Darken or lighten a color in matplotlib

Question

Say I have a color in Matplotlib. Maybe it\'s a string (\'k\') or an rgb tuple ((0.5, 0.1, 0.8)) or even some hex (#05FA2B). Is there a

Answer 1

Using only colorsys which is part of the python standard library it is possible to scale the lighntess with just two lines of code

If you still want the option to pass non rgb values like colornames or HEX you can simply use matplotlib.colors.ColorConverter.to_rgb("#ff0000").

This method scales the lightness of an rgb color

import colorsys

def scale_lightness(rgb, scale_l):
    # convert rgb to hls
    h, l, s = colorsys.rgb_to_hls(*rgb)
    # manipulate h, l, s values and return as rgb
    return colorsys.hls_to_rgb(h, min(1, l * scale_l), s = s)

A simple demonstration. For more details have a look at the old example.

import matplotlib
import seaborn as sns

color = matplotlib.colors.ColorConverter.to_rgb("navy")
rgbs = [scale_lightness(color, scale) for scale in [0, .5, 1, 1.5, 2]]
sns.palplot(rgbs)

Old Answer

There is a Seaborn method, that easily lets you manipulate the lightness. seaborn.set_hls_values() takes a color as RGB-Tuple, HEX or HTML-name and lets you manipulate the hue, lightness and saturation.

The scaled lightness should be between 0 and 1, where 1 < scale increases the lightness and 0 ≤ scale < 1 darkens the color.

from colorsys import rgb_to_hls
import seaborn as sns

color = (1.0, 0.0, 0.0)     # RGB

print(f"Input color:    \t Lightness:  {rgb_to_hls(*color)[1]: .2g}\t RGB:  {color}")

rgbs = []
for scale in [0, .5, 1, 1.5, 2]:

    # scale the lightness (The values should be between 0 and 1)
    lightness = min(1, rgb_to_hls(*color)[1] * scale)

    # manipulate h, l, s channel of a rgb color
    rgb = sns.set_hls_values(color = color, h = None, l = lightness, s = None)

    print(f"Scale factor: {scale: .2g}\t Lightness:  {lightness: .2g}  \t RGB:  {rgb}")
    rgbs.append(rgb)

sns.palplot(rgbs)

In case you want to use other than RGB codes you need to convert your color to RGB. You could use the following command.

color = "red"               # HTML name
color = "#ff0000"           # HEX
color = matplotlib.colors.ColorConverter.to_rgb(color)

The returned values are RGB-Tuples:

Input color:        Lightness:   0.5    RGB:  (1.0, 0.0, 0.0)

Scale factor:  0    Lightness:   0      RGB:  (0.0, 0.0, 0.0)  # Black
Scale factor:  0.5  Lightness:   0.25   RGB:  (0.5, 0.0, 0.0)
Scale factor:  1    Lightness:   0.5    RGB:  (1.0, 0.0, 0.0)  # Unchanged
Scale factor:  1.5  Lightness:   0.75   RGB:  (1.0, 0.5, 0.5)
Scale factor:  2    Lightness:   1      RGB:  (1.0, 1.0, 1.0)  # White

EDIT:

Thanks @fhgd! I changed the code to actually scale the lightness and not just set it.