Getting individual colors from a color map in matplotlib
If you have a Colormap from
cmap = matplotlib.cm.get_cmap('Spectral')
how can you get a particular colour out of it between 0 and 1, where 0.0 is the first colour in the map and 1.0 is the last colour in the map?
Ideally I would be able to get the middle colour in the map by doing:
>>> do_some_magic(cmap, 0.5) # Return an RGBA tuplet (0.1, 0.2, 0.3, 1.0)
You can do this with the code below, and the code in your question was actually very close to what you needed, all you have to do is call the
cmap object you have.
import matplotlib cmap = matplotlib.cm.get_cmap('Spectral') rgba = cmap(0.5) print(rgba) # (0.99807766255210428, 0.99923106502084169, 0.74602077638401709, 1.0)
For values outside of the range [0.0, 1.0] it will return the under and over colour (respectively). This, by default, is the minimum and maximum colour within the range (so 0.0 and 1.0). This default can be changed with
For "special" numbers such as
np.inf the default is to use the 0.0 value, this can be changed using
cmap.set_bad() similarly to under and over as above.
Finally it may be necessary for you to normalize your data such that it conforms to the range
[0.0, 1.0]. This can be done using
matplotlib.colors.Normalize simply as shown in the small example below where the arguments
vmax describe what numbers should be mapped to 0.0 and 1.0 respectively.
import matplotlib norm = matplotlib.colors.Normalize(vmin=10.0, vmax=20.0) print(norm(15.0)) # 0.5
A logarithmic normaliser (matplotlib.colors.LogNorm) is also available for data ranges with a large range of values.
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