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## "colour.HSL_to_RGB" definition provides incorrect RGB values for S = 1.

See original GitHub issue

### Issue Description

When one creates an array of hsl values `HSL = numpy.array([[0, 0, .5], [0, 1, .5]])`, and then one converts HSL to RGB using `RGB = colour.HSL_to_RGB(HSL)` one finds that `RGB[0] = RGB[1]`.

This should not be the case, as it should be: `RGB[1] = array([1, 0, 0])`, while the package gives back: `RGB[1] = array([0.5, 0.5, 0.5])`

If one creates an HSL hue-page, as shown with the problem above, the problem is clearly demonstrated as simply this package reverts values of S = 1 to S = 0.

I created a function to create and save HSL hue-pages through the process below:

``````import numpy as np
import colour
from PIL import Image as im

def plot_HSL_huepage(hue):
s = np.arange(0, 100.1, .1) / 100
l = np.arange(0, 100.1, .1) / 100
mesh = np.array(np.meshgrid(s, l))
combinations = mesh.T.reshape(-1, 2)
h = np.full((combinations.shape[0]), hue)/360
hsl = np.stack([h, combinations[:,0], combinations[:,1]], axis = -1)
srgb = colour.HSL_to_RGB(hsl)
srgb = (srgb*255).astype(np.uint8)
RGB = np.reshape(srgb, (s.size, l.size, 3))
data = im.fromarray(RGB)
data = data.rotate(90)
data.save('hsl_huepage_h={}.png'.format(hue))
``````

When one then runs the function for HSL hues of 0, 60, 120, 240, and 300 as shown below:

``````h_values = np.array([0, 60, 120, 240, 300])
for x in h_values:
plot_HSL_huepage(x)
``````

when one opens the hue page png, no matter the hue, one sees that the values for S = 1 are the same grey values as S = 0.

I hope this issue submission is clear, I have never written one before. I only learned python because I wanted to use this package, and I am grateful for the amount of work put into making this package.

What can I do to get the correct RGB values using the `HSL_to_RGB` function?

### Issue Analytics

• State:
• Created 2 years ago
• Comments:7 (5 by maintainers)

#### Top GitHub Comments

1reaction
KelSolaarcommented, Nov 2, 2020

Ah! Thanks for the kind words @nadersadoughi and glad to have people like you on-board! A key motivation for Colour was to democratize colour science and have it escape the Matlab sandbox! 😃

1reaction

@KelSolaar In fact, thank you for very quickly finding the solution! This is the very reason why I switched over from Matlab color packages to yours in python, because of this open-source community where we can make color better, together.

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