matlab - calculating standard deviation results index exceeds matrix dimention error -

i calculating standard deviation of 250x250 image getting following error can please..

  210.2683 ??? index exceeds matrix dimensions. error in ==> test @ 5 std1=std(g(:));

my code snippet is

  kl=imread('ai427.jpg');   g=rgb2gray(kl);   m=mean(g(:));   disp(m)   std1=std(g(:));   disp(std1)

i dont know error , how resolve it(i mean how result )

any appreciated.....

first, convert image double,

  g=double(rgb2gray(kl));

then check haven't used word std before user variable or function, or add clear std before line , see if helps.

SoEM