Path: news.mathworks.com!not-for-mail
From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Embedded Image Resizing using FFT
Date: Thu, 20 Nov 2008 22:25:02 +0000 (UTC)
Organization: The MathWorks, Inc.
Lines: 25
Message-ID: <gg4o3u$qfh$1@fred.mathworks.com>
References: <gg4co5$2cu$1@fred.mathworks.com> <gg4jc2$bck$1@fred.mathworks.com> <gg4kn6$2va$1@fred.mathworks.com> <gg4mdj$sjg$1@fred.mathworks.com>
Reply-To: <HIDDEN>
NNTP-Posting-Host: webapp-02-blr.mathworks.com
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Trace: fred.mathworks.com 1227219902 27121 172.30.248.37 (20 Nov 2008 22:25:02 GMT)
X-Complaints-To: news@mathworks.com
NNTP-Posting-Date: Thu, 20 Nov 2008 22:25:02 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 1300181
Xref: news.mathworks.com comp.soft-sys.matlab:502169


"Matt" <mjacobson.removethis@xorantech.com> wrote in message <gg4mdj$sjg$1@fred.mathworks.com>...
> 
> > > Presumably the method exploits the property that  f(a*t) Fourier transforms into
> > > F(w/a)/|a|.
> > > 
> > > However, I can't see why this would be better than resizing in the non-Fourier domain. You end up doing this same operation, pretty much, in either domain.
> > > 
> > 
> > Performance for one, instead of using bicubic or bilineair transforms on the image you should be able to resize the image using i.e. a lowpass filter to make the image smaller and add zero-padding to make the image larger (or so I've read). 
> 
> I don't really follow that. Lowpass filtering an image will make it smoother, not smaller.
> 
> Zero-padding in frequency space will cause the image to be upsampled by sinc-interpolation. You could then use these upsamplings to resize your image.
>  
> However, it would give you many more interpolated samples than you need and than you would use if you just re-interpolated the image directly in image space using say, interp2(). I can't see how that ends up being more efficient.
> 
> 
> > What technique would you suggest to resize an image in the Embedded Matlab Subset? 
> 
> I don't see why you wouldn't just write your own fast interp2.c function and use that...

This was my source for the lowpass comment:
http://www.watermarkingworld.org/WMMLArchive/0302/msg00055.html

I haven't got a clue how to use the interp2() function to resize an image and certainly not in C.