Change the image background to red with numpy

Question

I'm try to change a photo's background to red, which is white right now.

Unfortunately, I got the grey background color with numpy.

Here is my code:

import imageio as imio
import matplotlib.pyplot as plt
import numpy as np

joe_data = imio.imread('./wifire/11.JPG')
print(joe_data.shape)
plt.figure(figsize=(10, 10))
plt.imshow(joe_data)

red_mask = (joe_data[:, :, 0] == 255)
green_mask = (joe_data[:, :, 1] == 255)
blue_mask = (joe_data[:, :, 2] == 255)

joe_data[red_mask] = 255
joe_data[green_mask] = 0
joe_data[blue_mask] = 0

plt.figure(figsize=(10, 10))
plt.imshow(joe_data)
# I can't change the background to blue or other colour, they are just grey

Answer 1

The mask is a 2-dimmensional array because you set one of the dimmensions in the definition, whereas joe_data is a 3-dimmensional array, try this:

joe_data[:, :, 0][red_mask] = 255
joe_data[:, :, 1][green_mask] = 0
joe_data[:, :, 2][blue_mask] = 0

here the mask and the data should have the same shape.