published June 30, 2020

My explanation of the vein illusion

Akiyoshi Kitaoka
(College of Comprehensive Psychology, Ritsumeikan University, Osaka, Japan)

since June 30, 2020

Veins appear to be bluish, though the pixels are not. This phenomenon is a color illusion.

Vein images show unique histograms of RGB values, in which they lack high or low values.

This histogram resembles that of the color illusion based upon additive color change.

histogram equalization↓  ↑additive color change

The hypothesis of "histogram equalization" proposed by Shapiro et al. (2018) can explain this color illusion. We think that the mechasnim of histogram equalization contributes to color constancy.

Shapiro, A., Hedjar, L., Dixon, E., and Kitaoka, A. (2018). Kitaoka's tomato: Two simple explanations based on information in the stimulus. i-Perception, 9(1), January-February, 1-9. PDF (open access)

histogram equalization↓  ↑histogram compression

Histogram equalization transforms the color of veins to be bluish color of reality. I think that we perceive this bluish color for veins, though the pixels alone are not bluish.

histogram compression↓  ↑histogram equalization

Histogram compression is available to change any image to a color illusion image. The obtained color illusion image can be converted to the original one with histogram equalization. This observation supports my explanation of the vein illusion.

Akiyoshi's illusion pages