How to invert colors of image with PIL (Python-Imaging)?

Question

I need to convert series of images drawn as white on black background letters to images where white and black are inverted (as negative). How can I achieve this using PIL?

Answer 1

For anyone working with an image in "1" mode (i.e., 1-bit pixels, black and white, stored with one pixel per byte -- see docs), you need to convert it into "L" mode before calling PIL.ImageOps.invert.

Thus:

im = im.convert('L')
im = ImageOps.invert(im)
im = im.convert('1')