Crate colcon

Simple colorspace conversions in pure Rust.

All conversions are in-place, except when converting to/from integer and hexadecimal. Formulas are generally taken from Wikipedia with correctness verified against both https://www.easyrgb.com and BABL.

Helmholtz-Kohlrausch compensation formulae sourced from https://onlinelibrary.wiley.com/doi/10.1002/col.22839

Currently, everything seems to check out except CIE XYZ. The Wikipedia formula matches EasyRGB, but BABL uses something different.

This crate references Standard Illuminant D65 when converting to/from the CIE colorspace. The feature flag D50 changes this to Illuminant D50, used by BABL (GIMP) and possibly other programs.

Enums

• Space
  Defines colorspace pixels will take.

Constants

• D50
  Illuminant D50, aka “printing” illuminant. Used by BABL/GIMP + others over D65, not sure why.
• D65
  ‘Standard’ Illuminant D65.
• HIGH2023_MEAN
  Mean value of the HK delta, High et al 2023 implementation. Measured with 36000 steps in the hk_exmample file @ 100 C(ab) Cannot make a const fn: https://github.com/rust-lang/rust/issues/57241

Functions

• convert_space
  Runs conversion functions to convert pixel from one Space to another in the least possible moves.
• convert_space_alpha
  Same as convert_space, ignores the 4th value in pixel. Just a convenience function.
• correct_gamma
  Gamma corrects a single linear light value
• expand_gamma
  Expand gamma of a single value to linear light
• hex_to_irgb
  Create integer RGB set from hex string. Not RGB specific, but other formats typically aren’t represented as hexadecimal.
• hk_comp_2023
  Compensates LCH’s L value for the Helmholtz-Kohlrausch effect. High et al 2023 implementation.
• hk_delta_2023
  Returns difference in perceptual lightness based on hue, aka the Helmholtz-Kohlrausch effect. High et al 2023 implementation.
• hsv_to_srgb
  Convert from HSV to sRGB.
• irgb_to_hex
  Create a hexadecimal string from integer RGB. Not RGB specific, but other formats typically aren’t represented as hexadecimal.
• irgb_to_srgb
  Convert integer (0..255) RGB to floating (0.0..1.0) RGB. Not RGB specific, but other formats typically aren’t represented as integers.
• lab_to_lch
  Convert from CIE LAB to CIE LCH. https://en.wikipedia.org/wiki/CIELAB_color_space#Cylindrical_model
• lab_to_xyz
  Convert from CIE LAB to CIE XYZ. https://en.wikipedia.org/wiki/CIELAB_color_space#From_CIELAB_to_CIEXYZ
• lch_to_lab
  Convert from CIE LCH to CIE LAB. https://en.wikipedia.org/wiki/CIELAB_color_space#Cylindrical_model
• lrgb_to_srgb
  Convert from Linear Light RGB to sRGB. https://en.wikipedia.org/wiki/SRGB#From_CIE_XYZ_to_sRGB
• lrgb_to_xyz
  Convert from Linear Light RGB to CIE XYZ. https://en.wikipedia.org/wiki/SRGB#From_sRGB_to_CIE_XYZ
• srgb_to_hsv
  Convert from sRGB to HSV.
• srgb_to_irgb
  Convert floating (0.0..1.0) RGB to integer (0..255) RGB. Simply clips values > 1.0 && < 0.0. Not RGB specific, but other formats typically aren’t represented as integers.
• srgb_to_lrgb
  Convert from sRGB to Linear Light RGB. https://en.wikipedia.org/wiki/SRGB#From_sRGB_to_CIE_XYZ
• xyz_to_lab
  Convert from CIE XYZ to CIE LAB. https://en.wikipedia.org/wiki/CIELAB_color_space#From_CIEXYZ_to_CIELAB
• xyz_to_lrgb
  Convert from CIE XYZ to Linear Light RGB. https://en.wikipedia.org/wiki/SRGB#From_CIE_XYZ_to_sRGB