Stiles' threshold-versus-intensity (t.v.i.) template curve

Data key


  1. Log relative background intensity, log(x)
  2. Log relative increment threshold, log[ζ(x)]


From Table A of Stiles (1978). See also Table 1(7.4.3) of Wyszecki & Stiles (1982).

For log x > 0.5, log[ζ(x)] = -0.94 - log(x).

This function defines the average shape of the t.v.i. curve of an individual foveal color (or π) mechanism.


Stiles, W. S. (1978). Mechanisms of Colour Vision. London: Academic.

Wyszecki, G., & Stiles, W. S. (1982). Color Science: concepts and methods, quantitative data and formulae. (2nd ed.). New York: Wiley.