I_gray = imread('logo_gray.tif');

% logo with salt & pepper noise
I_noise = imnoise(I_gray,'salt');

% adding noise only to half the logo
I1st = I_gray(: , 1:round(end/2)-1);
I2nd = I_gray(: , round(end/2):end);
I2nd_noise  = imnoise(I2nd,'salt');

I_noise = [I1st I2nd_noise];

imshow(I_noise)
title('salt & pepper noise')