Colour A Binary Matrix Matplotlib

highlightc = np.zeros([N, N]) print highlightc c = len(highlightc) colour = [0.21]*c colour = np.array(colour) print colour for x, y in hl: highlightc[x, y] = 1##set so binary

Solution 1:

ax.imshow(X) adjusts the color scale so that the lowest value in X is mapped to the lowest color, and the highest value in X is mapped to the highest color in the cmap.

When you multiply highlight by a constant colour, the highest value in X drops from 1 to 0.21, but that has no effect on ax.imshow since the color scale gets adjusted as well, thwarting your intention.

If, however, you supply vmin=0, vmax=1 parameters, then ax.imshow will not adjust the color range -- it will associate 0 with the lowest color and 1 with the highest:

import numpy as np
import matplotlib.pyplot as plt

N = 150
highlightc = np.zeros([N, N])

M = 1000
hl = np.random.randint(N, size=(M, 2))
highlightc[zip(*hl)] = 1

colour = 0.21
fig, ax = plt.subplots()
h = ax.imshow(
    (highlightc * colour), interpolation='nearest', cmap=plt.cm.spectral_r,
    vmin=0, vmax=1)
plt.show()