import pyvips

# rotate an image with centre crop and reflection fill

im = pyvips.Image.new_from_file("/home/john/pics/k2.jpg")

# pyvips rotate always fills any new pixels which appear around the image edges
# with 0 (black). To have something else in there, we need to expand the image
# first, then crop it down to just the bit we need.

# libvips 8.6 adds a "background" kwarg to similarity() and affine() that lets
# you put some other constant in the new pixels, but for now embed() is the best
# solution, especially if you want something like reflection fill.

# This sounds inefficient, but libvips is demand-driven, so pixels which are
# never used will never be calculated.

# We expand the image enough that we can be sure we can never see black, no
# matter the rotation angle or the image proportions.

new_size = 2 * max(im.width, im.height)
im2 = im.embed((new_size - im.width) / 2,
               (new_size - im.height) / 2,
               new_size,
               new_size,
               extend='mirror')

im2 = im2.similarity(angle=20)

# now crop a piece the size of the original from the centre of the rotated image

im = im2.crop((im2.width - im.width) / 2,
              (im2.height - im.height) / 2,
              im.width,
              im.height)

im.write_to_file("x.jpg")