how can i find local histogram equalization ?

how can i find local histogram?

i used this code but it gives an error

i= imread('braiin.png');

ff=im2double(i);

w=input('\nEnter the Neighborhood or Window size : ');

k=input('\nEnter the value of the constant k (value should be between 0 and 1) : ');

M=mean2(ff);

z=colfilt(ff,[w w],'sliding',@std);

m=colfilt(ff,[w w],'sliding',@mean);

A=k*M./z;

g=A.*(ff-m)+m;

sublpot(1,2,1)

imshow(g);

this is the error:

Error using >=

Matrix dimensions must agree.

Error in colfilt (line 134)

if all(block>=size(a)), % Process

the whole matrix at once.

Error in Untitled22 (line 27)

z=colfilt(ff,[w w],'sliding',@std);

any other suggested soulution?thanks