Swapping array dimensions with NumPy

Question

When I load an image with PIL and convert it into a NumPy array:

image = Image.open("myimage.png")
pixels = np.asarray(image)

The data is stored as [x][y][channel]. I.e., the value of pixels[3, 5, 0] will be the the (3, 5) pixel, and the red component of that pixel.

However, I am using a library which requires the image to be in the format [channel][x][y]. Therefore, I am wondering how I can do this conversion?

I know that NumPy has a reshape function, but this doesn't actually allow you to "swap" over the dimensions as I want.

Any help? Thanks!

You could use the transpose method as opposed to the reshape method — tmwilson26
– tmwilson26, Commented Feb 2, 2017 at 17:09
There's swapaxes, rollaxis, and transpose. All of them allow you to permute axes in one way or another. — IanH
– IanH, Commented Feb 2, 2017 at 17:10

tmwilson26 · Accepted Answer · 2017-02-02 17:11:18Z

7

In order to get the dimensions in the order that you want, you could use the transpose method as follows:

image = Image.open("myimage.png")
pixels = np.asarray(image).transpose(2,0,1)

answered Feb 2, 2017 at 17:11

tmwilson26

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