The inevitably uncertain meaning of luminance in visual stimuli (the inverse optics problem).

<p>Retinal luminance values are determined by combinations of illumination and reflectance, as well as a variety of other factors (e.g., atmospheric transmittance, spectral content, occlusion, object distance, etc.). These physical determinants of retinal luminance values are conflated in visual stimuli and cannot be disentangled by any algorithmic process (adapted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060490#pone.0060490-Yang1" target="_blank">[20]</a>, pp.22).