MATLAB: How to calculate actual snr of image in matlab

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how to calculate actual snr of image in matlab?

Best Answer

Get the signal - that's your "true" noiseless image.

Get the noise - that's your actual noisy image minus the "true" noiseless image.

Divide them element by element, then take the mean over the whole image.

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MATLAB: How can i determine the percentage of noise given the variance of imnoise ?

From the help:

J = imnoise(I,'gaussian',m,v) adds Gaussian white noise of mean m and variance v to the image I. The default is zero mean noise with 0.01 variance.

Let's get the mean of the entire image

meanOfI = mean2(I);

So, on average, I think you're saying you want sqrt(variance) to equal 40% of meanOfI. So now you know what v has to be. Try experimenting around a bit and see what you learn.

Perhaps this demo will be instructive:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
format longg;
format compact;
fontSize = 14;
% Get the original image.
grayImage = imread('eight.tif');
subplot(2, 2, 1);
imshow(grayImage);
title('Original Gray Scale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Add Gaussian noise to the pixel values.
noisyImage = imnoise(grayImage,'gaussian', 0, 0.02);
subplot(2, 2, 2);
imshow(noisyImage, []);
title('Noisy Image', 'FontSize', fontSize);
% Get the noise alone.
noiseOnly = single(noisyImage) - single(grayImage);
subplot(2, 2, 3);
imshow(noiseOnly, []);
title('Image of Only the Noise', 'FontSize', fontSize);
% Calculate the signal to noise ratio
snrImage = abs(noiseOnly) ./ double(grayImage);
subplot(2, 2, 4);
imshow(snrImage, []);
title('Image of the Signal-to-Noise Ratio', 'FontSize', fontSize);
% Get the mean SNR
snrMean = mean2(snrImage);
message = sprintf('The mean Signal-to-Noise Ratio = %.2f', snrMean);
uiwait(msgbox(message));

MATLAB: How to calculate signal to noise ratio of color image

I would not say that. Why do you think the mean gray level of the image is the true signal? It may be for some pixels, but for other pixels, that are supposed to be bright or dark, the signal is not the mean. You need to get the signal and the noise. If you don't have that then you need to make assumptions, like the true signal is the average of pixels in a 3 by 3 window around the pixel and the noise is the standard deviation in that window. So you'll have a mean image (like you can get with conv2()) and a standard deviation image (which you can get with stdfilt()). Then divide the images to get the SNR on a pixel by pixel basis and then take the average of all those values.

Best Answer

Related Solutions

MATLAB: How can i determine the percentage of noise given the variance of imnoise ?

MATLAB: How to calculate signal to noise ratio of color image

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