numpy: unique list of colors in the image

Question

I have an image img:

>>> img.shape
(200, 200, 3)

On pixel (100, 100) I have a nice color:

>>>         


        

Answer 1

The question about unique colors (or more generally unique values along a given axis) has been also asked here (in particular, see this answer). If you're seeking for the fastest available option then "void view" would be your weapon of choice:

axis=2
np.unique(
        img.view(np.dtype((np.void, img.dtype.itemsize*img.shape[axis])))
        ).view(img.dtype).reshape(-1, img.shape[axis])

For any questions related to what the script actually does, I refer the reader to the links above.