how to get random pixel index from binary image with value 1 in python?

Question

I have a binary image of large size (2000x2000). In this image most of the pixel values are zero and some of them are 1. I need to get only 100 randomly chosen pixel coordinates with value 1 from image. I am beginner in python, so please answer.

Answer 1

I'd suggest making a list of coordinates of all non-zero pixels (by checking all pixels in the image), then using random.shuffle on the list and taking the first 100 elements.

Answer 2

After importing necessary libraries like

import cv2
import numpy as np  
import pandas as pd  
import matplotlib.pyplot as plt 

gray_img = cv2.imread(img_file, cv2.IMREAD_GRAYSCALE) # grayscale

gray_img[i,j] will give pixel value at (i,j) position

Try to send all these values into a file in this format

i_positition,j_position,value_of_pixel

path = os.getcwd() + '/filename.txt'  
data = pd.read_csv(path, header=None, names=['i', 'j', 'value'])

positive = data[data['value'].isin([1])]  
negative = data[data['value'].isin([0])]

positive data frame contains all the pixel positions whose value is 1.

positive['i'] ,positive['j'] will give you list of (i,j) values of all the pixels whose value is 1.

i_val=np.asarray(positive['i'])

j_val=np.asarray(positive['j'])

Now you can randomly select any value from i_val & j_val arrays.

Note: Make sure that your pixel values will be 1 or 0. If your values are 0 and 255 then change this command

positive = data[data['value'].isin([255])]