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RE: imrotate: Differences between Matlab and Octabe
From: |
Journeaux, Ian |
Subject: |
RE: imrotate: Differences between Matlab and Octabe |
Date: |
Sat, 20 Mar 2010 19:32:49 -0500 |
Søren
I very much appreciate you having the opportunity to look at this small
difference.
Is there a way to take advantage of the changes you have made. Do I just ned to
download interp2.m
-----Original Message-----
From: Søren Hauberg [mailto:address@hidden
Sent: Saturday, March 20, 2010 4:28 PM
To: Journeaux, Ian
Cc: address@hidden
Subject: Re: imrotate: Differences between Matlab and Octabe
Hi
Sorry about the late reply
man, 15 03 2010 kl. 09:17 -0500, skrev Journeaux, Ian:
> For our purposes, we were mainly interested in the nearest procedure
> as we want to minimize smoothing of the pixel values in the images.
>
> We observed that the nearest versions of Matlab and Octave are not
> quite the same producing small differences in the results. About half
> (roughly) of Matlab pixels are 1 grey level above that of Octave, the
> rest being equal. This suggests a different way of rounding. The
> central pixel (100,100) where the major shift occurs there is a much
> larger difference - 8 grey levels. In all cases Matlab grey levels are
> exactly where they should be wrt the original image.
>
>
>
> The results for "nearest" are probably good enough for us but since we
> had dug into it, and observed some differences, I though we should
> share the results.
Thanks for sharing this stuff. 'imrotate' simply use the interpolation
function 'interp2', so your results made me look at this function.
The following example illustrates the difference
X = meshgrid (1:4)
interp2 (X, 2.5, 2.5, 'nearest')
In Matlab, this gives me '3', whereas Octave gives '2', which I guess is
the cause of the differences you observed.
I pushed the following changeset
http://hg.savannah.gnu.org/hgweb/octave/rev/62bb59f927b1
which seems to fix this situation.
Søren
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