| Re: particle detection - a way to speed up things? [message #57076 is a reply to message #56936] |
Fri, 30 November 2007 00:22  |
Ingo von Borstel
Messages: 54
Registered: September 2006
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Member |
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Hi,
>
> If I'm reading your program correctly, you have a big image consisting
> (presumably) of
> a lot of empty space and numerous particles that you have identified
> in some way.
Yes, correct. Black image with an arbitrary amount (<= 1000) of small
blobs with a value different than zero; those blobs numbered using
either label_region or watershed.
> My guess is that the main reason your program is slow is that for each
> particle you
> are summing over the entire image.
Probably. Half the time is consumed by the determination of the position
for each particle in the overall image.
> I can see two ways to speed things up:
> 1) Create subsets of the image for each particle and only sum only
> over the subset containing the particle.
In order to calculate the absolute position of a particle, I need to
know where on an image it resides. I think I'll loose this information
with this approach.
> 2) Use something like HISTOGRAM or a multi-dimensional historgam with
> the REVERSE_INDICES keyword (or equivalent)
> to get the indices associated with each particle and sum over those.
> The histogram command would be applied to your
> particle_image field with a binsize of 1 and starting at 0. See
> http://www.dfanning.com/tips/histogram_tutorial.html
> for ideas on how to approach this problem using histograms.
The latter might have potential. I'll give it a try and report back then.
Thanks a lot for your input.
Cheers,
Ingo
--
Ingo von Borstel <newsgroups@planetmaker.de>
Public Key: http://www.planetmaker.de/ingo.asc
If you need an urgent reply, replace newsgroups by vgap.
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