Class: Color::RGB

Inherits:
Object
  • Object
show all
Includes:
Color
Defined in:
lib/color/rgb.rb,
lib/color.rb,
lib/color/rgb/colors.rb,
lib/color/rgb/contrast.rb,
lib/color/rgb/metallic.rb

Overview

An RGB colour object.

Defined Under Namespace

Modules: Metallic

Constant Summary collapse

PDF_FORMAT_STR =

The format of a DeviceRGB colour for PDF. In color-tools 2.0 this will be removed from this package and added back as a modification by the PDF::Writer package.

"%.3f %.3f %.3f %s"

Constants included from Color

COLOR_EPSILON, COLOR_TOLERANCE, COLOR_VERSION, GreyScale

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Color

#==, coerce, const_missing, equivalent?, #name, #names, #names=, near?, near_one?, near_one_or_more?, near_zero?, near_zero_or_less?, new, normalize, normalize_byte, normalize_to_range, normalize_word

Constructor Details

#initialize(r = 0, g = 0, b = 0, radix = 255.0, &block) ⇒ RGB

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

Color::RGB.new(32, 64, 128)
Color::RGB.new(0x20, 0x40, 0x80)



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# File 'lib/color/rgb.rb', line 19

def initialize(r = 0, g = 0, b = 0, radix = 255.0, &block) # :yields self:
  @r, @g, @b = [ r, g, b ].map { |v| Color.normalize(v / radix) }
  block.call(self) if block
end

Class Method Details

.by_css(name_or_hex, &block) ⇒ Object

Return a colour as identified by the colour name, or by hex.



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# File 'lib/color/rgb.rb', line 648

def by_css(name_or_hex, &block)
  by_name(name_or_hex) { by_hex(name_or_hex, &block) }
end

.by_hex(hex, &block) ⇒ Object

Find or create a colour by an HTML hex code. This differs from the #from_html method in that if the colour code matches a named colour, the existing colour will be returned.

Color::RGB.by_hex('ff0000').name # => 'red'
Color::RGB.by_hex('ff0001').name # => nil

If a block is provided, the value that is returned by the block will be returned instead of the exception caused by an error in providing a correct hex format.



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# File 'lib/color/rgb.rb', line 632

def by_hex(hex, &block)
  __by_hex.fetch(html_hexify(hex)) { from_html(hex) }
rescue
  if block
    block.call
  else
    raise
  end
end

.by_name(name, &block) ⇒ Object

Return a colour as identified by the colour name.



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# File 'lib/color/rgb.rb', line 643

def by_name(name, &block)
  __by_name.fetch(name.to_s.downcase, &block)
end

.extract_colors(text, mode = :both) ⇒ Object

Extract named or hex colours from the provided text.



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# File 'lib/color/rgb.rb', line 653

def extract_colors(text, mode = :both)
  text  = text.downcase
  regex = case mode
          when :name
            Regexp.union(__by_name.keys)
          when :hex
            Regexp.union(__by_hex.keys)
          when :both
            Regexp.union(__by_hex.keys + __by_name.keys)
          end

  text.scan(regex).map { |match|
    case mode
    when :name
      by_name(match)
    when :hex
      by_hex(match)
    when :both
      by_css(match)
    end
  }
end

.from_fraction(r = 0.0, g = 0.0, b = 0.0, &block) ⇒ Object

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

Color::RGB.from_fraction(.3, .2, .1)



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# File 'lib/color/rgb.rb', line 592

def from_fraction(r = 0.0, g = 0.0, b = 0.0, &block)
  new(r, g, b, 1.0, &block)
end

.from_grayscale_fraction(l = 0.0, &block) ⇒ Object Also known as: from_greyscale_fraction

Creates an RGB colour object from a grayscale fractional value 0..1.



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# File 'lib/color/rgb.rb', line 597

def from_grayscale_fraction(l = 0.0, &block)
  new(l, l, l, 1.0, &block)
end

.from_html(html_colour, &block) ⇒ Object

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")



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# File 'lib/color/rgb.rb', line 609

def from_html(html_colour, &block)
  # When we can move to 1.9+ only, this will be \h
  h = html_colour.scan(/[0-9a-f]/i)
  case h.size
  when 3
    new(*h.map { |v| (v * 2).to_i(16) }, &block)
  when 6
    new(*h.each_slice(2).map { |v| v.join.to_i(16) }, &block)
  else
    raise ArgumentError, "Not a supported HTML colour type."
  end
end

.from_percentage(r = 0, g = 0, b = 0, &block) ⇒ Object

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

Color::RGB.from_percentage(10, 20, 30)



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# File 'lib/color/rgb.rb', line 585

def from_percentage(r = 0, g = 0, b = 0, &block)
  new(r, g, b, 100.0, &block)
end

Instance Method Details

#+(other) ⇒ Object

Adds another colour to the current colour. The other colour will be converted to RGB before addition. This conversion depends upon a #to_rgb method on the other colour.

