Python PIL bitmap/png from array with mode=1

Question

Playing with PIL (and numpy) for the first time ever. I was trying to generate a black and white checkerboard image through mode=\'1\', but it doesn\'t work.

Answer 1

As pointed out in the other answer, you are running into a Pillow bug, and the accepted answer is fine.

As an alternative to PIL/Pillow, you could use pypng, or you could use numpngw, a library that I wrote to write NumPy arrays to PNG and animated PNG files. It is on github: https://github.com/WarrenWeckesser/numpngw (It has all the boilerplate files of a python package, but the essential file is numpngw.py.) It is also on PyPI.

Here's an example of using numpngw.write_png to create the checkerboard image. This creates an image with bit depth 1:

In [10]: g
Out[10]: 
array([[1, 0, 1, 0, 1, 0, 1, 0],
       [0, 1, 0, 1, 0, 1, 0, 1],
       [1, 0, 1, 0, 1, 0, 1, 0],
       [0, 1, 0, 1, 0, 1, 0, 1],
       [1, 0, 1, 0, 1, 0, 1, 0],
       [0, 1, 0, 1, 0, 1, 0, 1],
       [1, 0, 1, 0, 1, 0, 1, 0],
       [0, 1, 0, 1, 0, 1, 0, 1]], dtype=uint8)

In [11]: import numpngw

In [12]: numpngw.write_png('checkerboard.png', g, bitdepth=1)

Here's the image it creates: