Class: ColorConverters::CielabConverter

Inherits:
BaseConverter show all
Defined in:
lib/color_converters/converters/cielab_converter.rb

Constant Summary

Constants inherited from BaseConverter

BaseConverter::IMPORT_DP, BaseConverter::OUTPUT_DP

Instance Attribute Summary

Attributes inherited from BaseConverter

#original_value, #rgba

Class Method Summary collapse

Methods inherited from BaseConverter

#alpha, #cielab, #cielch, #cmyk, factory, #hex, #hsb, #hsl, #hsv, inherited, #initialize, #name, #oklab, #oklch, #rgb, #xyz

Constructor Details

This class inherits a constructor from ColorConverters::BaseConverter

Class Method Details

.bounds ⇒ Object 



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# File 'lib/color_converters/converters/cielab_converter.rb', line 11

def self.bounds
  { l: [0.0, 100.0], a: [-128.0, 127.0], b: [-128.0, 127.0] }
end

.cielab_to_xyz(colour_input) ⇒ Object 



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# File 'lib/color_converters/converters/cielab_converter.rb', line 34

def self.cielab_to_xyz(colour_input)
  l = colour_input[:l].to_d
  a = colour_input[:a].to_d
  b = colour_input[:b].to_d

  yy = (l + 16.0.to_d) / 116.0.to_d
  xx = (a / 500.0.to_d) + yy
  zz = yy - (b / 200.0.to_d)

  e = 216.0.to_d / 24_389.0.to_d

  x, y, z = [xx, yy, zz].map do
    if _1**3.to_d <= e
      (3.0.to_d * (6.0.to_d / 29.0.to_d) * (6.0.to_d / 29.0.to_d) * (_1 - (4.0.to_d / 29.0.to_d)))
    else
      _1**3.to_d
    end
  end

  x *= 95.047.to_d
  y *= 100.0.to_d
  z *= 108.883.to_d

  [x, y, z]
end

.matches?(colour_input) ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/color_converters/converters/cielab_converter.rb', line 5

def self.matches?(colour_input)
  return false unless colour_input.is_a?(Hash)

  colour_input.keys - [:l, :a, :b, :space] == [] && colour_input[:space].to_s == 'cie'
end

.xyz_to_cielab(xyz_array) ⇒ Object 



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# File 'lib/color_converters/converters/cielab_converter.rb', line 60

def self.xyz_to_cielab(xyz_array)
  x, y, z = xyz_array.map(&:to_d)

  # https://www.w3.org/TR/css-color-4/#color-conversion-code
  # # The D50 & D65 standard illuminant white point
  # wp_rel = [0.3457 / 0.3585, 1.0, (1.0 - 0.3457 - 0.3585) / 0.3585]
  wp_rel = [0.3127.to_d / 0.3290.to_d, 1.0.to_d, (1.0.to_d - 0.3127.to_d - 0.3290.to_d) / 0.3290.to_d].map { _1 * 100.0.to_d }

  xr, yr, zr = wp_rel

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

  e = 216.0.to_d / 24_389.0.to_d
  k = 841.0.to_d / 108.0.to_d

  # 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.
  xx, yy, zz = rel.map do
    if _1 > e
      _1**(1.0.to_d / 3.0.to_d)
    else
      (k * _1) + (4.0.to_d / 29.0.to_d)
      # 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
  end

  l = ((116.0.to_d * yy) - 16.0.to_d)
  a = (500.0.to_d * (xx - yy))
  b = (200.0.to_d * (yy - zz))

  [l, a, b]
end