The addition is done using the RGB Accessor methods to ensure a valid colour in the result.



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# File 'lib/color/rgb.rb', line 532

def +(other)
  self.class.from_fraction(r + other.r, g + other.g, b + other.b)
end

#-(other) ⇒ Object

Subtracts another colour to the current colour. The other colour will be converted to RGB before subtraction. This conversion depends upon a #to_rgb method on the other colour.

The subtraction is done using the RGB Accessor methods to ensure a valid colour in the result.



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# File 'lib/color/rgb.rb', line 542

def -(other)
  self + (-other)
end

#-@ ⇒ Object

Numerically negate the color. This results in a color that is only usable for subtraction.



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# File 'lib/color/rgb.rb', line 563

def -@
  rgb = self.dup
  rgb.instance_variable_set(:@r, -rgb.r)
  rgb.instance_variable_set(:@g, -rgb.g)
  rgb.instance_variable_set(:@b, -rgb.b)
  rgb
end

#adjust_brightness(percent) ⇒ Object

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)



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# File 'lib/color/rgb.rb', line 301

def adjust_brightness(percent)
  percent = normalize_percent(percent)
  hsl      = to_hsl
  hsl.l   *= percent
  hsl.to_rgb
end

#adjust_hue(percent) ⇒ Object

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)



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# File 'lib/color/rgb.rb', line 327

def adjust_hue(percent)
  percent = normalize_percent(percent)
  hsl      = to_hsl
  hsl.h   *= percent
  hsl.to_rgb
end

#adjust_saturation(percent) ⇒ Object

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)



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# File 'lib/color/rgb.rb', line 314

def adjust_saturation(percent)
  percent = normalize_percent(percent)
  hsl      = to_hsl
  hsl.s   *= percent
  hsl.to_rgb
end

#b ⇒ Object

Returns the blue component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 509

def b
  @b
end

#b=(bb) ⇒ Object

Sets the blue component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 522

def b=(bb)
  @b = Color.normalize(bb)
end

#blue ⇒ Object

Returns the blue component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 500

def blue
  @b * 255.0
end

#blue=(bb) ⇒ Object

Sets the blue component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 513

def blue=(bb)
  @b = Color.normalize(bb / 255.0)
end

#blue_p ⇒ Object

Returns the blue component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 504

def blue_p
  @b * 100.0
end

#blue_p=(bb) ⇒ Object

Sets the blue component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 517

def blue_p=(bb)
  @b = Color.normalize(bb / 100.0)
end

#brightness ⇒ Object

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.



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# File 'lib/color/rgb.rb', line 286

def brightness
  to_yiq.y
end

#closest_match(color_list, threshold_distance = 1000.0) ⇒ Object

Calculates and returns the closest match to this colour from a list of provided colours. Returns nil if color_list is empty or if there is no colour within the threshold_distance.

threshold_distance is used to determine the minimum colour distance permitted. Uses the CIE Delta E 1994 algorithm (CIE94) to find near matches based on perceived visual colour. The default value (1000.0) is an arbitrarily large number. The values :jnd and :just_noticeable may be passed as the threshold_distance to use the value 2.3.



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# File 'lib/color/rgb.rb', line 347

def closest_match(color_list, threshold_distance = 1000.0)
  color_list = [ color_list ].flatten(1)
  return nil if color_list.empty?

  threshold_distance = case threshold_distance
                       when :jnd, :just_noticeable
                         2.3
                       else
                         threshold_distance.to_f
                       end
  lab = to_lab
  closest_distance = threshold_distance
  best_match = nil

  color_list.each do |c|
    distance = delta_e94(lab, c.to_lab)
    if (distance < closest_distance)
      closest_distance = distance
      best_match = c
    end
  end
  best_match
end

#coerce(other) ⇒ Object

Coerces the other Color object into RGB.



