Search

In order to improve classification performance of the hash algorithm for color images, this paper presents an hash algorithm that based on three-dimensional color structure features and luminance gradient feature. Firstly, the algorithm preprocesses the input image to produce a secondary image, and extracts the color opponent component from the secondary image. Secondly, three-dimensional external structural features are constructed by using the peak curve, mean curve, and valley curve of the color opponent component. Thirdly, the overlapping points of the peak points in different visual angles and the valley points in different visual angles are selected as the salient points. The position information of the salient points are used to construct internal features. The gradient feature is constructed by using pixel changes in four directions of Y component of luminance image in YCbCr color space. Finally, the three-dimensional color structure features and luminance gradient feature are combined and disturbed to obtain the final hash sequence. Experiment results show that the proposed scheme has preferable robustness and discrimination. Compared with some existing schemes, the proposed scheme has better classification performance, shorter hash length and less average time of hash generation, and it has good detection performance in image copy detection and image tampered detection.

The glare effect is a brightness illusion that has captured the attention of the vision community since its discovery. However, its photometrical reversal, which we refer to here as photometrical reversed glare (PRG) stimuli, remained relatively unexplored. We presented three experiments that sought to examine the perceived brightness of a target area surrounded by luminance gradients in PRG stimuli and compare them with conventional glare effect configurations. Experiment 1 measured the brightness of the central target area of PRG stimuli through an adjustment task; the results showed that the target appeared brighter than similar, comparative areas not surrounded by luminance gradients. This finding was unexpected given the recent report that PRG stimuli cause pupil dilation. Meanwhile, Experiments 2 and 3 implemented a rating task to further test the findings in Experiment 1. Again, the study found a robust brightening illusion in the target area of PRG stimuli in a wide range of target and background luminance. The results are discussed in comparison with the brightness enhancement of the glare effect. [ABSTRACT FROM AUTHOR]

The feeling of being dazzled that is evoked by images consisting of an achromatic uniform center surrounded by regions with a luminance gradient was investigated. The effects of type of color saturation gradient in the peripheral region on the feeling of being dazzled were examined. Stimulus configuration was also varied. For the stimulus configuration of a disk-annulus, the feeling of being dazzled was lower for an increasing saturation gradient from the center to the periphery than for decreasing and no-saturation gradients when the center and the periphery maximum luminances were the same. This suggests that the presence of a chromaticity difference between the disk and the surrounding annulus strengthens the feeling of being dazzled. Similar results were obtained for the stimulus configuration of a star shape. For the stimulus configuration of a cross shape, quite different results were obtained; the chromaticity discontinuity had little or opposite effect. These results suggest that chromaticity border and stimulus configurations are factors in the feeling of being dazzled that is evoked by images with luminance gradient. [ABSTRACT FROM AUTHOR]

The feeling of being dazzled is evoked by images consisting of an achromatic uniform center, surrounded by regions with luminance gradients. As the perceptual distinctness of the central region has been suggested to contribute to the feeling of being dazzled, we examined the effects of a gap between the central and surrounding regions on the feeling of being dazzled. The stimulus comprised a disk with uniform luminance surrounded by an annulus, of which the luminance was decreased from the inner boundary to the periphery. Three luminance profiles (linear, logistic, and inverse-logistic) of the surrounding luminance ramps were used. The distinctness of the disk decreased in the order of logistic, linear, and inverse-logistic profiles. The luminance of the disk, the maximum luminance of the annulus, and the gap size were also varied. When the luminance continuously transitioned from the disk to the annulus, the feeling of being dazzled was stronger for the inverse-logistic annulus luminance profile, compared with the logistic and linear profiles without a gap; however, it was not different for the three profiles with a gap. Further, the feeling of being dazzled increased when a gap was introduced for the logistic and linear profiles, but not for the inverse-logistic profile. These results suggest that the feeling of being dazzled was reduced by the perceptual indistinctness of the central disk for the logistic and linear annulus luminance profiles, while the gap restored the feeling of being dazzled by making the central disk perceptually distinct., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2023.)

