acuity loss.The model parameters have clear physical meanings and can be obtained from experimental data to achieve realistic results.The algorithm can be used not only for visual perception simulation,but also as a day-for-night tool to produce realistic nighttime images from daytime images.     

视频序列中基于肤色的人脸实时检测

利用肤色在颜色空间的聚类特性来检测人脸,为了去除亮度对肤色的影响,增强检测的可靠性,采用了同时在RGB归一化颜色空间和HSV颜色空间中对肤色进行检测.在肤色检测之前采用了图像差分法先检测出运动空间,消除了背景对肤色检测的影响,也缩小了肤色搜索的范围.关于实际场景的实验表明,本文算法既能准确地检测出人脸,同时又能够达到实时效果.     

基于拓扑图及三维特征的三维物体识别方法

提出一种基于拓扑图及三维特征的三维物体识别方法.该方法在图象预处理阶段先检测物体可视表面的闭合边界,再依据闭合边界对物体进行表面分割,并用一个景物特征图对景物进行表达(SAGR).在建模阶段,先采用多视图表面模型方法建模,再依据表面分割,对模型用一个模型特征图进行表达(MAGR).在物体识别阶段,将景物与模型的匹配分3部分进行,即扫描部件、图的匹配部件及匹配检验部件.匹配首先是基于 SAGR 与 MAGR 图的拓扑性质的匹配,然后是基于三维特征的匹配.根据匹配结果,或对未知物体自动建模,或给出识别结果.     

Auditory distance perception in rooms

The perceived distance of a sound source in a room has been shown to depend on the ratio of the energies of direct and reflected sound. Although this relationship was verified in later studies, the research has never led to a quantitative model. The advent of techniques for the generation of virtual sound sources has made it possible to study distance perception using controlled, deterministic stimuli. Here we present two experiments that make use of such stimuli and we show that a simple model, based on a modified direct-to-reverberant energy ratio, can accurately predict the results and also provide an explanation for the 'auditory horizon' in distance perception. The modification of the ratio consists of the use of an integration time of 6 milliseconds in the calculation of the energy of the direct sound. This time constant seems to be important in spatial hearing-the precedence effect is also based on a similar integration window.     

扩展的G-KRA抽象模型

将广义知识重构与抽象模型框架下的初步感知过程扩展为多重感知过程, 根据物理世界W中对象所属域的不同生成多重域抽象模型, 并讨论了两种情况下域抽象模型Wi和Wj间的域关系： W的多重域模型W_i和W_j中的构成对象交集为空（即W_i和W_j中不存在有跨域行为的实体）; W的多重域模型W_i和W_j中的对象实体存在跨域行为. 扩展后的框架R丰富了物理世界W的模型表示, 使对象感知由平面感知变为立体感知, 应用多种领域知识生成相互关联的不同域模型, 增强了模型的推理能力.