How to make a checkerboard in numpy?

Question

I\'m using numpy to initialize a pixel array to a gray checkerboard (the classic representation for \"no pixels\", or transparent). It seems like there ought to be a whizzy

Answer 1

Very very late, but I needed a solution that allows for a non-unit checker size on an arbitrarily sized checkerboard. Here's a simple and fast solution:

import numpy as np

def checkerboard(shape, dw):
    """Create checkerboard pattern, each square having width ``dw``.

    Returns a numpy boolean array.
    """
    # Create individual block
    block = np.zeros((dw * 2, dw * 2), dtype=bool)
    block[dw:, :dw] = 1
    block[:dw, dw:] = 1

    # Tile until we exceed the size of the mask, then trim
    repeat = (np.array(shape) + dw * 2) // np.array(block.shape)
    trim = tuple(slice(None, s) for s in shape)
    checkers = np.tile(block, repeat)[trim]

    assert checkers.shape == shape
    return checkers

To convert the checkerboard squares to colors, you could do:

checkers = checkerboard(shape, dw)
img = np.empty_like(checkers, dtype=np.uint8)
img[checkers] = 0xAA
img[~checkers] = 0x99