gistfile1.py

from scipy.misc import imread, imsave
from scipy import ndimage
import numpy as np
import math

def circle(radius):
    """ Product a boolean array with a shape of circle inside (True inside the
    circle and False outside). """
    assert radius >= 1
    radius -= 1
    size = (radius * 2) + 1
    y, x = np.ogrid[-radius:size - radius, -radius:size - radius]
    mask = x ** 2 + y ** 2 <= radius ** 2
    array = np.full((size, size), False, dtype=bool)
    array[mask] = True
    return array

if __name__ == '__main__':
    input_filename = 'Astar_inv.png'
    output_filename = 'output.png'
    radius = 10 # in pixel
    bot_radius = 350.0 # in mm
    mm_per_pixel = 2.0 # in mm / pixel

    img = imread(input_filename)
    bool_img = img.astype(bool)

    mask = circle(radius)
    iterations = math.ceil(bot_radius / mm_per_pixel / radius)

    masked_img = ndimage.morphology.binary_dilation(
            bool_img[:,:], structure=mask, iterations=iterations)
    out_img = masked_img.astype(np.uint8) * 255
    imsave(output_filename, out_img)