HISTEQ default not consistent with syntax?

If I have an 8-bit image IM (e.g. cameraman.tif), why does histeq(IM) produce a different result than histeq(IM,ones(1,256))??

Shouldn't they be identical? The description says hgram defaults to ones(1,n)*prod(size(A))/n. Since cameraman is 256x256 and n=2^8, shouldn't it scale normally?

Answer 1

[Matt Fig]

IM = imread('cameraman.tif');
I = histeq(IM);
I2 = histeq(IM,ones(1,64)*(numel(IM)/64));
isequal(I,I2)

ans =

       1

[Jurgen]

I see it uses n=64 then, I was testing with n=256. Because of the description I was under the impression that n=length(HGRAM). Thanks for clearing that up.