how to use NMI for images

hi every body. I am trying to use nmi.m which is attached below and downloaded from mathworks to calculate normalized mutual information between to images.

x=rgb2gray(imread('a.jpg'));
y=rgb2gray(imread('b.jpg'));
z = nmi(x, y);

but i have this error:

Error using sparse

Index into matrix must be an integer.

Error in nmi (line 19)

Mx = sparse(idx,x,1,n,k,n);

could anyone solve this error for me?

[Walter Roberson]

After you create x and y, please show class(x) and class(y), and also min(unique(diff([x(:);y(:)])))

[talayeh ghodsi]

hello sir, thanks for your respond. you mean this?

x=rgb2gray(imread('a.jpg'));
y=rgb2gray(imread('b.jpg'));
class(x)
class(y)
min(unique(diff([x(:);y(:)])))
z = nmi(x, y);

the class of x and y is uint8

[Walter Roberson]

What showed up for

 min(unique(diff([x(:);y(:)])))

?

Also please show min(x(:)), max(x(:))

[talayeh ghodsi]

> min(unique(diff([x(:);y(:)])))

ans =

uint8

0

> min(x(:)), max(x(:))

ans =

uint8

0

ans =

uint8

255

[Walter Roberson]

Replace

x = x-l+1;
y = y-l+1;

with

x = double(x-l+1);
y = double(y-l+1);

[talayeh ghodsi]

thanks sir it works well