from pylab import imshow

import numpy as np

import mahotas

wally = mahotas.imread('waldo.jpg')

imshow(wally)

wfloat = wally.astype(float)

r,g,b = wfloat.transpose((2,0,1)) # split into rgb channels, better to use floats

w = wfloat.mean(2) # w is the white channel

pattern = np.ones((24,16),float)

for i in xrange(2):

pattern[i::4] = -1 # build a pattern of +1,+1,-1,-1 on vertical axis -> Wally's shirt.

v = mahotas.convolve(r-w, pattern) # convolve red-white, will give strong response where shirt

mask = (v == v.max())

mask = mahotas.dilate(mask,np.ones((48,24))) # look for max and dilate it to make it visible

wally -= .8*wally * ~mask[:,:,None]

imshow(wally)# imshow(wally)