An error while finding standart deviation of an image in MATLAB : [enter image description here][1]


  [1]: https://i.stack.imgur.com/Gz89O.jpg

Hi,
firstly i want to find standart deviation of this image. 
Secondly i want to find standart deviation of all lines in this image.

But, at the first step somethings going wrong and i see this fault. 

        >> A = imread('C:\Users\PC\Desktop\deneme.jpg');
        >> std (A);
        Error using var (line 65)
        First argument must be single or double.

        Error in std (line 38)
        y = sqrt(var(varargin{:}));

line 65: error(message('MATLAB:var:integerClass'));
line 38: y = sqrt(var(varargin{:}));

How can i solve this problem and what is the code of finding standart deviation of all lines in this image.

Thank you.