Advanced Perceptual Contrast Algorithm


The Advanced Perceptual Contrast Algorithm (APCA) is a new way to compute contrast based on modern research on color perception.

These models are specifically related to color appearance on self-illuminated RGB computer displays & devices and also for modeling accessible user needs, with a focus on readability.


The WCAG 2.x contrast methods are being replaced for WCAG 3.0 APCA. The APCA generates a lightness/darkness contrast value based on a minimum font size and color pair, which is perceptually based. Regardless of how light or dark the two colors are, a contrast value of Lc 60 represents the same perceived readability contrast.


APCA is a part of the larger S-Luv Accessible Color Appearance Model known as SACAM (formerly SAPC).