112 Color and Luminance Constancy

There are three main aspects of vision that allow the consistent perception of color in objects independent of illumination:

1. Chromatic adaptation: when the light source contains a disproportionate amount of light in one section of the spectrum, the responses of the relevant photoreceptors are suppressed, shifting our perception away from the dominant wavelength.
2. Local context: we compare all the colors in a scene to normalize our perception. This process takes place at a conscious and unconscious level.
3. Prior knowledge: certain objects characterized by a distinct color will be perceived as this color despite differential illumination.

Light vs Color Constancy

• Light constancy and color constancy are both perceptual phenomena related to how humans perceive objects under varying lighting conditions however, they refer to different aspects of perception

Light Constancy

• Lightness is the subjective perception of the range between black and white. Surface lightness is one of the fundamental characteristics of an item, alongside its size and motion. However, our comprehension of the brain’s process for calculating lightness is still lacking. The issue lies in the fact that the perception of an object’s shade of gray is not accurately determined by the amount of light reflected by its surface (reflectance) and the intensity of the lighting. However, the perception of lightness on a surface tends to stay the same even when the lighting conditions vary, this effect is known as lightness constancy.

Color Constancy

• Color constancy refers to the extent to which surface color is consistently perceived, allowing humans to recognize things based on their color even when the lighting conditions vary. Nevertheless, the precise processes that support the stability of the color vision system remain not fully understood.
• The cone excitations of an illuminated surface are influenced by both the spectral composition of the illuminant and the spectral reflectance of the surface. Therefore, when the illuminant of a scene changes, the cone signals associated with it also change. Nevertheless, many experiments on human perception of colored surfaces demonstrate a significant degree of perceptual consistency, wherein the visual appearance of the surface remains very stable.

Testing light constancy: The link below is to a page where they do three psychophysical studies to test our optimal color theory, which says that we absorb the physical color gamut under different lighting conditions and use the prior to guess the lighting color https://jov.arvojournals.org/article.aspx?articleid=2772352#247172943

To learn more, take a look at this video about color and light constancy with great examples!