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# File 'lib/color/rgb.rb', line 11

def coerce(other)
  other.to_rgb
end

#contrast(other) ⇒ Object

Outputs how much contrast this color has with another RGB color. Computes the same regardless of which one is considered foreground. If the other color does not have a #to_rgb method, this will throw an exception. Anything over about 0.22 should have a high likelihood of being legible, but the larger the difference, the more contrast. Otherwise, to be safe go with something > 0.3



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# File 'lib/color/rgb/contrast.rb', line 10

def contrast(other)
  other = coerce(other)

  # The following numbers have been set with some care.
  ((diff_brightness(other) * 0.65) +
   (diff_hue(other)        * 0.20) +
   (diff_luminosity(other) * 0.15))
end

#css_hsl ⇒ Object

Present the colour as an HSL HTML/CSS colour string (e.g., “hsl(180, 25%, 35%)”). Note that this will perform a #to_hsl operation using the default conversion formula.



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# File 'lib/color/rgb.rb', line 77

def css_hsl
  to_hsl.css_hsl
end

#css_hsla ⇒ Object

Present the colour as an HSLA (with alpha) HTML/CSS colour string (e.g., “hsla(180, 25%, 35%, 1)”). Note that this will perform a #to_hsl operation using the default conversion formula.



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# File 'lib/color/rgb.rb', line 84

def css_hsla
  to_hsl.css_hsla
end

#css_rgb ⇒ Object

Present the colour as an RGB HTML/CSS colour string (e.g., “rgb(0%, 50%, 100%)”). Note that this will perform a #to_rgb operation using the default conversion formula.



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# File 'lib/color/rgb.rb', line 58

def css_rgb
  "rgb(%3.2f%%, %3.2f%%, %3.2f%%)" % [ red_p, green_p, blue_p ]
end

#css_rgba(alpha = 1) ⇒ Object

Present the colour as an RGBA (with an optional alpha that defaults to 1) HTML/CSS colour string (e.g.,“rgb(0%, 50%, 100%, 1)”). Note that this will perform a #to_rgb operation using the default conversion formula.

Color::RGB.by_hex('ff0000').css_rgba
=> 'rgba(100.00%, 0.00%, 0.00%, 1.00)'
Color::RGB.by_hex('ff0000').css_rgba(0.2)
=> 'rgba(100.00%, 0.00%, 0.00%, 0.20)'



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# File 'lib/color/rgb.rb', line 70

def css_rgba(alpha = 1)
  "rgba(%3.2f%%, %3.2f%%, %3.2f%%, %3.2f)" % [ red_p, green_p, blue_p, alpha ]
end

#darken_by(percent) ⇒ Object

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.



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# File 'lib/color/rgb.rb', line 263

def darken_by(percent)
  mix_with(Black, percent)
end

#delta_e94(color_1, color_2, weighting_type = :graphic_arts) ⇒ Object

The Delta E (CIE94) algorithm en.wikipedia.org/wiki/Color_difference#CIE94

There is a newer version, CIEDE2000, that uses slightly more complicated math, but addresses “the perceptual uniformity issue” left lingering by the CIE94 algorithm. color_1 and color_2 are both L*a*b* hashes, rendered by #to_lab.

Since our source is treated as sRGB, we use the “graphic arts” presets for k_L, k_1, and k_2

The calculations go through LCH(ab). (?)

See also www.brucelindbloom.com/index.html?Eqn_DeltaE_CIE94.html

NOTE: This should be moved to Color::Lab.



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# File 'lib/color/rgb.rb', line 387

def delta_e94(color_1, color_2, weighting_type = :graphic_arts)
  case weighting_type
  when :graphic_arts
    k_1 = 0.045
    k_2 = 0.015
    k_L = 1
  when :textiles
    k_1 = 0.048
    k_2 = 0.014
    k_L = 2
  else
    raise ArgumentError, "Unsupported weighting type #{weighting_type}."
  end

  # delta_E = Math.sqrt(
  #   ((delta_L / (k_L * s_L)) ** 2) +
  #   ((delta_C / (k_C * s_C)) ** 2) +
  #   ((delta_H / (k_H * s_H)) ** 2)
  # )
  #
  # Under some circumstances in real computers, delta_H could be an
  # imaginary number (it's a square root value), so we're going to treat
  # this as:
  #
  # delta_E = Math.sqrt(
  #   ((delta_L / (k_L * s_L)) ** 2) +
  #   ((delta_C / (k_C * s_C)) ** 2) +
  #   (delta_H2 / ((k_H * s_H) ** 2)))
  # )
  #
  # And not perform the square root when calculating delta_H2.

