Calculates the contrast between two colors using the APCA (Accessible Perceptual Contrast Algorithm).
APCA is a modern contrast algorithm designed to replace WCAG 2.x contrast metrics.
It was developed by Andrew Somers to better predict perceived contrast for modern
displays and to address limitations in the WCAG 2.x contrast formula.
The algorithm uses different calculations based on the polarity (whether text is darker
or lighter than the background), applies non-linear transformations to account for human
perception, and includes special handling for very dark colors.
Key characteristics:
Produces values from approximately -108% to 106% (negative values indicate light text on dark background)
Accounts for the non-linear perception of contrast in human vision
Uses different calculations based on polarity (dark-on-light vs. light-on-dark)
Applies soft clamping to very dark colors to prevent excessive contrast
Designed specifically for predicting readability of text
Recommended minimum values vary by font size and weight:
Large, bold text: 45%
Normal body text: 60%
Small or thin text: 75%
Limitations:
More complex than simpler contrast metrics
Still evolving and may change in future versions
Not yet officially adopted in accessibility standards
Requires conversion to specific color spaces for accurate results
Calculates the contrast between two colors using the APCA (Accessible Perceptual Contrast Algorithm).
APCA is a modern contrast algorithm designed to replace WCAG 2.x contrast metrics. It was developed by Andrew Somers to better predict perceived contrast for modern displays and to address limitations in the WCAG 2.x contrast formula.
The algorithm uses different calculations based on the polarity (whether text is darker or lighter than the background), applies non-linear transformations to account for human perception, and includes special handling for very dark colors.
Key characteristics:
Limitations: