Contrast threshold function

Contrast sensitivity is the ability to discern between luminosities of different levels in a static image. Contrast sensitivity varies between individuals, maxing out at approximately 20 years of age, and at spatial frequencies of about 2-5 cycles/degree.

The contrast threshold function (CSF), also called the modular transfer function is derived from a graph plotting the relationship between the horizontal axis of spatial frequencies of simple figures (eg a grating, with different sized gaps between the bars) and the vertical axis of a subjects sensitivity to perceiving the fluctuations in luminance across the images.

This is thus the reciprocal of the absolute threshold.