The Role of Low-Spatial Frequency Components in "High Vision" Experiments

Recent discussions about mechanisms for modeling human lightness have centered on whether these mechanisms are the result of “Early Vision”, implying that lightness is calculated before depth is undertaken, or “Mid Vision”, implying the simultaneous solutions of both depth and lightness, or “High Vision” mechanisms that imply depth information is used to estimate lightness. This paper begins by reviewing a series of lightness experiments used as evidence for “High Vision”. In particular, it analyzes the influence of both Simultaneous Contrast and low-spatial frequency components on apparent lightness. Further, this paper investigates a variety of “Diamond Wall” lightness experiments. It argues that further study of the “Diamonds” experiments demonstrates an “EarlyVision” explanation, without reliance on illumination, transparency, apparent depth or junctions. Grays ordinarily look darker on light backgrounds. Two rows of diamonds looked the same on different backgrounds, when the diamond tips crossed into the other background. The addition of different gray tips, consistent with illumination changes, released the rest of the diamonds to no longer match. Grays on light backgrounds reverted to looking darker. Additional experiments show that the introduction of any edge along the light-dark background boundary releases the diamonds to look different in different surrounds. These experiments are arguments for “Early-Vision” lightness mechanisms because simultaneous contrast and low-spatial frequency sampling can account for lightness without the need for high-level mental processes.