Python + OpenCV: create negative image

Example to generate negative image:

import sys
import cv2

print("Python version: \n" + sys.version)
print("cv2 version: " + cv2.__version__)

#img1 and img2 must be in same size
img1 = cv2.imread('Raspberry_Pi_Logo.png', 1)
img2 = (255-img1)

cv2.imshow('img1',img1)
cv2.imshow('img2',img2)

cv2.waitKey(0)
cv2.destroyAllWindow()

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Edit the example "Capture Raspberry Pi Camera image, display on OpenCV, Matplotlib PyPlot and Tkinter GUI" to generate negative image from the picamera captured image.

import picamera
import picamera.array
import time
import cv2
from matplotlib import pyplot as plt
import Tkinter 
import Image, ImageTk
import sys

def capturePiCam():
    with picamera.PiCamera() as camera:
        cap=picamera.array.PiRGBArray(camera)
        camera.resolution = (640, 480)
        camera.start_preview()
        time.sleep(3)
        camera.capture(cap,format="bgr")
        global img
        img =cap.array
        img = (255-img)

#- display on OpenCV window -
def displayAtOpenCV():
    cv2.namedWindow('imageWindow', cv2.WINDOW_AUTOSIZE)
    cv2.imshow('imageWindow',img)
    cv2.waitKey(0)
    cv2.destroyAllWindows()

#- display with matplotlib -
def displayAtPyplot():
    plt.figure().canvas.set_window_title("Hello Raspberry Pi")
    plt.imshow(cv2.cvtColor(img, cv2.COLOR_BGR2RGB))
    plt.xticks([]), plt.yticks([])  # to hide tick values on X and Y axis
    plt.show()
    
#- display on Tkinter -
def displayAtThinter():
    root = Tkinter.Tk() 
    b,g,r = cv2.split(img) 
    img2 = cv2.merge((r,g,b))
    img2FromArray = Image.fromarray(img2)
    imgtk = ImageTk.PhotoImage(image=img2FromArray) 
    Tkinter.Label(root, image=imgtk).pack() 
    root.mainloop()

def displayUsage():
    print("usage: ")
    print("python pyCV_picam.py 1 - display wiyh OpenCV window")
    print("python pyCV_picam.py 2 - display with matplotlib")
    print("python pyCV_picam.py 3 - display with Tkinter")

if len(sys.argv) != 2:
    displayUsage()
    sys.exit()
    
opt = sys.argv[1]

if opt=="1":
    print("display wiyh OpenCV window")
    capturePiCam()
    displayAtOpenCV()
elif opt=="2":
    print("display with matplotlib")
    capturePiCam()
    displayAtPyplot()
elif opt=="3":
    print("display with Tkinter")
    capturePiCam()
    displayAtThinter()
else:
    displayUsage()