Extract coordinates from image to numpy-CodePudding

How to get coordinates of image pixels in the following form:

array([[x1 , y1],
       [ x2, y2],
           ...,])

I need them in this particular form as an input for another tool (tda-mapper).

So far, I have come to the idea that I need to sample from the image, but I haven't managed to make it yet. I would really appreciate any advice!

P.S. this is just a toy example for testing.

CodePudding user response：

You could use one of the solutions mentioned here to read in an image to a numpy array: Importing PNG files into Numpy?

And then you could use the numpy.argwhere function numpy.argwhere(image_array > treshold) to return the indices where the gray value is larger than some threshold

import matplotlib.pyplot as plt
import numpy as np

im = plt.imread('3zu5i.png')

#https://stackoverflow.com/questions/12201577/how-can-i-convert-an-rgb-image-into-grayscale-in-python
def rgb2gray(rgb):
    return np.dot(rgb[...,:3], [0.2989, 0.5870, 0.1140])

grey = rgb2gray(im)
coordinates = np.argwhere(grey < 0.99)

That should return an array containing the array indices with grayscale values larger than some threshold

array([[ 41, 280],
       [ 41, 281],
       [ 41, 282],
       ...,
       [372, 299],
       [372, 300],
       [372, 301]])