How to I make a image from numpy array in python?

Question

I want to map each numpy array to a color to create an image. For example: if I have the numpy array:

[ [0 0 1 3] 
[0 2 4 5]
[1 2 3 6] ]

I want to make an image by mapping all values below 3 to blue like

[ [blue blue sky-blue green]
[blue sky-blue green green] 
[blue sky-blue green green]

This is answered fairly well here: stackoverflow.com/questions/44890720/… — Stephen Klein
– Stephen Klein, Commented Apr 26, 2022 at 23:36

Mark · Accepted Answer · 2022-04-26 23:42:34Z

2

You can make a two-color color map. Then make an array with 1 or 0 depending on your condition and pass both to pyplot.imshow():

import numpy as np

from matplotlib import pyplot as plt
from matplotlib.colors import ListedColormap

# white and blue
color = ListedColormap([(1,1,1), (0,0,1)])

a = np.array([
    [0, 0, 1, 3], 
    [0, 2, 4, 5],
    [1, 2, 3, 6] 
])

plt.axis('off')
plt.imshow(a < 3, cmap=color)

answered Apr 26, 2022 at 23:42

Mark

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3 Comments

Life rocks Over a year ago

Can i make 3-4 colors with this?

Mark Over a year ago

Yes. You an make a colormap with more colors, or use one of the built-in ones. Then you need an array with more values describing where to use the colors.

Life rocks Over a year ago

Can you give an example for 4 color map?

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