PSNR.py

import numpy as np
import math
import cv2

def Representational(r,g,b):
	return (0.299*r+0.287*g+0.114*b)

def calculate(img):
	b,g,r = cv2.split(img)
	pixelAt = Representational(r,g,b)
	return pixelAt

def main():
	
	#Loading images (orignal image and compressed image)
	orignal_image = cv2.imread('orignal_image.png',1)
	compressed_image = cv2.imread('compressed_image.png',1)

	#Getting image height and width
	height,width = orignal_image.shape[:2]

	orignalPixelAt = calculate(orignal_image)
	compressedPixelAt = calculate(compressed_image)

	diff = orignalPixelAt - compressedPixelAt
	error = np.sum(np.abs(diff) ** 2)

	error = error/(height*width)

	#MSR = error_sum/(height*width)
	PSNR = -(10*math.log10(error/(255*255)))

	print("PSNR value is {}".format(PSNR))


if __name__ == '__main__':
	main()