lambda2color: Wavelength-to-RGB Conversion

A lightweight Python library to convert light wavelengths (in nanometers) into corresponding RGB colors using the CIE 1931 XYZ color space.

Features

• Convert wavelengths (380–780 nm) to RGB values.
• Based on the CIE 1931 color matching functions.
• Supports custom illuminants and color spaces.

Installation

pip install lambda2color

Usage

from lambda2color import Lambda2color, xyz_from_xy

# Define a standard white illuminant (D65)
illuminant_D65 = xyz_from_xy(0.3127, 0.3291)

# Initialize color space conversion for sRGB
cs_srgb = Lambda2color(
    red=xyz_from_xy(0.64, 0.33),
    green=xyz_from_xy(0.30, 0.60),
    blue=xyz_from_xy(0.15, 0.06),
    white=illuminant_D65
)

# Convert wavelengths to RGB
wavelengths = cs_srgb.cmf[1:, 0]
N_wavelengths = len(wavelengths)
hues = np.zeros((N_wavelengths, 3))
for i_wavelength in range(N_wavelengths):
    spec = np.zeros((N_wavelengths+1))
    spec[i_wavelength] = 1
    hues[i_wavelength, :] = cs_srgb.spec_to_rgb(spec)

# give for S, M and L cones' peak sensitivities
for spec, color in [(445, 'blue'), (555, 'green'), (600, 'red')]:
  i_wavelength = np.argmin(np.abs(wavelengths - spec))
  print(f' RGB for the {color=} at wavelength {wavelengths[i_wavelength]} nm: {hues[i_wavelength, :]}')

Documentation

• Full documentation
• CIE 1931 XYZ color space

Visualizations

CIE Color Matching Functions

Spectral Colors

Advanced Use Cases

• Computing the color of the sky