Sensitivity to luminance and chromaticity gradients in a complex scene

Abstract

Image gradients--smooth changes in color and luminance--may be caused by intrinsic surface reflectance properties or extrinsic illumination phenomena, including shading, shadowing, and inter-reflections. In turn, image gradients may provide the visual system with information concerning the origin of these factors, such as the orientation of surfaces with respect to the light source. Color gradients induced by mutual illumination (MI) may play a similar role to that of luminance gradients in shape-from-shading algorithms; it has been shown that 3D shape perception modulates the influence of MI on surface color perception (M. G. Bloj, D. Kersten, & A. C. Hurlbert, 1999). In this study, we assess human sensitivity to changes in color and luminance gradients that arise from changes in the light source position, within a complex scene. In Experiment 1, we tested whether observers were able to discriminate between gradients due to different light source positions. We found that observers reliably detected a change in the gradient information when the light source position differed by only 4 deg from the reference scene. This sensitivity was mainly based on the luminance information in the gradient (Experiments 2 and 3). Some observers make use of the spatial distribution of chromaticity and luminance values within gradients when discriminating between them (Experiment 4). The high sensitivity to gradient differences supports the notion that gradients contain information that may assist in the recovery of 3D shape and scene configuration properties.

Rendering Techniques in 3D Computer Graphics Based on Changes in the Brightness of the Object Background

“…Meanwhile, the perception of total surface specularity and the perception of the background were discovered not to be so relevant during the observations. In addition, other authors have analysed many aspects of colour constancy and colour perception in 2D and 3D scenes [46][47][48][49].…”

Lightness Constancy in Surface Visualization

“…This provides an estimable lighting direction and increased depth cueing, both of which may enhance constancy effects over ambient occlusion alone [4], [19]. We anticipate that adding local directional lighting may improve color matching performance for surface visualization.…”

“…Lightness constancy is also sensitive to a variety of visual factors: in studies, simply moving from the real world to a virtual image has significantly impaired constancy [2]. Techniques commonly used in visualization, such as ambient occlusion lighting [3], may remove many visual cues that theoretical work indicates are used for lightness constancy, such as lighting direction [4]. …”

“…Existing theories hypothesize that properties such as contrast ratios between light and shadow [14], [15], shadow intensity [6], lighting intensity [16], lighting direction [4], object colors and reflectance [15], [17] and spatial cues [18], [19], [20], [21] may all contribute to the brain's ability to disentangle an object's color from the lighting used to illuminate it. For example, the visual system may identify a luminance value in a scene as an “anchoring point,” such as the lightest or average luminance value, and adjust perceptions of all residual colors accordingly [1].…”

Unbiased analysis of C. elegans behavior reveals the use of distinct turning strategies during magnetic Orientation

“…Behavioral strategies that allow animals to effectively orient to graded stimuli of different natures have been thoroughly studied (e.g. visual: el Jundi et al, 2014;Ruppertsberg et al, 2008;auditory: Teder-Sälejärvi and Hillyard, 1998;chemical: Pierce-Shimomura et al, 1999;and thermal: Kimata et al 2012). While behavioral strategies may differ depending on the type and shape of graded stimuli, they are similar in that information is derived from experienced spatiotemporal changes in stimulus intensity.…”