Class: Color::Lab

Inherits:
Base
  • Object
show all
Defined in:
lib/quadtone/color/lab.rb

Constant Summary collapse

DeltaEMethods = 
[
  :density,
  :cie76,
  :cie94,
  :cmclc
]

Instance Attribute Summary

Attributes inherited from Base

#components

Class Method Summary collapse

Instance Method Summary collapse

Methods inherited from Base

#<=>, average, colorspace_name, #eql?, from_cgats, #hash, #initialize, num_components, #to_cgats, #to_s, #to_str

Methods included from Math

#deg2rad, #rad2deg

Constructor Details

This class inherits a constructor from Color::Base

Class Method Details

.cgats_fields ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 16

def self.cgats_fields
  %w{LAB_L LAB_A LAB_B}
end

.component_names ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 12

def self.component_names
  [:l, :a, :b]
end

Instance Method Details

#a ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 24

def a
  @components[1]
end

#b ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 28

def b
  @components[2]
end

#chroma ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 36

def chroma
  # http://www.brucelindbloom.com/Eqn_Lab_to_LCH.html
  sqrt((a * a) + (b * b))
end

#delta_e(other, method = :cmclc) ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 50

def delta_e(other, method=:cmclc)
  # http://en.wikipedia.org/wiki/Color_difference
  # http://www.brucelindbloom.com/iPhone/ColorDiff.html
  l1, a1, b1 = self.l, self.a, self.b
  l2, a2, b2 = other.l, other.a, other.b
  dl = l2 - l1
  da = a1 - a2
  db = b1 - b2
  if method == :cie94 || method == :cmclc
    c1, c2 = self.chroma, other.chroma
    h1, h2 = self.hue, other.hue
    dc = c1 - c2
    dh2 = da**2 + db**2 - dc**2
    return Float::NAN if dh2 < 0
    dh = sqrt(dh2)
  end
  case method
  when :density
    dl.abs
  when :cie76
    sqrt(dl**2 + da**2 + db**2)
  when :cie94
    kl, k1, k2 = 1, 0.045, 0.015
    sqrt(
      (dl / kl)**2 +
      (dc / (1 + k1*c1))**2 +
      (dh / (1 + k2*c2)**2)
    )
  when :cmclc
    l, c = 2, 1
    sl = (l1 < 16) ?
      0.511 :
      0.040975 * l1 / (1 + 0.01765 * l1)
    sc = 0.0638 * c1 / (1 + 0.0131 * c1) + 0.638
    f = sqrt(
      (c1 ** 4) / ((c1 ** 4) + 1900)
    )
    t = (h1 >= 164 && h1 <= 345) ?
      0.56 + (0.2 * cos(deg2rad(h1 + 168))).abs :
      0.36 + (0.4 * cos(deg2rad(h1 + 35))).abs
    sh = sc * ((f * t) + 1 - f)
    sqrt(
      (dl / (l * sl)) ** 2 +
      (dc / (c * sc)) ** 2 +
      (dh / sh) ** 2
    )
  else
    raise "Unknown deltaE method: #{method.inspect}"
  end
end

#hue ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 41

def hue
  # http://www.brucelindbloom.com/Eqn_Lab_to_LCH.html
  if a == 0 && b == 0
    0
  else
    rad2deg(atan2(b, a)) % 360
  end
end

#l ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 20

def l
  @components[0]
end

#to_rgb ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 124

def to_rgb
  to_xyz.to_rgb
end

#to_xyz ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 101

def to_xyz
  # after http://www.easyrgb.com/index.php?X=MATH&H=08#text8

  y = (l + 16) / 116.0
  x = (a / 500.0) + y
  z = y - (b / 200.0)

  x, y, z = [x, y, z].map do |n|
    if (n3 = n**3) > 0.008856
      n3
    else
      (n - 16 / 116.0) / 7.787
    end
  end

  ref = Color::XYZ.standard_reference
  x *= ref.x
  y *= ref.y
  z *= ref.z

  Color::XYZ.new([x, y, z])
end

#value ⇒ Object 



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# File 'lib/quadtone/color/lab.rb', line 32

def value
  1 - (l / 100.0)
end