Detect index of multiple maximum in a 2D array

Question

Let's say I have a 2D array with a size of m x n elements. Now, I want to get the indices of all maximums. So the result should be something like: [(m1, n1), (m2, n2)] where m and n indicate the x and y coordinates of my maximums.

With only one maximum its quite easy, but with more, I'm getting stuck.

import numpy as np

pixel = np.array([[0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 189, 12, 0, 0, 1, 0, 0, 0, 0],
                  [0, 6, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 0, 0, 1, 0, 0, 0, 203, 9, 0],
                  [0, 0, 0, 0, 0, 0, 0, 12, 0, 0],
                  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0],
                  [0, 0, 5, 245, 0, 0, 0, 7, 4, 0],
                  [0, 0, 0, 0, 0, 0, 0, 250, 8, 0],
                  [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]])
result = np.where(pixel == pixel.max())

print("cross detection at y:", result[0][0], "x:", result[1][0])

print(pixel)

Does somebody have an idea? It would be great, thanks!

Does this answer your question? How to make numpy.argmax return all occurrences of the maximum? — Mohammed Deifallah
– Mohammed Deifallah, Commented Jan 19, 2020 at 11:03
2nd try: basically I have an image which contains some blurred spots and I want to detect the pixel, where these spots are. For example, I have 4 spots, than I expect a list with 4 x,y coordinates. Because of the imaging structure, I know that two points cannot be closer than 20 pixels. Maybe now it gets clearer.. — Bakira
– Bakira, Commented Jan 19, 2020 at 20:54

Shubham Shaswat · Accepted Answer · 2020-01-19 20:11:53Z

2

Try this:

x,y = np.where(pixel == np.max(pixel))

this will return x axis and y axis of all the elements with maximum values Now,for your question you can do

np.array((x,y)).T

for this last code I look up to this question

edited Jan 19, 2020 at 20:11

answered Jan 19, 2020 at 14:29

Shubham Shaswat

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3 Comments

Kevin Over a year ago

Can you add an explanation to explain what this does?

Shubham Shaswat Over a year ago

@squareskittles this will return an array of the all the x-axis and an array of all the y-axis of the element having maximum values.

Kevin Over a year ago

Please edit your answer to include this explanation.

Stoufa · Accepted Answer · 2020-01-19 11:07:32Z

-1

Try numpy.argmax, it returns the indices of the maximum values along an axis.

answered Jan 19, 2020 at 11:07

Stoufa

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1 Comment

cards Over a year ago

...and as written in the link you provide "In case of multiple occurrences of the maximum values, the indices corresponding to the first occurrence are returned.". So, a unique maximum per axis

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