Parent

Namespace

Color::RGB

An RGB colour object.

Public Class Methods

from_fraction(r = 0.0, g = 0.0, b = 0.0) click to toggle source

Creates an RGB colour object from fractional values 0..1.

Color::RGB.from_fraction(.3, .2, .1)
# File lib/color/rgb.rb, line 30
def from_fraction(r = 0.0, g = 0.0, b = 0.0)
  colour = Color::RGB.new
  colour.r = r
  colour.g = g
  colour.b = b
  colour
end
from_html(html_colour) click to toggle source

Creates an RGB colour object from an HTML colour descriptor (e.g., "fed" or "#cabbed;".

Color::RGB.from_html("fed")
Color::RGB.from_html("#fed")
Color::RGB.from_html("#cabbed")
Color::RGB.from_html("cabbed")
# File lib/color/rgb.rb, line 45
def from_html(html_colour)
  html_colour = html_colour.gsub(%{[#;]}, '')
  case html_colour.size 
  when 3
    colours = html_colour.scan(%{[0-9A-Fa-f]}).map { |el| (el * 2).to_i(16) }
  when 6
    colours = html_colour.scan(%<[0-9A-Fa-f]{2}>).map { |el| el.to_i(16) }
  else
    raise ArgumentError
  end

  Color::RGB.new(*colours)
end
from_percentage(r = 0, g = 0, b = 0) click to toggle source

Creates an RGB colour object from percentages 0..100.

Color::RGB.from_percentage(10, 20 30)
# File lib/color/rgb.rb, line 23
def from_percentage(r = 0, g = 0, b = 0)
  from_fraction(r / 100.0, g / 100.0, b / 100.0)
end
new(r = 0, g = 0, b = 0) click to toggle source

Creates an RGB colour object from the standard range 0..255.

Color::RGB.new(32, 64, 128)
Color::RGB.new(0x20, 0x40, 0x80)
# File lib/color/rgb.rb, line 79
def initialize(r = 0, g = 0, b = 0)
  @r = r / 255.0
  @g = g / 255.0
  @b = b / 255.0
end

Public Instance Methods

==(other) click to toggle source

Compares the other colour to this one. The other colour will be converted to RGB before comparison, so the comparison between a RGB colour and a non-RGB colour will be approximate and based on the other colour's default to_rgb conversion. If there is no to_rgb conversion, this will raise an exception. This will report that two RGB colours are equivalent if all component values are within 1e-4 (0.0001) of each other.

# File lib/color/rgb.rb, line 67
def ==(other)
  other = other.to_rgb
  other.kind_of?(Color::RGB) and
  ((@r - other.r).abs <= 1e-4) and
  ((@g - other.g).abs <= 1e-4) and
  ((@b - other.b).abs <= 1e-4)
end
adjust_brightness(percent) click to toggle source

Returns a new colour with the brightness adjusted by the specified percentage. Negative percentages will darken the colour; positive percentages will brighten the colour.

Color::RGB::DarkBlue.adjust_brightness(10)
Color::RGB::DarkBlue.adjust_brightness(-10)
# File lib/color/rgb.rb, line 247
def adjust_brightness(percent)
  percent /= 100.0
  percent += 1.0
  percent  = [ percent, 2.0 ].min
  percent  = [ 0.0, percent ].max

  hsl      = to_hsl
  hsl.l   *= percent
  hsl.to_rgb
end
adjust_hue(percent) click to toggle source

Returns a new colour with the hue adjusted by the specified percentage. Negative percentages will reduce the hue; positive percentages will increase the hue.

Color::RGB::DarkBlue.adjust_hue(10)
Color::RGB::DarkBlue.adjust_hue(-10)
# File lib/color/rgb.rb, line 281
def adjust_hue(percent)
  percent  /= 100.0
  percent  += 1.0
  percent  = [ percent, 2.0 ].min
  percent  = [ 0.0, percent ].max

  hsl      = to_hsl
  hsl.h   *= percent
  hsl.to_rgb
end
adjust_saturation(percent) click to toggle source

Returns a new colour with the saturation adjusted by the specified percentage. Negative percentages will reduce the saturation; positive percentages will increase the saturation.

Color::RGB::DarkBlue.adjust_saturation(10)
Color::RGB::DarkBlue.adjust_saturation(-10)
# File lib/color/rgb.rb, line 264
def adjust_saturation(percent)
  percent  /= 100.0
  percent  += 1.0
  percent  = [ percent, 2.0 ].min
  percent  = [ 0.0, percent ].max

  hsl      = to_hsl
  hsl.s   *= percent
  hsl.to_rgb
end
brightness() click to toggle source

Returns the brightness value for a colour, a number between 0..1. Based on the Y value of YIQ encoding, representing luminosity, or perceived brightness.

This may be modified in a future version of color-tools to use the luminosity value of HSL.

# File lib/color/rgb.rb, line 232
def brightness
  to_yiq.y
end
darken_by(percent) click to toggle source

Mix the RGB hue with Black so that the RGB hue is the specified percentage of the resulting colour. Strictly speaking, this isn't a darken_by operation.

# File lib/color/rgb.rb, line 209
def darken_by(percent)
  mix_with(Black, percent)
end
html() click to toggle source

Present the colour as an HTML/CSS colour string.

