Delahunt Peter B, Brainard David H
Department of Ophthalmology and Section of Neurobiology, Physiology and Behavior, University of California Davis, CA, USA.
J Vis. 2004 Feb 18;4(2):57-81. doi: 10.1167/4.2.1.
The chromaticities of natural daylights cluster around the blackbody locus. We investigated whether the mechanisms that mediate human color constancy embody this statistical regularity of the natural environment, so that constancy is best when the illuminant change is one likely to occur. Observers viewed scenes displayed on a CRT-based stereoscope and adjusted a test patch embedded in the scene until it appeared achromatic. Scenes were rendered using physics-based graphics software (RADIANCE) coupled with custom extensions that ensured colorimetric accuracy. Across conditions, both the simulated illuminant and the simulated reflectance of scene objects were varied. Achromatic settings from paired conditions were used to compute a constancy index (CI) that characterizes the stability of object appearance across the two illuminants of the pair. Constancy indices were measured for four illuminant changes from a Neutral illuminant (CIE D65). Two of these changes (Blue and Yellow) were consistent with the statistics of daylight, whereas two (Green and Red) were not. The results indicate that constancy was least across the Red change, as one would expect for the statistics of natural daylight. Constancy for the Green direction, however, exceeded that for the Yellow illuminant change and was comparable to that for the Blue. This result is difficult to reconcile with the hypothesis that mechanisms of human constancy incorporate the statistics of daylights. Some possible reasons for the discrepancy are discussed.
自然日光的色度聚集在黑体轨迹周围。我们研究了介导人类颜色恒常性的机制是否体现了自然环境的这种统计规律，以便当光源变化是可能发生的情况时，恒常性最佳。观察者观看基于阴极射线管的立体镜上显示的场景，并调整嵌入场景中的测试色块，直到它看起来是无色的。使用基于物理的图形软件（RADIANCE）以及确保比色准确性的自定义扩展来渲染场景。在各种条件下，模拟光源和场景物体的模拟反射率都会变化。配对条件下的无色设置用于计算一个恒常性指数（CI），该指数表征了物体外观在该对的两个光源之间的稳定性。测量了从中性光源（CIE D65）进行的四种光源变化的恒常性指数。其中两种变化（蓝色和黄色）与日光统计数据一致，而另外两种（绿色和红色）则不一致。结果表明，正如自然日光统计数据所预期的那样，红色变化时的恒常性最低。然而，绿色方向的恒常性超过了黄色光源变化时的恒常性，并且与蓝色变化时的恒常性相当。这一结果难以与人类恒常性机制纳入日光统计数据的假设相协调。讨论了差异的一些可能原因。
