How to get x,y coordinates from an image for generating heatmaps (python)

Question

I am a programming beginner. I am using images and I want to analyse them with simple codes (for the beginning).

I have images (JPEG files) with black points on a white background. I would like to create a heatmap or a dense map to identify regions where I have a lot of points and where I have few points.

I saw some people are using histogram2d where I have to input x and y coordinates. I know an image is an array and therefore it contains the x,y coordinates of pixels but I dont know how I access them to use the function histogram2d for example. Can someone help me? Since I am beginner I would like to have some explanations and I would be very thankful if someone can be so kind to explain it.

Perhaps there is also another function I could use for this approach. If so, please give me some advice

Thank you in advance for helping me.

I realized that I need to get the black pots first. So I adjusted the code:

import cv2
import numpy as np
import matplotlib.pyplot as plt
import random


#read image
img = cv2.imread("C:\\Users\\die5k\\Desktop\\NeuerOrdner\\eins.jpg")

#make Numpy array from image
n = np.array(img)

#search black pixels
#and gives an array of x and y coordinates of black pixels
#blacks = np.where((n[:, :, 0:3] == [0,0,0]).all(2))

xcoords, ycoords = np.where((n[:, :, 0:3] == [0,0,0]).all(2))

print(xcoords)
print(ycoords)

When I tried the first part seperatly like above it worked well, I got two arrays with the x and y coordinates! So I putted the two codes together:

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


def getcoordinates(img):
    #make Numpy array from image
    n = np.array(img)

    #search black pixels
    #and gives an array of x and y coordinates of black pixels
    xcoords, ycoords = np.where((n[:, :, 0:3] == [0,0,0]).all(2))

    print(xcoords)
    print(ycoords)


def getHistogramm(xcoords, ycoords):
    plt.hist2d(xcoords,ycoords,bins=50,cmap=plt.cm.jet)

    plt.title("test")

    plt.savefig("test1", bbox_inches='tight')

    plt.close()


if __name__ == '__main__':
    img = cv2.imread("C:\\Users\\die5k\\Desktop\\NeuerOrdner\\eins.jpg",0)
    getcoordinates(img)
    getHistogramm(xcoords, ycoords)

And then I got an Error I do not understand.

(Annotation) C:\Users\die5k\Desktop\NeuerOrdner>python combi.py Traceback (most recent call last): File "combi.py", line 31, in getcoordinates(img) File "combi.py", line 13, in getcoordinates xcoords, ycoords = np.where((n[:, :, 0:3] == [0,0,0]).all(2)) IndexError: too many indices for array: array is 2-dimensional, but 3 were indexed

What went wrong?

By the way for this I cutted the original image so that it only contains one black dot for trying the code.

An image example which I have: enter image description here

I would like to have something like they show in this website: https://python-graph-gallery.com/86-avoid-overlapping-in-scatterplot-with-2d-density/