MATLAB: The value of variance in function imnoise in case of gaussian is a bit confusing

gaussianImage Processing Toolboximnoisevariance

Hi Everyone,

I am trying to add gaussian noise to image with some variance and mean, generally variance of 50 is considerable, but the function imnoise make image so much noisy even for a variance of 0.1,

image = rgb2gray(imread('pepper.jpg')); noisy_image = imnoise(image,'gaussian',0,0.1);

I just wanna ask that is this variance normalized using any specific scale, if yes, then with what factor do I need to multiply it to get the original one.

Best Answer

imnoise works with an intensity image, so if you are inputting a unit8 image for example with values in the range [0,255], then imnoise first does

 I = imread('eight.tif');
 I = im2double(I);

before adding the Gaussian noise, so basically you scale every value in your image [0,255] by 255 so that it falls into the interval [0,1] and then add the noise to that.

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MATLAB: Read and display RGB png/jpg image

You png file is actually an indexed image with a colormap. You can see it in color using following statements

[img, map] = imread('image.png');
imshow(img, map)

or, you convert it to rgb, you can use ind2rgb()

[img, map] = imread('image.png');
img_rgb = ind2rgb(img, map);
imshow(img_rgb)

MATLAB: Failed to add uniform noise to the image

Hi. You don't need imnoise:

round(128+0.2)=128

with 0.1 and 0.2 like you didn't add any noise. Uniform noise with zero mean:

image = ones([512,512])*128;
A = -30;
B = 30;
matrix_uniform = A + (B-A)*rand(size(image));
noisy_image = image + matrix_uniform;
figure,
subplot(1,2,1)
imshow(noisy_image./255), 
subplot(1,2,2)
imhist(uint8(noisy_image))

Best Answer

Related Solutions

MATLAB: Read and display RGB png/jpg image

MATLAB: Failed to add uniform noise to the image

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