Calculating UACI, NPCR for 2 images

Question

LOKESH 2012-4-22

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/36171-calculating-uaci-npcr-for-2-images

评论： Walter Roberson 2021-5-25

Presently I have a problem in implementing the UACI and PSNR code for 2 images which are respectively Original & Cipher Images. I need the code for calculating it......

What would the Code? I don't have much idea about it.. Do I need to find UACI between 2 images or only 1 image will be sufficient

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Answer 1

Image Analyst 2012-4-22

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https://ww2.mathworks.cn/matlabcentral/answers/36171-calculating-uaci-npcr-for-2-images#answer_45266

在 MATLAB Online 中打开

See my demo:

% Demo to calculate PSNR of a gray scale image.
% http://en.wikipedia.org/wiki/PSNR
% by ImageAnalyst 
clc; 
close all; 
clearvars; 
workspace;
% Read in standard MATLAB demo image.
grayImage = imread('cameraman.tif');
[rows columns] = size(grayImage);
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grey Scale Image');
set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.
% Add noise to it.
noisyImage = imnoise(grayImage, 'gaussian', 0, 0.003);
subplot(2, 2, 2);
imshow(noisyImage, []);
title('Noisy Image');
% Calculate mean square error.
mseImage = (double(grayImage) - double(noisyImage)) .^ 2;
subplot(2, 2, 3);
imshow(mseImage, []);
title('MSE Image');
mse = sum(sum(mseImage)) / (rows * columns);
% Calculate PSNR (Peak Signal to noise ratio).
PSNR = 10 * log10( 256^2 / mse);
message = sprintf('The mean square error is %.2f\nThe PSNR = %.2f', ...
  mse, PSNR);
msgbox(message);
% set(gcf, 'Position', get(0,'Screensize')); % Maximize figure.

After this example you should be able to use similar code to easily calculate NPCR and UACI, according to http://www.cyberjournals.com/Papers/Apr2011/05.pdf. You need both images to calculate them since they are a measure of the differences between the two images.

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Komeil 2016-10-20

The NPCR is different from the PSNR.

Walter Roberson 2016-10-20

Image Analyst says "After this example you should be able to use similar code to easily calculate NPCR" -- in other words, he has not given the code here, but he has given a framework that can be adapted to calculate NPCR by anyone who looks up the formula for NPCR.

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Answer 2

Hyderkkk 2020-8-31

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/36171-calculating-uaci-npcr-for-2-images#answer_487220

How do i get the NPCR and UACI of an original speech and encryption in matlab code ?

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Image Analyst 2021-5-25

I have no idea. Who said uaci should always be about 33?

Walter Roberson 2021-5-25

This file give the relation between two encrypted images of same size and type but I need the relation between original speech and encrypted speech

Are you familiar with the encryption technique that is often called ROT13? It is a caeser cypher in which each letter in the first half of the alphabet is replaced with the letter in the corresponding position in the second half of the alphabet, and vice versa, so 'A' gets replaced with the character 13 further on (which is 'N'), and 'p' would get replaced with the character 13 earlier (which is 'c')

Now take the original image, and apply ROT13 to it. Then take the result, and apply ROT13 to that, for even stronger encryption.

Now take the relationship between that double-ROT13 encrypted image and the encryption you found using a different method. As they are both encrypted image, there should be no problem comparing the two using an algorithm that compares encrypted images, right?

... But it turns out that applying ROT13 twice always gets you back exactly the original data. Therefore the original data is itself an encrypted version of the original data... just encrypted with a very weak encryption. And so you can use your algorithm that compares two encrypted images in order to compare the original image to the version of it you encrypted some other way than double-ROT13.

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