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Articulation: brightness, apparent illumination, and contrast ratios
James A Schirillo1, Steven K Shevell
1Department of Psychology, Wake Forest University, Winston-Salem, NC 27109, USA. schirija@wfu.edu
Perception
|April 2, 2002
Summary
Visual perception of brightness is influenced by luminance edges. A constant contrast ratio along an edge signals different illumination levels, affecting perceived surface brightness systematically.
Area of Science:
- Visual perception
- Computational vision
- Color science
Background:
- Luminance edges in natural scenes arise from variations in surface reflectance or illumination.
- Distinguishing between reflectance and illumination is crucial for accurate visual interpretation.
Purpose of the Study:
- To investigate how the spatial organization of surfaces influences perceived brightness.
- To determine if a constant contrast-ratio luminance edge can segment scenes into different illumination regions.
Main Methods:
- Three experiments were conducted using 10 simulated achromatic surfaces.
- Spatial arrangements were manipulated to create luminance edges with and without a constant contrast-ratio.
- Perceived brightness of surface patches was compared across these arrangements.
Main Results:
- When a luminance edge with a constant contrast-ratio was present, perceived brightness systematically changed.
- These changes were compared to arrangements lacking this specific luminance edge criterion.
- Surfaces appeared brighter under higher perceived illumination, consistent with scene segmentation.
Conclusions:
- A luminance edge with a constant contrast-ratio acts as a cue for scene segmentation into illumination regions.
- This segmentation influences perceived surface brightness, mimicking real physical illumination differences.
- The visual system interprets constant contrast-ratio edges as indicative of illumination changes, impacting brightness perception.