Find X and Y Coordinates of a value in a python array

Question

I am trying to get the x and y coordinates of a given value in a numpy image array.

I can do it by running through the rows and columns manually with a for statement, but this seems rather slow and I am possitive there is a better way to do this.

I was trying to modify a solution I found in this post. Finding the (x,y) indexes of specific (R,G,B) color values from images stored in NumPy ndarrays

a = image
c = intensity_value

y_locs = np.where(np.all(a == c, axis=0))
x_locs = np.where(np.all(a == c, axis=1))

return np.int64(x_locs), np.int64(y_locs)

I have the np.int64 to convert the values back to int64.

I was also looking at numpy.where documentation

So exactly whats your problem now?

Kasravnd
– Kasravnd

2015-04-04 21:17:31 +00:00
Commented Apr 4, 2015 at 21:17 — Kasravnd
– Kasravnd, Commented Apr 4, 2015 at 21:17

YXD · Accepted Answer · 2015-04-04 23:41:18Z

1

I don't quite understand the problem. The axis parameter in all() runs over the colour channels (axis 2 or -1) rather than the x and y indices. Then where() will give you the coordinates of the matching values in the image:

>>> # set up data
>>> image = np.zeros((5, 4, 3), dtype=np.int)
>>> image[2, 1, :] = [7, 6, 5]
>>> # find indices
>>> np.where(np.all(image == [7, 6, 5], axis=-1))
(array([2]), array([1]))
>>>

This is really just repeating the answer you linked to. But is a bit too long for a comment. Maybe you could explain a bit more why you need to modify the previous answer? It doesn't seem like you do need to.

answered Apr 4, 2015 at 23:41

YXD

32.6k15 gold badges79 silver badges117 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Tim R Over a year ago

So I am trying to understand np.where. What I need to do is look in the rows and put all hits in an array for the rows, and then look in the columns and put in an array for the columns.

YXD Over a year ago

where returns both the rows and the columns in one go. Have a read of the documentation docs.scipy.org/doc/numpy/reference/generated/numpy.where.html

Collectives™ on Stack Overflow

Find X and Y Coordinates of a value in a python array

1 Answer 1

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related