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Quantitatively check the quality of a compressed image by calculating the Structural Similarity Index (SSIM) and Mean Square Errors (MSE) between two images.
#!/usr/bin/env python
from skimage.metrics import structural_similarity as ssim
import numpy as np
import cv2
import argparse
def options():
parser = argparse.ArgumentParser(description="Read image metadata")
parser.add_argument("-o", "--first", help="Input image file.", required=True)
parser.add_argument("-c", "--second", help="Input image file.", required=True)
args = parser.parse_args()
return args
def mse(imageA, imageB):
# the 'Mean Squared Error' between the two images is the sum of the squared difference between the two images
mse_error = np.sum((imageA.astype("float") - imageB.astype("float")) ** 2)
mse_error /= float(imageA.shape[0] * imageA.shape[1])
# return the MSE. The lower the error, the more "similar" the two images are.
return mse_error
def compare(imageA, imageB):
# Calculate the MSE and SSIM
m = mse(imageA, imageB)
s = ssim(imageA, imageB)
# Return the SSIM. The higher the value, the more "similar" the two images are.
return s
def main():
# Get options
args = options()
# Import images
image1 = cv2.imread(args.first)
image2 = cv2.imread(args.second, 1)
# Convert the images to grayscale
gray1 = cv2.cvtColor(image1, cv2.COLOR_BGR2GRAY)
gray2 = cv2.cvtColor(image2, cv2.COLOR_BGR2GRAY)
# Check for same size and ratio and report accordingly
ho, wo, _ = image1.shape
hc, wc, _ = image2.shape
ratio_orig = ho/wo
ratio_comp = hc/wc
dim = (wc, hc)
if round(ratio_orig, 2) != round(ratio_comp, 2):
print("\nImages not of the same dimension. Check input.")
exit()
# Resize first image if the second image is smaller
elif ho > hc and wo > wc:
print("\nResizing original image for analysis...")
gray1 = cv2.resize(gray1, dim)
elif ho < hc and wo < wc:
print("\nCompressed image has a larger dimension than the original. Check input.")
exit()
if round(ratio_orig, 2) == round(ratio_comp, 2):
mse_value = mse(gray1, gray2)
ssim_value = compare(gray1, gray2)
print("MSE:", mse_value)
print("SSIM:", ssim_value)
if __name__ == '__main__':
main()
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