Exploring the applicability of the CAM18sl brightness prediction.

S Hermans,P Hanselaer,K A G Smet

doi:10.1364/oe.27.014423

Abstract

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.

Highlights

A color appearance model called CAM18sl has been developed for the evaluation of self-luminous stimuli surrounded by a self-luminous and uncorrelated background [1]
Cone excitations are calculated using the 10° CIE 2006 cone fundamentals [2] for young adults and the normalization constants have been chosen such that the cone excitations of spectral equal-energy white are identical and nominally equal to the CIE 1964 10° luminance value
The brightness scale of CAM18sl is expressed in “bright”, a unit corresponding to the apparent brightness of a 10° spectral equal-energy self-luminous stimulus having a CIE 1964 10° luminance of 100 cd/m2 and surrounded by a dark (0 cd/m2) background

Summary

Introduction

A color appearance model called CAM18sl has been developed for the evaluation of self-luminous stimuli surrounded by a self-luminous and uncorrelated background [1]. The brightness scale of CAM18sl is expressed in “bright”, a unit corresponding to the apparent brightness of a 10° spectral equal-energy self-luminous stimulus having a CIE 1964 10° luminance of 100 cd/m2 and surrounded by a dark (0 cd/m2) background. The applicability of the CAM18sl brightness prediction is explored for a variety of practical applications for which the model was not developed originally These applications are the prediction of glare of uniform luminaires, the prediction of visual gloss of flat objects, the definition of minimum luminance values for variable message road signs, grey scale calculations for self-luminous devices and the brightness of object colors. It should be noticed that the applicability of the CIE UGR formula for non-uniform and colored light sources is still under discussion and other discomfort glare formulas have been proposed [6,7,8,9]. If one considers the object itself and the neutral grey as stimulus and background respectively, not self-luminous, CAM18sl can be applied and the brightness correlate of both CIECAM02 and CAM18sl can be compared

CAM18sl

CIE unified glare rating versus CAM18sl

Visual Gloss

Conclusion