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Add salt and pepper noise to image

How to add salt and pepper noise to an image


          To obtain an image with ‘speckle’ or ‘salt and pepper’ noise we need to add white and black pixels randomly in the image matrix.



First convert the RGB image into grayscale image.
Then generate random values for the size of the matrix.
Here I used MATLAB function ‘randint’.





This function will generate random values for the given matrix size within the specified range.
For instance, consider an image matrix of size 4X3


Imgmatrix =
   237   107   166
   234    95   162
   239   116   169
   56   126    89


Generate random values for a 4X3 matrix with range 0 to 10.
randint(4,3,[0,10])

ans =
     4    10     4
     7     8     4
    10     0     5
     3    10     9

    

Now we can replace with pixel value zero (black) in the image matrix if there is ‘0’ value in the random matrix.

Now the image matrix will have black pixels.

Imgmatrix =
   237   107   166
   234    95   162
   239   0   169
   56   126    89


 
Similarly, replace the image matrix pixel value with ‘255’ if there is value ‘10’ in the random matrix.
The white pixels are now added.

Imgmatrix =
   237   255   166
   234    95   162
   255   0   169
   56   126    89

Black=0 white=255

 

MATLAB CODE:


A=imread('taj.jpg');
B=rgb2gray(A);


black=3;
white=253;
%Adjust the values in 'black' and 'white' to increase the noise.

NoiseImg = B;
    Rmatrix = randint(size(B,1),size(B,2),[0,255]);
    NoiseImg(Rmatrix <= black) = 0;
    NoiseImg(Rmatrix >=white) = 255;
    RImg=medfilt2(NoiseImg);
    figure,subplot(1,2,1),imshow(NoiseImg),title('Add ''Salt and Pepper'' Noise');
    subplot(1,2,2),imshow(RImg),title('After Noise Removal');






 I used the MATLAB function 'medfilt2' to remove noise. 


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7 comments:

Mukesh Mann said... Reply to comment

how to add different percentage level of noise to an image

Aaron Angel said... Reply to comment

@Mukesh Mann
Try this code.
B=imread('eight.tif');
%if Pa==Pb;
percen=20;
%Noise level 20
Prob_den_f=255*percen/100;
NoiseImg = B;
Rmatrix = randint(size(B,1),size(B,2),[0,255]);
NoiseImg(Rmatrix <=Prob_den_f/2) = 0;
NoiseImg(Rmatrix >Prob_den_f/2&Rmatrix<Prob_den_f) = 255;
RImg=medfilt2(NoiseImg);

Mukesh Mann said... Reply to comment

@Aaron Angelthanks a lot angel....can we apply the following code to add different noise to an inmage
let standard deviation 0.25
then
types of noise
1.noise_spekle=imnoise(image,'speckle',.25);
2. noise_gaussian=imnoise(image,'gaussian',.25);
3. noise_salt&pepper=imnoise(image,'salt&pepper',.25);

would it means that we had addded 25% of different types of noise to an image ??

Mukesh Mann said... Reply to comment

thanks budddy

pranab chowdhury said... Reply to comment

what are the difference between salt and pepper noise and gaussian noise? and what are the Matlab codes to add both noises separately to an ECG signal? please help.

Satrughan Kumar said... Reply to comment

How to add RVIN

Megastar said... Reply to comment

why u have to add salt and pepper noise to image?

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