CODE EXAMPLE FOR PYTHON

python downsample image

import numpy as np
from scipy import ndimage

def block_mean(ar, fact):
    assert isinstance(fact, int), type(fact)
    sx, sy = ar.shape
    X, Y = np.ogrid[0:sx, 0:sy]
    regions = sy/fact * (X/fact) + Y/fact
    res = ndimage.mean(ar, labels=regions, index=np.arange(regions.max() + 1))
    res.shape = (sx/fact, sy/fact)
    return res
  
 # Example:
ar = np.random.rand(20000).reshape((100, 200))
block_mean(ar, 5).shape  # (20, 40)