numpy masking/filtering

[Gribouillis]

I think you could get something by using numpy's MaskedArray type, something along the line of

import numpy as np
import numpy.ma as ma

N = 10
band = 3
x = np.tile(np.arange(N, dtype=int), (N, 1))
mask = (abs(x-x.T) <= band)

print(mask)
m = np.repeat(mask[:,:,np.newaxis], 3, axis=2)

df = np.zeros((N, N, 3), dtype=np.uint8)
view = ma.masked_array(df, mask=m)
view[:, 0] = 255

print(df)