Path: news.mathworks.com!not-for-mail
From: <HIDDEN>
Newsgroups: comp.soft-sys.matlab
Subject: Re: How to calculate the angle between two images?
Date: Fri, 3 Apr 2009 14:39:01 +0000 (UTC)
Organization: STFC Rutherford Appleton Laboratory
Lines: 29
Message-ID: <gr5725$e6e$1@fred.mathworks.com>
References: <gr4ten$oks$1@fred.mathworks.com> <gr4u55$add$1@fred.mathworks.com> <6dc4d317-8b62-4e03-8bea-662e35f6eb67@d38g2000prn.googlegroups.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 1238769541 14542 172.30.248.37 (3 Apr 2009 14:39:01 GMT)
X-Complaints-To: news@mathworks.com
NNTP-Posting-Date: Fri, 3 Apr 2009 14:39:01 +0000 (UTC)
X-Newsreader: MATLAB Central Newsreader 968489
Xref: news.mathworks.com comp.soft-sys.matlab:530065

Skeptic <skeptic@mailinator.com> wrote in message <6dc4d317-8b62-4e03-8bea-662e35f6eb67@d38g2000prn.googlegroups.com>...
> Dave Robinson wrote a nice algorithm:
> > One method that I found for easily determining the relative
> > angle of 'twist' between a known reference image  and a rotated image was accomplished very reliably even for arbitrary images.
> >
> [snip]
> > Dave Robinson
> -------------------------------------------------------
> Dave:
> Nice.  Clever yet makes good intuitive sense.  Does it still perform
> well under stress conditions such as:
> 1.  image contrasts don't match
> 2. rotations, such as 45 degrees, where some information is rotated
> out and other new info is rotated in (think of an aerial photo rotated
> 45 degrees).
> 3. rotation is not about the center of the image.
> -ImageAnalyst

1) My application had relatively controlled lighting, but as the angle is computed indirectly via a ratio then it should be fairly robust against variable contrast

2) Again this wasn't a problem to me, my 'credit cards' were on a featureless conveyor belt. In general I think you have a good point.

3) The angle of rotation is translation independent, so apart from point 2) where you bring in other image regions you are OK.

Thanks for your welcome input, it is nice to be able to bounce ideas with someone of your reputation

Regards

Dave Robinson