Re: how to calculate histogram using one for loop

On 17 Okt, 11:05, "Jamal Mohamed" <in.ja...@xxxxxxxxx> wrote:
hi everybody

already i calculated  histogram for a image like following code [ only calculation part]
[row, col] =size(I);
h = zeros(256, 1);
for i=1:row
for j=1:col
Z=I(i,j);           % I is image
h(Z+1)=h(Z+1)+1;
end
end

The above is the conceptually correct solution.

my question is how to calculate histogram using one for loop

You can exploit the fact that matlab stores the image
as a NxM continuous block of memory, and write something
like

II = I(:);

Now II is a N*M x 1 vector. But do note that there is
nothing to gain by this:

1) II has to be allocated in memoy
2) The data has to be transferred from I to II
3) II takes as much space as I

So this approach requires twice the memory footprint
and requires several times as much time the method you
already use. There is no reason why you would want to
do this as just one loop.

Rune
.

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