Write a function to add random noise to an image in matlab

How do I create a function to add random noise without using imnoise? I am trying to figure out how to do it without using the built-in matlab functions. I know I have to add a random integer to every pixel...

function output=randomnoise(current_img)
for current_img(n)
    current_img(n)=current_img(n)+ randi([-255 255],1)
    n=n+1
end

This is what I am coming up with right now, but I don't think my loop is visiting each value. How do I visit each pixel and how do I add random noise to it?

[Walter Roberson]

The distribution of random value you add to the pixel is important.

Answer 1

[Image Analyst]

Try this:

function output=randomnoise(current_img)
% Cast to double;
current_img = double(current_img);
[rows, columns] = size(current_img)
for col = 1 : columns
    for row = 1 : rows
        output(row, col) = current_img(row, col)+ randi([-255 255],1)
    end
end

Or you could do away the the two loops and just vectorize it

noise = randi([-255, 255], rows, columns);
output = current_img + noise;

Answer 2

[Walter Roberson]

http://www.mathworks.com/help/matlab/ref/for.html

Answer 3

[Arifaa A]

function output=randomnoise(current_img)
% Cast to double;
current_img = double(current_img);
[rows, columns] = size(current_img)
for col = 1 : columns
    for row = 1 : rows
        output(row, col) = current_img(row, col)+ randi([-255 255],1)
    end
end

noise = randi([-255, 255], rows, columns);
output = current_img + noise;

[Image Analyst]

How is that different than my code? It looks identical.