but crop when necessary to keep proportions the same.

    This can both scale down and enlarge images, due in case of the

    latter, cropping is probably not the right algorithm to do in the

    first place: You are first throwing away information, when you

    don't have enough of it in the first place.

    # 1) Modify the bounding box of the original image to match the

    # requested thumb proportions.

    target_width, target_height = \

        _ensure_proportions((new_width, new_height), (image_width, image_height),)

    # 2) Use the adjusted image size to crop the original, so that we

    # have a piece of the original that we can resize to the requested

    # thumbnail size without skewing the image.

    # Note: We calculate both the horizontal and vertical axis, but only

    # one of them will be cropped, due to ``_ensure_proportions`` only

    # changing either the width or the height.

    top = (image_height - target_height) // 2

    left = (image_width - target_width) // 2

    bottom = image_height - top

    right = image_width - left

    image = image.crop((left, top, right, bottom,))

    # 3) Resize to target size; we can be sure we are not skewing due

    # to the cropping we've done.

    return image.resize((new_width, new_height), Image.ANTIALIAS)