Class: Abachrome::Converters::OklabToLrgb

Inherits:
Base
  • Object
show all
Defined in:
lib/abachrome/converters/oklab_to_lrgb.rb

Instance Attribute Summary

Attributes inherited from Base

#from_space, #to_space

Class Method Summary collapse

Methods inherited from Base

#can_convert?, #convert, find_converter, #initialize, raise_unless, register

Constructor Details

This class inherits a constructor from Abachrome::Converters::Base

Class Method Details

.convert(oklab_color) ⇒ Abachrome::Color

Converts a color from OKLAB color space to linear RGB (LRGB) color space.

This method performs a two-step conversion:

  1. OKLAB to LMS (cone response space)

  2. LMS to LRGB (linear RGB)

the same alpha as the input color

Parameters:

Returns:

Raises:

  • (ArgumentError) —

    If the input color is not in OKLAB color space



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# File 'lib/abachrome/converters/oklab_to_lrgb.rb', line 34

def self.convert(oklab_color)
  raise_unless oklab_color, :oklab

  l_ok, a_ok, b_ok = oklab_color.coordinates.map { |_| AbcDecimal(_) }

  # Step 1: OKLAB to L'M'S' (cone responses, non-linear)
  # These are the M_lms_prime_from_oklab matrix operations.
  l_prime = AbcDecimal(l_ok + (AD("0.39633779217376785678") * a_ok) + (AD("0.21580375806075880339") * b_ok))
  m_prime = AbcDecimal(l_ok - (a_ok * AD("0.1055613423236563494")) - (b_ok * AD("0.063854174771705903402"))) # Note: original OklabToLms had + (b * AD("-0.063..."))
  s_prime = AbcDecimal(l_ok - (a_ok * AD("0.089484182094965759684")) - (b_ok * AD("1.2914855378640917399"))) # Note: original OklabToLms had + (b * AD("-1.291..."))


  # Step 2: L'M'S' to LMS (cubing)
  l_lms = l_prime**3
  m_lms = m_prime**3
  s_lms = s_prime**3

  # Step 3: LMS to LRGB
  # Using matrix M_lrgb_from_lms (OKLAB specific)
  r_lrgb = (l_lms * AD("4.07674166134799"))   + (m_lms * AD("-3.307711590408193")) + (s_lms * AD("0.230969928729428"))
  g_lrgb = (l_lms * AD("-1.2684380040921763")) + (m_lms * AD("2.6097574006633715")) + (s_lms * AD("-0.3413193963102197"))
  b_lrgb = (l_lms * AD("-0.004196086541837188"))+ (m_lms * AD("-0.7034186144594493")) + (s_lms * AD("1.7076147009309444"))

  # Clamp LRGB values to be non-negative (as done in LmsToLrgb.rb)
  # It's also common to clamp to [0, 1] range after conversion from a wider gamut space
  # For LRGB, often just ensuring non-negative is done, and further clamping happens
  # when converting to sRGB or other display spaces.
  # Here, we'll ensure non-negative as per LmsToLrgb.
  output_coords = [r_lrgb, g_lrgb, b_lrgb].map { |it| [it, AD(0)].max }


  Color.new(ColorSpace.find(:lrgb), output_coords, oklab_color.alpha)
end