filtering - Filter part of image using PIL, python

Question

I can't understand how to apply blur filter to part of an image using PIL. I've tried to search with google and read PIL documentation but didn't find anything useful. Thanks for help.

Answer 1

You can crop out a section of the image, blur it, and stick it back in. Like this:

box = (30, 30, 110, 110)
ic = image.crop(box)
for i in range(10):  # with the BLUR filter, you can blur a few times to get the effect you're seeking
    ic = ic.filter(ImageFilter.BLUR)
image.paste(ic, box)

Below is the full code I used to generate the chess board, save the image, etc. (This isn't the most efficient way to generate a chessboard, etc, it's just for the demo.)

import Image, ImageDraw, ImageFilter
from itertools import cycle

def draw_chessboard(n=8, pixel_width=200):
    "Draw an n x n chessboard using PIL."
    def sq_start(i):
        "Return the x/y start coord of the square at column/row i."
        return i * pixel_width / n

    def square(i, j):
        "Return the square corners, suitable for use in PIL drawings" 
        return map(sq_start, [i, j, i + 1, j + 1])

    image = Image.new("L", (pixel_width, pixel_width))
    draw_square = ImageDraw.Draw(image).rectangle
    squares = (square(i, j)
               for i_start, j in zip(cycle((0, 1)), range(n))
               for i in range(i_start, n, 2))
    for sq in squares:
        draw_square(sq, fill='white')
    image.save("chessboard-pil.png")
    return image

image = draw_chessboard()

box = (30, 30, 110, 110)

ic = image.crop(box)

for i in range(10):
    ic = ic.filter(ImageFilter.BLUR)

image.paste(ic, box)

image.save("blurred.png")
image.show()

if __name__ == "__main__":
    draw_chessboard()