  k_C = k_H = 1

  l_1, a_1, b_1 = color_1.values_at(:L, :a, :b)
  l_2, a_2, b_2 = color_2.values_at(:L, :a, :b)

  delta_a = a_1 - a_2
  delta_b = b_1 - b_2

  c_1 = Math.sqrt((a_1 ** 2) + (b_1 ** 2))
  c_2 = Math.sqrt((a_2 ** 2) + (b_2 ** 2))

  delta_L = color_1[:L] - color_2[:L]
  delta_C = c_1 - c_2

  delta_H2 = (delta_a ** 2) + (delta_b ** 2) - (delta_C ** 2)

  s_L = 1
  s_C = 1 + k_1 * c_1
  s_H = 1 + k_2 * c_1

  composite_L = (delta_L / (k_L * s_L)) ** 2
  composite_C = (delta_C / (k_C * s_C)) ** 2
  composite_H = delta_H2 / ((k_H * s_H) ** 2)
  Math.sqrt(composite_L + composite_C + composite_H)
end

#g ⇒ Object

Returns the green component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 482

def g
  @g
end

#g=(gg) ⇒ Object

Sets the green component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 495

def g=(gg)
  @g = Color.normalize(gg)
end

#green ⇒ Object

Returns the green component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 473

def green
  @g * 255.0
end

#green=(gg) ⇒ Object

Sets the green component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 486

def green=(gg)
  @g = Color.normalize(gg / 255.0)
end

#green_p ⇒ Object

Returns the green component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 477

def green_p
  @g * 100.0
end

#green_p=(gg) ⇒ Object

Sets the green component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 490

def green_p=(gg)
  @g = Color.normalize(gg / 100.0)
end

#hex ⇒ Object

Present the colour as an RGB hex triplet.



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# File 'lib/color/rgb.rb', line 37

def hex
  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

#html ⇒ Object

Present the colour as an HTML/CSS colour string.



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# File 'lib/color/rgb.rb', line 51

def html
  "##{hex}"
end

#inspect ⇒ Object 



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# File 'lib/color/rgb.rb', line 553

def inspect
  "RGB [#{html}]"
end

#lighten_by(percent) ⇒ Object

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.



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# File 'lib/color/rgb.rb', line 256

def lighten_by(percent)
  mix_with(White, percent)
end

#max_rgb_as_grayscale ⇒ Object Also known as: max_rgb_as_greyscale

Retrieve the maxmum RGB value from the current colour as a GrayScale colour



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# File 'lib/color/rgb.rb', line 548

def max_rgb_as_grayscale
  Color::GrayScale.from_fraction([@r, @g, @b].max)
end

#mix_with(mask, opacity) ⇒ Object

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



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# File 'lib/color/rgb.rb', line 269

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 ⇒ Object

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



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# File 'lib/color/rgb.rb', line 26

def pdf_fill
  PDF_FORMAT_STR % [ @r, @g, @b, "rg" ]
end

#pdf_stroke ⇒ Object

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



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# File 'lib/color/rgb.rb', line 32

def pdf_stroke
  PDF_FORMAT_STR % [ @r, @g, @b, "RG" ]
end

#r ⇒ Object

Returns the red component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 455

def r
  @r
end

#r=(rr) ⇒ Object

Sets the red component of the colour as a fraction in the range 0.0 .. 1.0.



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# File 'lib/color/rgb.rb', line 468

def r=(rr)
  @r = Color.normalize(rr)
end

#red ⇒ Object

Returns the red component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 446

def red
  @r * 255.0
end

#red=(rr) ⇒ Object

Sets the red component of the colour in the normal 0 .. 255 range.



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# File 'lib/color/rgb.rb', line 459

def red=(rr)
  @r = Color.normalize(rr / 255.0)
end

#red_p ⇒ Object

Returns the red component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 450

def red_p
  @r * 100.0
end

#red_p=(rr) ⇒ Object

Sets the red component of the colour as a percentage.



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# File 'lib/color/rgb.rb', line 463

def red_p=(rr)
  @r = Color.normalize(rr / 100.0)
end

#to_a ⇒ Object 



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# File 'lib/color/rgb.rb', line 557

def to_a
  [ r, g, b ]
end

#to_cmyk ⇒ Object

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.



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# File 'lib/color/rgb.rb', line 114

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 ⇒ Object Also known as: to_greyscale

Convert to grayscale.



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# File 'lib/color/rgb.rb', line 290

def to_grayscale
  Color::GrayScale.from_fraction(to_hsl.l)
end

#to_hsl ⇒ Object

Returns the HSL colour encoding of the RGB value. The conversions here are based on forumlas from www.easyrgb.com/math.php and elsewhere.



