Ricco's Law

Ricco's Law explains the visual relationship between a target area and target contrast required for detection. It is shown below

$$log (Contrast) = K - log(Area) $$

Ricco's Law is applicable for regions where the target being detected is unresolved. This region is variable based on the amount of background luminance. Ricco's Law is based on the fact that the 'Signal' of the target being detected is proportional to the threshold contrast multiplied by the area. Therefore, the contrast threshold required for detection is proportional to the signal to noise ratio multiplied by the noise divided by the area. This leads to the above equation.