```
Subject: Re: t-distribution display (histogram) with spm99b
From: john@fil.ion.ucl.ac.uk (John Ashburner)
Date: Fri, 30 Jul 1999 14:06:20 +0100
To: spm@mailbase.ac.uk, jovicich@humc.edu
The attached program should produce the histograms you are after. To
call it, type:
V = spm_vol(spm_get(1,'*.img','Select image...'));
[n, x] = histvol(V, 100);
figure;
bar(x,n);
```

[…]

```
Regards,
-John
```

The attached function is here histvol.m and below

```
function [n, x]=histvol(V, nbins)
% Create Histogram of an image volume
% FORMAT [n, x]=histvol(V, nbins)
% V - mapped image volume (see spm_vol)
% nbins - number of bins to use.
% n - number of counts in each bin
% x - position of bin centres
%_______________________________________________________________________
% @(#)JohnsGems.html 1.42 05/02/02
if nargin==1, nbins = 256; end;
% determine range...
mx = -Inf;
mn = Inf;
for p=1:V.dim(3),
img = spm_slice_vol(V,spm_matrix([0 0 p]),V.dim(1:2),1);
msk = find(isfinite(img));
mx = max([max(img(msk)) mx]);
mn = min([min(img(msk)) mn]);
end;
% compute histograms...
x = [mn:(mx-mn+1)/nbins:mx];
n = zeros(size(x));
for p=1:V.dim(3),
img = spm_slice_vol(V,spm_matrix([0 0 p]),V.dim(1:2),1);
msk = find(isfinite(img));
n = n+hist(img(msk),x);
end;
return;
```