# IMAGE PROCESSING

" Two roads diverged in a wood, and I,
I took the one less traveled by,
And that has made all the difference "-Robert Frost

### 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:

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);
subplot(1,2,2),imshow(RImg),title('After Noise Removal');

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

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Mukesh Mann said...

how to add different percentage level of noise to an image

Aaron Angel said...

@Mukesh Mann
Try this code.
%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...

@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...

thanks budddy

pranab chowdhury said...

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...