Class: ColorDiff::Ciede2000

Inherits:
Object
  • Object
show all
Defined in:
lib/color_diff/ciede2000.rb

Class Method Summary collapse

Class Method Details

.a_hp_f(c1, c2, h1p, h2p) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 100

def self.a_hp_f(c1, c2, h1p, h2p)
  sum = h1p + h2p
  diff = h1p - h2p

  if c1 * c2 == 0
    sum
  elsif diff.abs <= 180
    sum / 2.0
  elsif diff.abs > 180 && sum < 360
    (sum + 360) / 2.0
  elsif diff.abs > 180 && sum >= 360
    (sum - 360) / 2.0
  end
end

.degrees(n) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 67

def self.degrees(n)
  180 / Math::PI * n
end

.dhp_f(c1, c2, h1p, h2p) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 86

def self.dhp_f(c1, c2, h1p, h2p)
  diff = h2p - h1p

  if c1 * c2 == 0
    0
  elsif diff.abs <= 180
    diff
  elsif diff > 180
    diff - 360
  elsif diff < -180
    diff + 360
  end
end

.diff(c1, c2) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 3

def self.diff(c1, c2)
  # get lab values for color 1
  l1 = c1.l
  a1 = c1.a
  b1 = c1.b

  # get lab values for color 2
  l2 = c2.l
  a2 = c2.a
  b2 = c2.b

  # weight factors
  kl = 1
  kc = 1
  kh = 1

  # Step 1: Calculate c1p, c2p, h1p, h2p
  #
  c1 = Math.sqrt((a1 ** 2) + (b1 ** 2))
  c2 = Math.sqrt((a2 ** 2) + (b2 ** 2))

  a_c1_c2 = (c1 + c2) / 2.0

  g = 0.5 * (1 - Math.sqrt((a_c1_c2 ** 7.0) / ((a_c1_c2 ** 7.0) + (25.0 ** 7.0))))

  a1p = (1.0 + g) * a1
  a2p = (1.0 + g) * a2
  c1p = Math.sqrt((a1p ** 2) + (b1 ** 2))
  c2p = Math.sqrt((a2p ** 2) + (b2 ** 2))
  h1p = hp_f(b1, a1p)
  h2p = hp_f(b2, a2p)

  # Step 2: calculate dlp, dcp, dhp
  #
  dlp = l2 - l1
  dcp = c2p - c1p
  dhp_tmp = dhp_f(c1, c2, h1p, h2p)
  dhp = 2 * Math.sqrt(c1p * c2p) * Math.sin(radians(dhp_tmp) / 2.0)

  # Step 3: calculate CIEDE2000 Color-Difference
  #
  a_l = (l1 + l2) / 2.0
  a_cp = (c1p + c2p) / 2.0
  a_hp = a_hp_f(c1, c2, h1p, h2p)
  t = 1 -
      0.17 * Math.cos(radians(a_hp - 30)) +
      0.24 * Math.cos(radians(2 * a_hp)) +
      0.32 * Math.cos(radians(3 * a_hp + 6)) -
      0.20 * Math.cos(radians(4 * a_hp - 63))
  d_ro = 30 * Math.exp(-(((a_hp - 275) / 25) ** 2))
  rc = Math.sqrt((a_cp ** 7.0) / ((a_cp ** 7.0) + (25.0 ** 7.0)))
  sl = 1 + ((0.015 * ((a_l - 50) ** 2)) / Math.sqrt(20 + ((a_l - 50) ** 2.0)))
  sc = 1 + 0.045 * a_cp
  sh = 1 + 0.015 * a_cp * t
  rt = -2 * rc * Math.sin(radians(2 * d_ro))
  de = Math.sqrt(
         ((dlp / (sl * kl)) ** 2) +
         ((dcp / (sc * kc)) ** 2) +
         ((dhp / (sh * kh)) ** 2) + 
         rt * (dcp / (sc * kc)) * (dhp / (sh * kh)) )

  de
end

.hp_f(x, y) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 75

def self.hp_f(x, y)
  0 if x.zero? && y.zero?

  tmphp = degrees Math.atan2(x, y)
  if tmphp >= 0
    tmphp
  else
    tmphp + 360
  end
end

.radians(n) ⇒ Object 



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# File 'lib/color_diff/ciede2000.rb', line 71

def self.radians(n)
  Math::PI / 180 * n
end