Lightness, brightness, and brightness contrast: 1. Illuminance variation

Area of Science:

• Visual perception
• Color science
• Psychophysics

Background:

• Disk-and-annulus patterns present ambiguous luminance changes, conflating reflectance and illuminance.
• Complex patterns can disambiguate apparent reflectance perception.
• Previous research has not fully explored how different perceptual matching criteria affect reflectance estimation.

Purpose of the Study:

• To investigate how different perceptual matching criteria (brightness, lightness, brightness contrast) influence the estimation of surface reflectance.
• To determine if complex surrounds can lead to illumination-invariant reflectance matches.
• To quantify discrepancies between perceived lightness and actual reflectance.

Main Methods:

• Subjects performed matches on test and standard patches presented with varying surrounds in complex patterns.
• Matching criteria included apparent brightness, apparent lightness (reflectance), and brightness contrast.
• Stimuli varied in luminance and were presented under different illuminations.

Main Results:

• Brightness contrast matches were achieved when the test and standard patch/surround luminance ratios were equal.
• Lightness matches were illumination-invariant but introduced a small, constant error, particularly for decrements (approx. 1.5 Munsell value steps).
• Brightness matches showed significant covariation with illuminance levels.

Conclusions:

• Perceptual matching of reflectance is criterion-dependent, with brightness contrast offering the most accurate estimation.
• While lightness matches reduce illuminance dependency, they are not perfect reflectance matches due to surround effects.
• Brightness perception is strongly influenced by illuminance, limiting its use for reflectance estimation.