#! /usr/bin/env python
# -*- coding: utf-8 -*-

import numpy as np
import cv2

width  = 320
height = 240
margin =  50

cap = cv2.VideoCapture(0)

# Let us resize the video to width x height
cap.set(3,width)
cap.set(4,height)

# Processing starts
while(True):
    is_ok, frame  = cap.read()
    subframe      = frame[margin:(height-margin), # row number on first axis.
                          margin:(width-margin),  # column number on second axis.
                          :]                      # channel number (R,G or B) on third axis.
    # subframe    = 255 - subframe                # ask why this is wrong...
    subframe[...] = 255 - subframe
    cv2.imshow('display',frame)
    if cv2.waitKey(1) & 0xFF == 27: #27 is the ascii for escape
        break

# When everything done, release the capture
cap.release()
cv2.destroyAllWindows()