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Simple python function to get an approximate RGB value for a given wavelength
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| #!/usr/bin/env python3 | |
| import numpy as np | |
| import matplotlib.pyplot as plt | |
| def wavelength_to_rgb(wavelengths, gamma=0.8): | |
| '''This converts a given wavelength of light to an | |
| approximate RGB color value. The wavelength must be given | |
| in nanometers in the range from 380 nm through 750 nm | |
| (789 THz through 400 THz). | |
| Based on code by Dan Bruton | |
| http://www.physics.sfasu.edu/astro/color/spectra.html | |
| ''' | |
| wavelengths = np.array(wavelengths).astype(float) | |
| rgbs = np.zeros(wavelengths.shape + (3,)) | |
| attenuations = np.full(wavelengths.shape, np.nan) | |
| idx = ((wavelengths >= 380) & (wavelengths <= 440)) | |
| attenuations[idx] = 0.3 + 0.7 * (wavelengths[idx] - 380) / (440 - 380) | |
| rgbs[idx,0] = ((-(wavelengths[idx] - 440) / (440 - 380)) * attenuations[idx]) ** gamma | |
| rgbs[idx,2] = (1.0 * attenuations[idx]) ** gamma | |
| idx = ((wavelengths >= 440) & (wavelengths <= 490)) | |
| rgbs[idx,1] = ((wavelengths[idx] - 440) / (490 - 440)) ** gamma | |
| rgbs[idx,2] = 1.0 | |
| idx = ((wavelengths >= 490) & (wavelengths <= 510)) | |
| rgbs[idx,1] = 1.0 | |
| rgbs[idx,2] = (-(wavelengths[idx] - 510) / (510 - 490)) ** gamma | |
| idx = ((wavelengths >= 510) & (wavelengths <= 580)) | |
| rgbs[idx,0] = ((wavelengths[idx] - 510) / (580 - 510)) ** gamma | |
| rgbs[idx,1] = 1.0 | |
| idx = ((wavelengths >= 580) & (wavelengths <= 645)) | |
| rgbs[idx,0] = 1.0 | |
| rgbs[idx,1] = (-(wavelengths[idx] - 645) / (645 - 580)) ** gamma | |
| idx = ((wavelengths >= 645) & (wavelengths <= 750)) | |
| attenuations[idx] = 0.3 + 0.7 * (750 - wavelengths[idx]) / (750 - 645) | |
| rgbs[idx,0] = (1.0 * attenuations[idx]) ** gamma | |
| rgbs = (255*rgbs).astype(int) | |
| return rgbs | |
| # Display a simple rainbow | |
| #rgbs = wavelength_to_rgb(np.arange(380,750,30)) | |
| #plt.imshow(rgbs[np.newaxis,:,:]) | |
| #plt.show() | |
| # Display a 3 by 3 grid with a choice of wavelengths | |
| gridlambdas = np.zeros((3,3)) | |
| gridlambdas[0,0] = 380 | |
| gridlambdas[0,1] = 420 | |
| gridlambdas[0,2] = 460 | |
| gridlambdas[1,0] = 500 | |
| gridlambdas[1,1] = 540 | |
| gridlambdas[1,2] = 580 | |
| gridlambdas[2,0] = 620 | |
| gridlambdas[2,1] = 660 | |
| gridlambdas[2,2] = 700 | |
| gridrgbs = wavelength_to_rgb(gridlambdas) | |
| plt.figure() | |
| plt.imshow(gridrgbs) | |
| plt.title("Example wavelength grid") | |
| ax = plt.gca(); | |
| ax.grid(color='k', linestyle='-', linewidth=2) | |
| ax.set_xticks(np.arange(-.5, 3, 1)); | |
| ax.set_yticks(np.arange(-.5, 3, 1)); | |
| ax.set_xticklabels([]) | |
| ax.set_yticklabels([]) | |
| ax.tick_params(length=0) | |
| for i in range(3): | |
| for j in range(3): | |
| plt.text(j, i, f"{gridlambdas[i,j]:.0f} nm", | |
| horizontalalignment='center', | |
| verticalalignment='center', | |
| backgroundcolor=(1,1,1,0.5), | |
| color='black') | |
| plt.show() |
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