How to add synthetic noise in an image with specified error probability

Question

I want to create synthetic noise within an image. How will I degrade the black and white image with errors, with an independent probability of error at each point. How will I do that in Python (e.g. Error probability = 0.0011)?

Answer 1

Here's an example program simply replacing the "degraded" pixels with black, using the Pillow library

from PIL import Image
import random

img = Image.open('text.png')
pixels = img.load()

for x in range(img.size[0]):
    for y in range(img.size[1]):
        if random.random() < 0.011:
            pixels[x,y] = 0 # only 1 number given since the image is grayscale

img.save('text_degraded.png')

I've increased the probability to 0.011 to make it more noticeable, here's the output