# File lib/color/rgb.rb, line 98
def html
  r = (@r * 255).round
  r = 255 if r > 255

  g = (@g * 255).round
  g = 255 if g > 255

  b = (@b * 255).round
  b = 255 if b > 255

  "#%02x%02x%02x" % [ r, g, b ]
end
lighten_by(percent) click to toggle source

Mix the RGB hue with White so that the RGB hue is the specified percentage of the resulting colour. Strictly speaking, this isn't a darken_by operation.

# File lib/color/rgb.rb, line 202
def lighten_by(percent)
  mix_with(White, percent)
end
mix_with(mask, opacity) click to toggle source

Mix the mask colour (which must be an RGB object) with the current colour at the stated opacity percentage (0..100).

# File lib/color/rgb.rb, line 215
def mix_with(mask, opacity)
  opacity /= 100.0
  rgb = self.dup
  
  rgb.r = (@r * opacity) + (mask.r * (1 - opacity))
  rgb.g = (@g * opacity) + (mask.g * (1 - opacity))
  rgb.b = (@b * opacity) + (mask.b * (1 - opacity))

  rgb
end
pdf_fill() click to toggle source

Present the colour as a DeviceRGB fill colour string for PDF. This will be removed from the default package in color-tools 2.0.

# File lib/color/rgb.rb, line 87
def pdf_fill
  PDF_FORMAT_STR % [ @r, @g, @b, "rg" ]
end
pdf_stroke() click to toggle source

Present the colour as a DeviceRGB stroke colour string for PDF. This will be removed from the default package in color-tools 2.0.

# File lib/color/rgb.rb, line 93
def pdf_stroke
  PDF_FORMAT_STR % [ @r, @g, @b, "RG" ]
end
to_cmyk() click to toggle source

Converts the RGB colour to CMYK. Most colour experts strongly suggest that this is not a good idea (some even suggesting that it's a very bad idea). CMYK represents additive percentages of inks on white paper, whereas RGB represents mixed colour intensities on a black screen.

However, the colour conversion can be done. The basic method is multi-step:

  1. Convert the R, G, and B components to C, M, and Y components.

    c = 1.0 – r
    m = 1.0 – g
    y = 1.0 – b
  2. Compute the minimum amount of black (K) required to smooth the colour in inks.

    k = min(c, m, y)
  3. Perform undercolour removal on the C, M, and Y components of the colours because less of each colour is needed for each bit of black. Also, regenerate the black (K) based on the undercolour removal so that the colour is more accurately represented in ink.

    c = min(1.0, max(0.0, c – UCR(k)))
    m = min(1.0, max(0.0, m – UCR(k)))
    y = min(1.0, max(0.0, y – UCR(k)))
    k = min(1.0, max(0.0, BG(k)))

The undercolour removal function and the black generation functions return a value based on the brightness of the RGB colour.

# File lib/color/rgb.rb, line 138
def to_cmyk
  c = 1.0 - @r.to_f
  m = 1.0 - @g.to_f
  y = 1.0 - @b.to_f

  k = [c, m, y].min
  k = k - (k * brightness)

  c = [1.0, [0.0, c - k].max].min
  m = [1.0, [0.0, m - k].max].min
  y = [1.0, [0.0, y - k].max].min
  k = [1.0, [0.0, k].max].min

  Color::CMYK.from_fraction(c, m, y, k)
end
to_grayscale() click to toggle source
# File lib/color/rgb.rb, line 235
def to_grayscale
  Color::GrayScale.from_fraction(to_hsl.l)
end
Also aliased as: to_greyscale
to_greyscale() click to toggle source
Alias for: to_grayscale
to_hsl() click to toggle source

Returns the HSL colour encoding of the RGB value.

# File lib/color/rgb.rb, line 167
def to_hsl
  min   = [ @r, @g, @b ].min
  max   = [ @r, @g, @b ].max
  delta = (max - min).to_f

  lum   = (max + min) / 2.0

  if delta <= 1e-5  # close to 0.0, so it's a grey
    hue = 0
    sat = 0
  else
    if (lum - 0.5) <= 1e-5
      sat = delta / (max + min).to_f
    else
      sat = delta / (2 - max - min).to_f
    end

    if @r == max
      hue = (@g - @b) / delta.to_f
    elsif @g == max
      hue = (2.0 + @b - @r) / delta.to_f
    elsif (@b - max) <= 1e-5
      hue = (4.0 + @r - @g) / delta.to_f
    end
    hue /= 6.0

    hue += 1 if hue < 0
    hue -= 1 if hue > 1
  end
  Color::HSL.from_fraction(hue, sat, lum)
end
to_rgb(ignored = nil) click to toggle source
# File lib/color/rgb.rb, line 154
def to_rgb(ignored = nil)
  self
end
to_yiq() click to toggle source

Returns the YIQ (NTSC) colour encoding of the RGB value.

# File lib/color/rgb.rb, line 159
def to_yiq
  y = (@r * 0.299) + (@g *  0.587) + (@b *  0.114)
  i = (@r * 0.596) + (@g * -0.275) + (@b * -0.321)
  q = (@r * 0.212) + (@g * -0.523) + (@b *  0.311)
  Color::YIQ.from_fraction(y, i, q)
end

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