"""
	Peak signal-to-noise ratio - PSNR - https://en.wikipedia.org/wiki/Peak_signal-to-noise_ratio
 Soruce: https://tutorials.techonical.com/how-to-calculate-psnr-value-of-two-images-using-python/
"""

import math
import os

import cv2
import numpy as np

def psnr(original, contrast):
 mse = np.mean((original - contrast) ** 2)
 if mse == 0:
 return 100
 PIXEL_MAX = 255.0
 PSNR = 20 * math.log10(PIXEL_MAX / math.sqrt(mse))
 return PSNR


def main():
 dir_path = os.path.dirname(os.path.realpath(__file__))
 # Loading images (original image and compressed image)
 original = cv2.imread(os.path.join(dir_path, 'original_image.png'))
 contrast = cv2.imread(os.path.join(dir_path, 'compressed_image.png'), 1)

 original2 = cv2.imread(os.path.join(dir_path, 'PSNR-example-base.png'))
 contrast2 = cv2.imread(os.path.join(dir_path, 'PSNR-example-comp-10.jpg'), 1)

 # Value expected: 29.73dB
 print("-- First Test --")
 print(f"PSNR value is {psnr(original, contrast)} dB")

 # # Value expected: 31.53dB (Wikipedia Example)
 print("\n-- Second Test --")
 print(f"PSNR value is {psnr(original2, contrast2)} dB")


if __name__ == '__main__':
 main()