Color handling

Author(s): Per Cederberg.

This module handles colors for usage in web pages, using the special web color format (with hexadecimal digits). The colors are handled as atoms, but are internally converted into numeric RGB representations.

• Usage and interface (color)
• Documentation on exports (color)

Usage and interface (color)

Documentation on exports (color)

PREDICATE: color2rgb/2:

Usage 1: color2rgb(WebColor,RGBColor)

• Description: Converts a WebColor (HTML hex coded color) to a RGBColor. The RGBColor is a term 'rgb(Red,Green,Blue)' where the color values should not be greater than 255 or less than 0.
• Should hold at call time: WebColor is an atom. (atm/1) RGBColor is a free variable. (var/1)
• Should hold upon exit: RGBColor is any term. (term/1)

Usage 2: color2rgb(WebColor,RGBColor)

• Description: Converts a RGBColor to a WebColor (HTML hex coded color). The RGBColor is a term 'rgb(Red,Green,Blue)' where the color values should not be greater than 255 or less than 0.
• Should hold at call time: WebColor is a free variable. (var/1) RGBColor is any term. (term/1)
• Should hold upon exit: WebColor is an atom. (atm/1)

PREDICATE: color2gray/2:

Usage: color2gray(Color,Gray)

• Description: Converts Color into a Gray, using different weights for each one of the color components.
• Should hold at call time: Color is an atom. (atm/1)
• Should hold upon exit: Gray is an atom. (atm/1)

PREDICATE: color2bw/2:

Usage: color2bw(Color,BlackOrWhite)

• Description: Calculates the BlackOrWhite (black or white representation) of a Color. The predicate uses the same intensity weighting as color2gray/2.
• Should hold at call time: Color is an atom. (atm/1)
• Should hold upon exit: BlackOrWhite is an atom. (atm/1)

PREDICATE: color_contrast/2:

Usage: color_contrast(Color1,Color2)

• Description: Controls that the Color1 and Color2 will have good contrast, i.e. that their color components differ sufficiently according to a weighted difference. If they don't, the predicate fails.
• Should hold at call time: Color1 is an atom. (atm/1) Color2 is an atom. (atm/1)

PREDICATE: color_bw_contrast/2:

Usage: color_bw_contrast(Color1,Color2)

• Description: Controls that the Color1 and Color2 will render to different colors on a black and white device. If the two colors will render to the same black or white representation, the predicate fails.
• Should hold at call time: Color1 is an atom. (atm/1) Color2 is an atom. (atm/1)

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