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# File 'lib/color/rgb.rb', line 145

def to_hsl
  min   = [ @r, @g, @b ].min
  max   = [ @r, @g, @b ].max
  delta = (max - min).to_f

  lum   = (max + min) / 2.0

  if Color.near_zero?(delta) # close to 0.0, so it's a grey
    hue = 0
    sat = 0
  else
    if Color.near_zero_or_less?(lum - 0.5)
      sat = delta / (max + min).to_f
    else
      sat = delta / (2 - max - min).to_f
    end

    # This is based on the conversion algorithm from
    # http://en.wikipedia.org/wiki/HSV_color_space#Conversion_from_RGB_to_HSL_or_HSV
    # Contributed by Adam Johnson
    sixth = 1 / 6.0
    if @r == max # Color.near_zero_or_less?(@r - max)
      hue = (sixth * ((@g - @b) / delta))
      hue += 1.0 if @g < @b
    elsif @g == max # Color.near_zero_or_less(@g - max)
      hue = (sixth * ((@b - @r) / delta)) + (1.0 / 3.0)
    elsif @b == max # Color.near_zero_or_less?(@b - max)
      hue = (sixth * ((@r - @g) / delta)) + (2.0 / 3.0)
    end

    hue += 1 if hue < 0
    hue -= 1 if hue > 1
  end
  Color::HSL.from_fraction(hue, sat, lum)
end

#to_lab(color_space = :sRGB, reference_white = [ 95.047, 100.00, 108.883 ]) ⇒ Object

Returns the L*a*b* colour encoding of the value via the XYZ colour encoding. Based on the XYZ to Lab formula presented by Bruce Lindbloom.

Currently only the sRGB colour space is supported and defaults to using a D65 reference white.



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# File 'lib/color/rgb.rb', line 217

def to_lab(color_space = :sRGB, reference_white = [ 95.047, 100.00, 108.883 ])
  xyz = to_xyz

  # Calculate the ratio of the XYZ values to the reference white.
  # http://www.brucelindbloom.com/index.html?Equations.html
  xr = xyz[:x] / reference_white[0]
  yr = xyz[:y] / reference_white[1]
  zr = xyz[:z] / reference_white[2]

  # NOTE: This should be using Rational instead of floating point values,
  # otherwise there will be discontinuities.
  # http://www.brucelindbloom.com/LContinuity.html
  epsilon = (216 / 24389.0)
  kappa   = (24389 / 27.0)

  # And now transform
  # http://en.wikipedia.org/wiki/Lab_color_space#Forward_transformation
  # There is a brief explanation there as far as the nature of the calculations,
  # as well as a much nicer looking modeling of the algebra.
  fx, fy, fz = [ xr, yr, zr ].map { |t|
    if (t > (epsilon))
      t ** (1.0 / 3)
    else # t <= epsilon
      ((kappa * t) + 16) / 116.0
      # The 4/29 here is for when t = 0 (black). 4/29 * 116 = 16, and 16 -
      # 16 = 0, which is the correct value for L* with black.
#       ((1.0/3)*((29.0/6)**2) * t) + (4.0/29)
    end
  }
  {
    :L => ((116 * fy) - 16),
    :a => (500 * (fx - fy)),
    :b => (200 * (fy - fz))
  }
end

#to_rgb(ignored = nil) ⇒ Object 



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# File 'lib/color/rgb.rb', line 130

def to_rgb(ignored = nil)
  self
end

#to_xyz(color_space = :sRGB) ⇒ Object

Returns the XYZ colour encoding of the value. Based on the RGB to XYZ formula presented by Bruce Lindbloom.

Currently only the sRGB colour space is supported.



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# File 'lib/color/rgb.rb', line 186

def to_xyz(color_space = :sRGB)
  unless color_space.to_s.downcase == 'srgb'
    raise ArgumentError, "Unsupported colour space #{color_space}."
  end

  # Inverse sRGB companding. Linearizes RGB channels with respect to
  # energy.
  r, g, b = [ @r, @g, @b ].map { |v|
    if (v > 0.04045)
      (((v + 0.055) / 1.055) ** 2.4) * 100
    else
      (v / 12.92) * 100
    end
  }

  # Convert using the RGB/XYZ matrix at:
  # http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html#WSMatrices
  {
    :x => (r * 0.4124564 + g * 0.3575761 + b * 0.1804375),
    :y => (r * 0.2126729 + g * 0.7151522 + b * 0.0721750),
    :z => (r * 0.0193339 + g * 0.1191920 + b * 0.9503041)
  }
end

#to_yiq ⇒ Object

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



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# File 'lib/color/rgb.rb', line 135

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