| Re: Image processing question [message #10211] |
Tue, 28 October 1997 00:00 |
pit
Messages: 92
Registered: January 1996
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Member |
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In article <01bce2f7$500510c0$181b8581@51peg>,
"Eric Williams" <eric@astro.wesleyan.edu> writes:
> Hello,
>
> This might not be specific to IDL, but I am using IDL for this work so
> I thought I would ask the experts. I am looking for a reference or
> source to read up on processes for combining a series of images. The
> images will need to be shifted to match up objects (specifically
> stars) and use the best algorithmn to do the adding. This is a common
> procedure in astronomy, but I haven't found any "instructional"
> material that explains the possible options to perform this operation.
> Of course if anyone has written code that already does this I would
> be interested in checking it out.
Hi Eric,
I'm using this kind of adding images in my Speckle Code. It can be used
either automatic (when you know where approximately to insert the new
part) or manually.
First, you define an empty image I of approx. the size of the result, and
a weighting array(float) W of the same size.
To add a part, you multiply the partial image with a cosine-like
weighting function and add it at the apropriate position to the
resulting image, and add the weighting function to the weight array.
The final image will be F/W
To find the position of a new part, you have to find the indices of the
overlap of the up-to-then added image and the new part. Then you use
the standard deviation of the difference in that overlap as a measure of
the position: You have to find the minimum value for the stdev.
So you start at some reasonable position, and compute the stdev for that
point and the 8 surrounding ones. Go to the position with minimal stdev
and recycle until you are at the minimum. This gives you the position
where to insert the new part.
If you (or someone else) is interested in the code I can extract the
functions from my code and put them on a FTP-Server.
Peter
--
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~
Peter "Pit" Suetterlin http://www.uni-sw.gwdg.de/~pit
Universitaets-Sternwarte Goettingen
Tel.: +49 551 39-5048 pit@uni-sw.gwdg.de
-- * -- * ...-- * -- * ...-- * -- * ...-- * -- * ...-- * -- * ...-- * --
Come and see the stars! http://www.kis.uni-freiburg.de/~ps/SFB
Sternfreunde Breisgau e.V. Tel.: +49 7641 3492
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