Problem to add gaussian noise to image

I should add gaussian noise with standard deviation = 25 to the 'zebre.y' (attached) image. I use this code

clear all;close all;clc;

f=fopen('zebre.y','r');
x=fread(f,[321 481],'uint8');
x=double(x');
fclose(f);
figure();imshow(x,[]);

%x=1+(1/(min(min(x))-max(max(x)))).*(x-min(min(x)));
x_noisy=imnoise(x,'gaussian',0,5);
figure();imshow(x_noisy,[]);

but the problem is that the noisy image show only noise, and not the original image with noise added. I tried to scale the image to [0 1] to, but the result is not different. Where is my mistake?

Answer 1

[Image Analyst]

Well you messed up. Look at my code to see how to do it correctly:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures if you have the Image Processing Toolbox.
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 22;

% Read in a standard MATLAB color demo image.
folder = 'C:\Users\diul\Documents\Temporary';
baseFileName = 'zebre.y';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % Didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end

fileID = fopen(fullFileName, 'r');
uint8Image = fread(fileID,[481 321],'*uint8');
fclose(fileID);
% Display the original uint8  image.
subplot(2, 2, 1);
imshow(uint8Image,[]);
axis on;
title('Original uint8 Image', 'FontSize', fontSize);

% Add noise to the uing8 image.
noisyImage8 = imnoise(uint8Image, 'gaussian', 0, 0.05);
% Display the noisy uint8  image.
subplot(2, 2, 3);
imshow(noisyImage8,[]);
axis on;
title('Noisy uint8 Image', 'FontSize', fontSize);

% Convert to double.
dblImage = im2double(uint8Image');

% Display the double image.
subplot(2, 2, 2);
imshow(dblImage,[]);
axis on;
title('Original Double Image', 'FontSize', fontSize);
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows, columns, numberOfColorBands] = size(dblImage);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);

% Normalize image to the range 0-1
minGL = min(dblImage(:));
maxGL = max(dblImage(:));
dblImage = (dblImage-minGL) / (maxGL-minGL);
noisyImage = imnoise(dblImage, 'gaussian', 0, 0.05);
% Check to see that it did it correctly.
minGL = min(dblImage(:))
maxGL = max(dblImage(:))
subplot(2, 2, 4);
imshow(noisyImage, []);
title('Noisy Double Image', 'FontSize', fontSize);

[Image Analyst]

diul's "Answer" moved here:

Thanks a lot. From your code I can see where my faults are. 1)Image dimensions, but those are given, so I take that on trust 2)The difference that allow me to add Gaussian noise in right way is that '*' before 'uint8'

I will be very thankful if you can explain me the difference between 'uint8' and '*uint8'

[Image Analyst]

*uint8 will give you a uint8 output. uint8 will give you a double output, as described in the help. Can you mark the Answer as Accepted?

[Raghhav Dev]

Why you used 0.05 var if you need to add noise of 25 sd? I am getting problem to add noise with different sd.

[Image Analyst]

You need to add the variance assuming your image is in the range 0-1, not 0-255.

[Deepa Abraham]

variance,v =(sigma/255)^2; Is this right?