Perception of transparency in man and machine

The different tactics employed by human and machine vision systems in judging transparency are compared. Instead of luminance or reflectance (relative luminance), the human visual system uses lightness, a nonlinear function of reflectance, to estimate transparency. The representation of intensity information in terms of lightness restricts the operations that can be applied, and does not permit solving the equations describing the occurrence of transparency. Instead, the human visual system uses algorithms based on simple order and magnitude relations. One consequence of the human visual system not using a mathematically correct procedure is the occurrence of nonveridical perceptions of transparency. A second consequence is that the human visual system is not able to make accurate judgments of the degree of transparency. Figural cues are also important in the human perception of transparency. The tendency for the human visual system to see a simple organization leads to the perception of transparency even when the intensity pattern indicates transparency to be physically impossible. In contrast, given the luminances or reflectances, a machine vision system can apply the relevant equations for additive and subtractive color mixture to give veridical and quantitatively correct judgments of transparency.