CODEWITHSUNDEEP
pythonarraysimagenumpy
Joseph
Joseph

Reputation: 329

Replace numpy cell with values from second array based on a condition

I have two images, img1 and img2. I'm trying to find everywhere in img1 that the color [0,204,204] occurs and replace it with whatever is in img2 in the same place. I can use np.where() to find the places where that color occurs and replace it with a different color directly:

img1[np.where((img1==[0,204,204]).all(axis=2))] = [255,255,0]

I'm unsure how to grab the indices of these cells as the shape of the images are 5070000 with 3 dimensions, so, I can't display the array's effectively. Looking over the numpy documentation, I think I can do something like:

img2[img1[img1==[0,204,204]]]

to get the indices of img1 where that color occurs and then call the same array position from img2, but, I can't seem to get this syntax correct. Help?

Upvotes: 0

Views: 176

Answers (1)

sacuL
sacuL

Reputation: 51335

If I understand correctly, you can use the following:

img1[np.where((img1==[0,204,204]).all(axis=2))] = img2[np.where((img1==[0,204,204]).all(axis=2))]

This works because the syntax you had originally (np.where((img1==[0,204,204]).all(axis=2))) already returns the indices you are looking for

Example (on a small array):

img1 = np.array([[[0,204,204],[0,0,0],[1,2,3]]])

array([[[  0, 204, 204],
        [  0,   0,   0],
        [  1,   2,   3]]])

img2 = np.array([[[0,1,2],[1,1,1],[2,7,3]]])

array([[[0, 1, 2],
        [1, 1, 1],
        [2, 7, 3]]])

img1[np.where((img1==[0,204,204]).all(axis=2))] = img2[np.where((img1==[0,204,204]).all(axis=2))]

>>> img1
array([[[0, 1, 2],
        [0, 0, 0],
        [1, 2, 3]]])

Upvotes: 1

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