ABSTRACT
Brightness is one of the most important perceptual correlates of color appearance models (CAMs) when self-luminous stimuli are targeted. However, the vast majority of existing CAMs adopt the presence of a uniform background surrounding the stimulus, which severely limits their practical application in lighting. In this paper, a study on the brightness perception of a neutral circular stimulus surrounded by a non-uniform background consisting of a neutral ring-shaped luminous area and a dark surround is presented. The ring-shaped luminous area is presented with 3 thicknesses (0.33 cm, 0.67 cm and 1.00 cm), at 4 angular distances to the edge of the central stimulus (1.2°, 6.4°, 11.3° and 16.1°) and at 3 luminance levels (90 cd/m2, 335 cd/m2, 1200 cd/m2). In line with the literature, the results of the visual matching experiments show that the perceived brightness decreases in presence of a ring and the effect is maximal at the highest luminance of the ring, for the largest thickness and at the closest distance. Based on the observed results, an image-based model inspired by the physiology of the retina is proposed. The model includes the calculation of cone-fundamental weighted spectral radiance, scattering in the eye, cone compression and receptive field post-receptor organization. The wide receptive field assures an adaptive shift determined by both the adaptation to the stimulus and to the background. It is shown that the model performs well in predicting the matching experiments, including the impact of the thickness, the distance and the intensity of the ring, showing its potential to become the basic framework of a Lighting Appearance Model.
Subject(s)
Light , Vision, Ocular , Lighting , Retina/physiology , Visual Perception/physiologyABSTRACT
Recently, a color appearance model, CAM18sl, has been published. The model can predict the color perception (hue, colorfulness, brightness) of self-luminous stimuli seen against neutral backgrounds varying in luminance. In this paper, the applicability of CAM18sl to situations different from the one for which it was originally developed is explored. The brightness perception predicted by this model (expressed in "bright") is compared with the outcome of the CIE Unified Glare Rating (UGR) for luminaires, the limiting luminance values for Variable Message Signs as indicated in the European standard for outdoor situations, the visual gloss (VG) formula to characterize the gloss of objects, the CIE grey-scale calculation for self-luminous devices, and the predicted brightness value of illuminated objects according to CIECAM02. Although the application domains mentioned above are very distinct, it appears that the predicted brightness perception of the CAM18sl model correlates well with the outcome of the particular and dedicated metrics. It seems that, for brightness perception, CAM18sl can be considered as a general model applicable for a wide range of applications. This could lead to a reduction of a number of application-specific metrics.
ABSTRACT
A model for brightness and hue perception of self-luminous stimuli surrounded by a self-luminous achromatic background has been developed based on a series of visual experiments. In the model, only the absolute spectral radiance values of the stimulus and background are used as input. Normalized cone excitations are calculated using the 10° Commission Internationale de l'Éclairage (CIE) 2006 cone fundamentals. A von Kries chromatic adaptation transform applied in the CIE 2006 cone space is adopted, and luminance compression and adaptation due to the self-luminous background are included by using a Michaelis-Menten function. Model parameters are determined by fitting the model to the experimental visual data obtained for brightness, hue, and the amount of color versus neutral. The model is validated with additional experimental data. An absolute brightness scale expressed in "bright" is proposed.