Class: ColorConverters::RgbConverter

Inherits:
BaseConverter show all
Defined in:
lib/color_converters/converters/rgb_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/rgb_converter.rb', line 11

def self.bounds
  { r: [0.0, 255.0], g: [0.0, 255.0], b: [0.0, 255.0], a: [0.0, 1.0] }
end

.lrgb_to_rgb(lrgb_array) ⇒ Object 



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# File 'lib/color_converters/converters/rgb_converter.rb', line 69

def self.lrgb_to_rgb(lrgb_array)
  rr, gg, bb = lrgb_array

  # Apply sRGB Companding (gamma correction) to convert from Linear RGB to non-linear sRGB.

  # This is defined by the sRGB specification (IEC 61966-2-1).

  # The exponent for the non-linear segment is 1/2.4 (approximately 0.41666...).

  # Assumption that rr, gg, bb are always positive

  r, g, b = [rr, gg, bb].map do
    if _1.to_d <= 0.0031308.to_d
      # Linear portion of the sRGB curve

      _1.to_d * 12.92.to_d
    else
      # Non-linear (gamma-corrected) portion of the sRGB curve

      # The sRGB specification uses an exponent of 1/2.4.

      #

      (1.055.to_d * (_1.to_d**(1.0.to_d / 2.4.to_d))) - 0.055.to_d

      # IMPORTANT NUMERICAL NOTE:

      # On this specific system (and confirmed by Wolfram Alpha for direct calculation),

      # the inverse power function for val**2.4 yields a result that deviates from the value expected by widely-used colour science libraries (like Bruce Lindbloom's).

      #

      # To compensate for this numerical discrepancy and ensure the final CIELAB values match standard online calculators and specifications,

      # an empirically determined exponent of 2.5 has been found to produce the correct linearized sRGB values on this environment.

      #

      # Choose 1/2.4 for strict adherence to the standard's definition (knowing your results may slightly deviate from common calculators),

      # or choose 1/2.5 to ensure your calculated linear RGB values (and thus CIELAB) match authoritative external tools on this system.

      #

      # (1.055 * (_1**(1.0 / 2.5))) - 0.055

    end
  end

  # Scale the 0-1 sRGB value to the 0-255 range for 8-bit colour components.

  r *= 255.0.to_d
  g *= 255.0.to_d
  b *= 255.0.to_d

  # Clamping RGB values to prevent out-of-gamut issues and numerical errors and ensures these values stay within the valid and expected range.

  r = r.clamp(0.0..255.0)
  g = g.clamp(0.0..255.0)
  b = b.clamp(0.0..255.0)

  [r, g, b]
end

.matches?(colour_input) ⇒ Boolean

Returns:

  • (Boolean) 


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

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

  colour_input.keys - [:r, :g, :b] == [] || colour_input.keys - [:r, :g, :b, :a] == []
end

.rgb_to_lrgb(rgb_array_frac) ⇒ Object 



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# File 'lib/color_converters/converters/rgb_converter.rb', line 36

def self.rgb_to_lrgb(rgb_array_frac)
  # [0, 1]

  r, g, b = rgb_array_frac

  # Inverse sRGB companding. Linearizes RGB channels with respect to energy.

  # Assumption that r, g, b are always positive

  rr, gg, bb = [r, g, b].map do
    if _1.to_d <= 0.04045.to_d
      _1.to_d / 12.92.to_d
    else
      # sRGB Inverse Companding (Non-linear to Linear RGB)

      # The sRGB specification (IEC 61966-2-1) defines the exponent as 2.4.

      #

      (((_1.to_d + 0.055.to_d) / 1.055.to_d)**2.4.to_d)

      # IMPORTANT NUMERICAL NOTE:

      # On this specific system (and confirmed by Wolfram Alpha for direct calculation),

      # the power function for val**2.4 yields a result that deviates from the value expected by widely-used colour science libraries (like Bruce Lindbloom's).

      #

      # To compensate for this numerical discrepancy and ensure the final CIELAB values match standard online calculators and specifications,

      # an empirically determined exponent of 2.5 has been found to produce the correct linearized sRGB values on this environment.

      #

      # Choose 2.4 for strict adherence to the standard's definition (knowing your results may slightly deviate from common calculators),

      # or choose 2.5 to ensure your calculated linear RGB values (and thus CIELAB) match authoritative external tools on this system.

      #

      # ((_1 + 0.055) / 1.055)**2.5

    end
  end

  # [0, 1]

  [rr, gg, bb]
end