Image processing Gaussian noise

I need to add gaussian noise on a gray image. But i need to do it without using library.

I will be glad if you help me.

[Image Analyst]

Can you at least use randn()? Or if not, can you use rand()? Or do you have to write your own random number generator?

Answer 1

[DGM]

Something like this:

% same as imnoise() defaults
gaumean = 0;
gauvar = 0.01;

inpict = imread('cameraman.tif');
outpict = im2uint8(im2double(inpict) + gaumean + sqrt(gauvar)*randn(size(inpict)));

montage({inpict,outpict})

Note that this example assumes that the intended output class is uint8. Adjust as needed.

Answer 2

[yanqi liu]

clc;clear all;close all;
img = mat2gray(imread('rice.png'));
img2 = img+0.1*randn(size(img),'like',img);
figure;
subplot(1,2,1); imshow(mat2gray(img));
subplot(1,2,2); imshow(mat2gray(img2));

[DGM]

Using mat2gray() as a general tool for converting images to floating point alters the relative scaling of the information, whereas the intended tools (e.g. im2double) scale things with respect to the limits implied by the class (see getrangefromclass()). It increases contrast unnecessarily. It's easier to notice with a lower-contrast image:

img = imread('pout.tif'); % original image
imshow(img);

img2 = mat2gray(img); % this stretches the contrast 
img2 = img2 + 0.1*randn(size(img2),'like',img2);
figure; imshow(img2);

img3 = im2double(img); % this doesn't change the contrast
img3 = img3 + 0.1*randn(size(img3),'like',img3);
figure; imshow(img3);