[FIXED] python imshow, set certain value to defined color

Issue

I have a RGB Image, which I plot with matplotlib.pyplot.imshow and it works fine. But now I want to change the plot, that where the value of the picture is e.g 1, the color of the plot should change to white at all this positions.

Is there a way to do this?

Solution

Assuming that your image is a single-channel image rather than a three-channel image, the required task can be performed by defining a palette that maps indices (e.g. gray level intensities or picture values) into colors:

import numpy as np
import matplotlib.pyplot as plt

palette = np.array([[  0,   0,   0],   # black
                    [255,   0,   0],   # red
                    [  0, 255,   0],   # green
                    [  0,   0, 255],   # blue
                    [255, 255, 255]])  # white
I = np.array([[ 0, 1, 2, 0],    # 2 rows, 4 columns, 1 channel
              [ 0, 3, 4, 0]])

Image conversion is efficiently accomplished through NumPy's broadcasting:

RGB = palette[I]

And this is how the transformed image looks like:

>>> RGB
array([[[  0,  0,    0],  # 2 rows, 4 columns, 3 channels
        [255,  0,    0],
        [  0, 255,   0],
        [  0,   0,   0]],
       
       [[  0,   0,   0],
        [  0,   0, 255],
        [255, 255, 255],
        [  0,   0,   0]]])

plt.imshow(RGB)

Answered By - Tonechas