How to map number to color using matplotlib's colormap?

Question

Consider a variable x containing a floating point number. I want to use matplotlib’s colormaps to map this number to a color, but not plot anything. Basically, I want to be able to choose the colormap with mpl.cm.autumn for example, use mpl.colors.Normalize(vmin = -20, vmax = 10) to set the range, and then map x to the corresponding color. But I really don’t get the documentation of mpl.cm, so if anyone could give me a hint.

Asked By: Psirus

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Source

Answer 1

It’s as simple as cm.hot(0.3):

import matplotlib.cm as cm
    
print(cm.hot(0.3))

(0.8240081481370484, 0.0, 0.0, 1.0)

If you also want to have the normalizer, use

import matplotlib as mpl
import matplotlib.cm as cm
   
norm = mpl.colors.Normalize(vmin=-20, vmax=10)
cmap = cm.hot
x = 0.3

m = cm.ScalarMappable(norm=norm, cmap=cmap)
print(m.to_rgba(x))

(1.0, 0.8225486412996345, 0.0, 1.0)

Answered By: David Zwicker

Answer 2

You can get a color from a colormap by supplying an argument between 0 and 1, e.g. cm.autumn(0.5).

If there is a normalization instance in the game, use the return of the Normalization instead:

import matplotlib.cm as cm
from matplotlib.colors import Normalize

cmap = cm.autumn
norm = Normalize(vmin=-20, vmax=10)
print cmap(norm(5))

Answered By: ImportanceOfBeingErnest

Answer 3

Number value to colormap color

import matplotlib.cm as cm
import matplotlib as matplotlib

def color_map_color(value, cmap_name='Wistia', vmin=0, vmax=1):
    # norm = plt.Normalize(vmin, vmax)
    norm = matplotlib.colors.Normalize(vmin=vmin, vmax=vmax)
    cmap = cm.get_cmap(cmap_name)  # PiYG
    rgb = cmap(norm(abs(value)))[:3]  # will return rgba, we take only first 3 so we get rgb
    color = matplotlib.colors.rgb2hex(rgb)
    return color

Answered By: khnh123

How to map number to color using matplotlib's colormap?

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