Contrast
Luminance Contrast
Michelson Contrast
Modulation
Peak-to-Peak Contrast
Weber Contrast

(Terms of photometry/physiology)

Contrast (Luminance Contrast) is the relationship between the luminance of a brighter area of interest and that of an adjacent darker area.

Mathematically, the difference between the two luminances divided by the lower luminance . This definition is also called Weber Contrast, and is the most commonly useful one in the context of lighting.

C = (L_max - L_min) / L_min
 

Simple Contrast values are often used in photography, to specify the difference between bright and dark parts of the picture. This definition is not useful for real-world luminances, because of their much higher dynamic range and the logarithmic .

C_simple = L_max / L_min
 

Peak-to-Peak Constrast (Michelson Contrast, Modulation) measures the relation between the spread and the sum of the two luminances. This definition is typically used in signal processing theory, to determine the quality of a signal relative to its noise level. In the context of vision, such noise could be caused by scattered light introduced into the view path by a translucent element partly obscuring the scene behind it.

Modulation = (L_max - L_min) / (L_max + L_min)