Class Color::Palette::MonoContrast
In: lib/color/palette/monocontrast.rb
Parent: Object
Enumerable Gimp CMYK\n[lib/color.rb\nlib/color/cmyk.rb] GrayScale\n[lib/color.rb\nlib/color/grayscale.rb] RGB\n[lib/color.rb\nlib/color/rgb-colors.rb\nlib/color/rgb.rb] YIQ\n[lib/color.rb\nlib/color/yiq.rb] HSL MonoContrast lib/color/cmyk.rb lib/color/grayscale.rb lib/color/rgb.rb lib/color/yiq.rb lib/color/hsl.rb CSS lib/color/palette/gimp.rb lib/color/palette/monocontrast.rb Palette Color dot/m_9_0.png

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.

Methods

Constants

DEFAULT_MINIMUM_BRIGHTNESS_DIFF = (125.0 / 255.0)
DEFAULT_MINIMUM_COLOR_DIFF = (500.0 / 255.0)

Attributes

background  [R]  Hash of CSS background colour values.

This is always 11 values:

0:The starting colour.
+1..+5:Lighter colours.
-1..-5:Darker colours.
foreground  [R]  Hash of CSS foreground colour values.

This is always 11 values:

0:The starting colour.
+1..+5:Lighter colours.
-1..-5:Darker colours.
minimum_brightness_diff  [RW]  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.
minimum_color_diff  [RW]  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.

[Source]

    # File lib/color/palette/monocontrast.rb, line 88
88:   def initialize(background, foreground = nil)
89:     @minimum_brightness_diff = DEFAULT_MINIMUM_BRIGHTNESS_DIFF
90:     @minimum_color_diff = DEFAULT_MINIMUM_COLOR_DIFF
91: 
92:     regenerate(background, foreground)
93:   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.

[Source]

     # File lib/color/palette/monocontrast.rb, line 166
166:   def brightness_diff(c1, c2)
167:     (c1.brightness - c2.brightness).abs
168:   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.

[Source]

     # File lib/color/palette/monocontrast.rb, line 134
134:   def calculate_foreground(background, foreground)
135:     nfg = nil
136:       # Loop through brighter and darker versions of the foreground color.
137:       # The numbers here represent the amount of foreground color to mix
138:       # with black and white.
139:     [100, 75, 50, 25, 0].each do |percent|
140:       dfg = foreground.darken_by(percent)
141:       lfg = foreground.lighten_by(percent)
142: 
143:       dbd = brightness_diff(background, dfg)
144:       lbd = brightness_diff(background, lfg)
145: 
146:       if lbd > dbd
147:         nfg = lfg
148:         nbd = lbd
149:       else
150:         nfg = dfg
151:         nbd = dbd
152:       end
153: 
154:       ncd = color_diff(background, nfg)
155: 
156:       break if nbd >= @minimum_brightness_diff and ncd >= @minimum_color_diff
157:     end
158:     nfg
159:   end

Returns the contrast between to colours, a decimal value between 0 and

  1. W3C accessibility guidelines for colour

contrast suggest that this value be at least approximately 1.96 (500 / 255.0) for proper contrast.

[Source]

     # File lib/color/palette/monocontrast.rb, line 174
174:   def color_diff(c1, c2)
175:     r = (c1.r - c2.r).abs
176:     g = (c1.g - c2.g).abs
177:     b = (c1.b - c2.b).abs
178:     r + g + b
179:   end

[Source]

    # File lib/color/palette/monocontrast.rb, line 74
74:   def minimum_color_diff=(cd) #:noco:
75:     if cd.nil?
76:       @minimum_color_diff = DEFAULT_MINIMUM_COLOR_DIFF
77:     elsif cd > 3.0
78:       @minimum_color_diff = 3.0
79:     elsif cd < 0.0
80:       @minimum_color_diff = 0.0
81:     else
82:       @minimum_color_diff = cd
83:     end
84:     regenerate(@background[0], @foreground[0])
85:   end

Generate the colour palettes.

[Source]

     # File lib/color/palette/monocontrast.rb, line 96
 96:   def regenerate(background, foreground = nil)
 97:     foreground ||= background
 98:     background = background.to_rgb
 99:     foreground = foreground.to_rgb
100: 
101:     @background = {}
102:     @foreground = {}
103: 
104:     @background[-5] = background.darken_by(10)
105:     @background[-4] = background.darken_by(25)
106:     @background[-3] = background.darken_by(50)
107:     @background[-2] = background.darken_by(75)
108:     @background[-1] = background.darken_by(85)
109:     @background[ 0] = background
110:     @background[+1] = background.lighten_by(85)
111:     @background[+2] = background.lighten_by(75)
112:     @background[+3] = background.lighten_by(50)
113:     @background[+4] = background.lighten_by(25)
114:     @background[+5] = background.lighten_by(10)
115: 
116:     @foreground[-5] = calculate_foreground(@background[-5], foreground)
117:     @foreground[-4] = calculate_foreground(@background[-4], foreground)
118:     @foreground[-3] = calculate_foreground(@background[-3], foreground)
119:     @foreground[-2] = calculate_foreground(@background[-2], foreground)
120:     @foreground[-1] = calculate_foreground(@background[-1], foreground)
121:     @foreground[ 0] = calculate_foreground(@background[ 0], foreground)
122:     @foreground[+1] = calculate_foreground(@background[+1], foreground)
123:     @foreground[+2] = calculate_foreground(@background[+2], foreground)
124:     @foreground[+3] = calculate_foreground(@background[+3], foreground)
125:     @foreground[+4] = calculate_foreground(@background[+4], foreground)
126:     @foreground[+5] = calculate_foreground(@background[+5], foreground)
127:   end

[Validate]