Accurate perception of surface reflectance poses a significant computational problem for the visual system. The amount of light reflected by a surface is affected by a combination of factors including the surface’s reflectance properties and illumination conditions. The latter are not limited by the strength of the illuminant but also include the relative placement of the light illuminating the surface, the orientation of the surface and its 3d shape, all of which result in a pattern of luminance gradients across the surface. In this study we explore how luminance gradients contribute to lightness perception. We introduce a novel, simple lightness illusion. It consists of six separate checks, organized in rows of two. Each check has a negative luminance gradient across it. The top and the bottom rows are the same: with the darker check on the left, and the lighter check on the right. Two checks in the middle row are identical; however, the check on the right appears darker than the check on the left. As there are no shared borders between the checks, simultaneous contrast cannot explain the effect. However, there are multiple possible explanations including spatial filtering (Blakeslee & McCourt, 2004) or some higher-order mechanism such as perceptual grouping or amodal completion. Here, we explore these possibilities by manipulating the luminance configurations and the gradient slopes of the checks.

The Poggendorff illusion is one of the most exhaustively studied illusions. Can it be revived as an interesting problem? Perhaps by moving it to a slightly different domain. Here, we consider the occlusion of a subjectively linear ramp of tonal values. In a simple experiment, we find results closely resembling those of the geometrical Poggendorff. Yet, the "explanations" offered for the latter hardly apply to the former case. Depending upon one's perspective, this may be taken to "revive" the Poggendorff illusion. [ABSTRACT FROM AUTHOR]

Accurate perception of surface reflectance poses a significant computational problem for the visual system. The amount of light reflected by a surface is affected by a combination of factors including the surface's reflectance properties and illumination conditions. The latter are not limited by the strength of the illuminant but also include the relative placement of the light illuminating the surface, the orientation of the surface and its 3d shape, all of which result in a pattern of luminance gradients across the surface. In this study we explore how luminance gradients contribute to lightness perception. We introduce a novel, simple lightness illusion. It consists of six separate checks, organized in rows of two. Each check has a negative luminance gradient across it. The top and the bottom rows are the same: with the darker check on the left, and the lighter check on the right. Two checks in the middle row are identical; however, the check on the right appears darker than the check on the left. As there are no shared borders between the checks, simultaneous contrast cannot explain the effect. However, there are multiple possible explanations including spatial filtering (Blakeslee and McCourt, 2004) or some higher-order mechanism such as perceptual grouping or amodal completion. Here, we explore these possibilities by manipulating the luminance configurations and the gradient slopes of the checks. [ABSTRACT FROM AUTHOR]

In this paper we present some demonstrations concerning the width of Mach bands and henceforth hypothesize certain relations. We show that it is the variation in width of Mach bands in relation to luminance gradients which is responsible for Mach bands being strong for luminance ramps and weak or vanishing for luminance steps. We present the results of the experiments carried out by us using some of these demonstrations to provide support for our claims. [ABSTRACT FROM AUTHOR]

The feeling of dazzling that is evoked by luminance gradients was examined. The stimulus consisted of a disk with uniform luminance surrounded by an annulus whose luminance was decreased from the inner boundary to the periphery. Three luminance profiles (linear, logistic, and inverse logistic) of a surrounding luminance ramp were used. The luminance of the disk and the maximum luminance of the annulus were also varied. The feeling of dazzling became stronger as the luminance of the disk and the maximum luminance of the annulus increased. The effect of the maximum luminance of the annulus was greater for the disk with low luminance than for that with high luminance. The feeling of dazzling tended to be greater for the logistic profile than for the other profiles. However, when the luminance of the disk and that at the inner boundary of the annulus were the same, the feeling of dazzling for the logistic profile was no stronger than that for the linear or the inverse-logistic profile. These results suggest that smooth transition from the disk to the annulus for the logistic profile suppresses the feeling of dazzling. [ABSTRACT FROM AUTHOR]

A series of experiments were conducted to find the effects of non-uniform illumination on the surface-color mode perception. Two patterns of the illumination, one-sided illumination and a spotlight, were simulated. Observers adjusted the luminance of the test stimulus so that it just started to appear partially as an aperture-color mode. We found that the upper-limit luminance was significantly lower for all test colors when the directions of the gradient between the test stimulus and the surrounds did not match. On the other hand, in the spotlight conditions the upper-limit luminances changed only when it was contained in the spotlighted area. Our results suggest that the brightest stimulus in the scene does not work as a cue, and that the visual system takes the influence of illumination into account in order to set a criterion for the judgment for the color appearance of the mode. [ABSTRACT FROM AUTHOR]

SFS (Shape From Shading) theory is based upon the Lambertian paradigm. Our visual demonstrations imply that this paradigm fails to apply to the conventional stimuli used to probe vision.