class Color::Palette::MonoContrast
Generates a monochromatic constrasting colour palette for background and foreground. What does this mean?
Monochromatic: A single colour is used to generate the base palette, and this colour is lightened five times and darkened five times to provide eleven distinct colours.
Contrasting: The foreground is also generated as a monochromatic colour palettte; however, all generated colours are tested to see that they are appropriately contrasting to ensure maximum readability of the foreground against the background.
Constants
- DEFAULT_MINIMUM_BRIGHTNESS_DIFF
- DEFAULT_MINIMUM_COLOR_DIFF
Attributes
Hash of CSS background colour values.
This is always 11 values:
- 0
-
The starting colour.
- +1..+5
-
Lighter colours.
- -1..-5
-
Darker colours.
Hash of CSS foreground colour values.
This is always 11 values:
- 0
-
The starting colour.
- +1..+5
-
Lighter colours.
- -1..-5
-
Darker colours.
The minimum brightness difference between the background and the
foreground, and must be between 0..1. Setting this value will regenerate
the palette based on the base colours. The default value for this is 125 /
255.0. If this value is set to nil
, it will be restored to the
default.
The minimum colour difference between the background and the foreground, and must be between 0..3. Setting this value will regenerate the palette based on the base colours. The default value for this is 500 / 255.0.
Public Class Methods
Generate the initial palette.
# File lib/color/palette/monocontrast.rb, line 88 def initialize(background, foreground = nil) @minimum_brightness_diff = DEFAULT_MINIMUM_BRIGHTNESS_DIFF @minimum_color_diff = DEFAULT_MINIMUM_COLOR_DIFF regenerate(background, foreground) end
Public Instance Methods
Returns the absolute difference between the brightness levels of two colours. This will be a decimal value between 0 and 1. W3C accessibility guidelines for colour contrast suggest that this value be at least approximately 0.49 (125 / 255.0) for proper contrast.
# File lib/color/palette/monocontrast.rb, line 166 def brightness_diff(c1, c2) (c1.brightness - c2.brightness).abs end
Given a background colour and a foreground colour, modifies the foreground colour so that it will have enough contrast to be seen against the background colour.
Uses mininum_brightness_diff and minimum_color_diff.
# File lib/color/palette/monocontrast.rb, line 134 def calculate_foreground(background, foreground) nfg = nil # Loop through brighter and darker versions of the foreground color. # The numbers here represent the amount of foreground color to mix # with black and white. [100, 75, 50, 25, 0].each do |percent| dfg = foreground.darken_by(percent) lfg = foreground.lighten_by(percent) dbd = brightness_diff(background, dfg) lbd = brightness_diff(background, lfg) if lbd > dbd nfg = lfg nbd = lbd else nfg = dfg nbd = dbd end ncd = color_diff(background, nfg) break if nbd >= @minimum_brightness_diff and ncd >= @minimum_color_diff end nfg end
Returns the contrast between to colours, a decimal value between 0 and
-
W3C accessibility guidelines for colour
contrast suggest that this value be at least approximately 1.96 (500 / 255.0) for proper contrast.
# File lib/color/palette/monocontrast.rb, line 174 def color_diff(c1, c2) r = (c1.r - c2.r).abs g = (c1.g - c2.g).abs b = (c1.b - c2.b).abs r + g + b end
# File lib/color/palette/monocontrast.rb, line 74 def minimum_color_diff=(cd) #:noco: if cd.nil? @minimum_color_diff = DEFAULT_MINIMUM_COLOR_DIFF elsif cd > 3.0 @minimum_color_diff = 3.0 elsif cd < 0.0 @minimum_color_diff = 0.0 else @minimum_color_diff = cd end regenerate(@background[0], @foreground[0]) end
Generate the colour palettes.
# File lib/color/palette/monocontrast.rb, line 96 def regenerate(background, foreground = nil) foreground ||= background background = background.to_rgb foreground = foreground.to_rgb @background = {} @foreground = {} @background[-5] = background.darken_by(10) @background[-4] = background.darken_by(25) @background[-3] = background.darken_by(50) @background[-2] = background.darken_by(75) @background[-1] = background.darken_by(85) @background[ 0] = background @background[+1] = background.lighten_by(85) @background[+2] = background.lighten_by(75) @background[+3] = background.lighten_by(50) @background[+4] = background.lighten_by(25) @background[+5] = background.lighten_by(10) @foreground[-5] = calculate_foreground(@background[-5], foreground) @foreground[-4] = calculate_foreground(@background[-4], foreground) @foreground[-3] = calculate_foreground(@background[-3], foreground) @foreground[-2] = calculate_foreground(@background[-2], foreground) @foreground[-1] = calculate_foreground(@background[-1], foreground) @foreground[ 0] = calculate_foreground(@background[ 0], foreground) @foreground[+1] = calculate_foreground(@background[+1], foreground) @foreground[+2] = calculate_foreground(@background[+2], foreground) @foreground[+3] = calculate_foreground(@background[+3], foreground) @foreground[+4] = calculate_foreground(@background[+4], foreground) @foreground[+5] = calculate_foreground(@background[+5], foreground) end