How do I stop PIL from swapping height/width when rotating an image 90°?

Question

I am using PIL to rotate an image. This works in general, except when I rotate the image exactly 90° or 270°, in which case the x and y measurements swap. That is, given this image:

>>> img.size
(93, 64)

If I rotate it by 89° I get this:

>>> img.rotate(89).size
(93, 64)

And by 91° I get this:

>>> img.rotate(91).size
(93, 64)

But if I rotate it by either 90° or 270°, I find the height and width swapped:

>>> img.rotate(90).size
(64, 93)
>>> img.rotate(270).size
(64, 93)

What's the correct way to prevent this?

Answer 1

I'm hoping someone comes up with a more graceful solution, but this seems to work for now:

img = Image.open('myimage.pbm')

frames = []
for angle in range(0, 365, 5):
    # rotate the image with expand=True, which makes the canvas
    # large enough to contain the entire rotated image.
    x = img.rotate(angle, expand=True)

    # crop the rotated image to the size of the original image
    x = x.crop(box=(x.size[0]/2 - img.size[0]/2,
               x.size[1]/2 - img.size[1]/2,
               x.size[0]/2 + img.size[0]/2,
               x.size[1]/2 + img.size[1]/2))

    # do stuff with the rotated image here.

For angles other than 90° and 270° this results in the same behavior as you get if you set expand=False and don't bother with the crop operation.