Undefined mat2gray

[Olli Alatalo]

I've got the following piece of code

function A=noise(i, j)
A=round(unifrnd(0,255,i,j));
B=mat2gray(A);
imshow(B);
figure();
imhist(B);
figure();
pause(4);

when I run it, I receive an error:

error: `mat2gray' undefined near line 3 column 3


What? Why? How to fix?