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Created March 6, 2014 19:12
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A script to randomize the pixels in an image, so long as they're within a mask.
#!/usr/bin/env python
import sys
import argparse
from PIL import Image
import numpy as np
def scramble_ary(img_ar, mask_ar):
Randomly scamble the pixels in img_ar for which mask_ar is true.
img_ar should be NxM (probably 3 or 4 -- rgb or rgba)
mask_ar should be Nx1 (boolean)
Returns an array shaped like img_ar.
idxs_orig = np.arange(img_ar.shape[0])
idxs_new = np.copy(idxs_orig)
shuffle_orig = np.where(mask_ar)[0]
shuffle_new = np.copy(shuffle_orig)
idxs_new[shuffle_new] = idxs_orig[shuffle_orig]
img_out = np.copy(img_ar)
img_out[idxs_new] = img_ar[idxs_orig]
return img_out
def make_flat_mask(mask_file, expected_shape):
Make a 1-dimensional boolean mask -- True wherever the image is non-black.
Raise a RuntimeError if the mask's shape is not expected_shape.
# Open the imagem convert it to greyscale, and make an array.
mask_ar = np.array("L"))
if not np.array_equal(mask_ar.shape[0:2], expected_shape[0:2]):
raise RuntimeError("mask must be the same shape as in_file")
mask_ar = mask_ar.reshape(expected_shape[0]*expected_shape[1])
return (mask_ar > 0)
def scramble_image(in_file, mask_file=None):
img_ar = np.array(
num_pix = img_ar.shape[0]*img_ar.shape[1]
img_flat = img_ar.reshape(num_pix, -1)
mask = np.ones(num_pix, dtype=bool)
if mask_file is not None:
mask = make_flat_mask(mask_file, img_ar.shape)
scrambled = scramble_ary(img_flat, mask)
return Image.fromarray(scrambled.reshape(img_ar.shape))
def main(in_file, out_file, mask=None):
out_img = scramble_image(in_file, mask)
def parse_args():
parser = argparse.ArgumentParser(
description="Randomly shuffle the pixels in an image.")
'--mask', nargs='?', default=None,
help="a mask, should be nonzero for pixels you want scrambled")
return parser.parse_args()
if __name__ == '__main__':
args = parse_args()
sys.exit(main(args.in_file, args.out_file, args.mask))
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