[Insight-users] Criterion to stop 1+1_evolutionary optimizer?

[Stephen R. Aylward]

I am glad you're making use of the flexibility of itk by having multiple optimizers.   It would make a nice article for the upcoming insight software journal to evaluate the different configurations..I think the performance improvement that you credit the pyramid scheme is (aside from speed) equivalent to simplifying the metric space via blurring in image space inducing a blurring (high freq feature/noise removal) in metric space...it would be interesting to see if that did or didn't equate to reducing local extremes and if a relationship could be quantified between scale of confounding (non corresponding) image features and local extremes in metric space...

Until then..multiple options is great :)...

s

-----Original Message-----

From:  "Li, George (NIH/NCI)" <ligeorge at mail.nih.gov>
Subj:  RE: [Insight-users] Criterion to stop 1+1_evolutionary optimizer?
Date:  Thu Mar 17, 2005 10:16 am
Size:  4K
To:  "'Stephen R. Aylward'" <aylward at unc.edu>
cc:  "'Luis Ibanez'" <luis.ibanez at kitware.com>,   "'Insight-users at itk.org'" <Insight-users at itk.org>

Stephen,

Thanks for the input. I am using Mattes method
As it is a smoother metric, as you said. I have
Made an option in my program for users to choose 
Either the evolutionary optimizer or the regular
Step optimizer. Just for sake of code integrity, 
I would like to have both done in the same fashion. 

On the other hand, I would think that the multi-
Resolution strategy is not completely parallel 
To what the evolutionary Optimizer does. The 
Former is built mostly from performance concern
And avoiding local extremes may be a by-product,
While latter is one of the best optimizers in 
Terms of avoiding local traps and tolerating 
Noises. Therefore, it would be still beneficial 
To have the combined fitting approach.

Actually, I was thinking to combine these two
Optimizers and using them in tandem, in order to
Achieve some performance gain. But, the multi-
Resolution is a better one.

Regards,

George



-----Original Message-----
From: Stephen R. Aylward [mailto:aylward at unc.edu] 
Sent: Wednesday, March 16, 2005 6:23 PM
To: Li, George (NIH/NCI)
Cc: 'Luis Ibanez'; 'Insight-users at itk.org'
Subject: Re: [Insight-users] Criterion to stop 1+1_evolutionary optimizer?


Instead of adjusting the factors of the 1+1 optimizer for each level in 
the pyramid, I suggest adjusting the scalings of the parameters being 
optimized at each level.

Also, you might want to consider Mattes MI method with a gradient 
strategy instead of 1+1 when doing multi-scale optimization.  The 
justification is as follows:
* Mattes method provides effective gradients as it is a smooth metric. 
See the illustrations in the softwareGuide.
* The 1+1 optimizer is a pseudo-random search that helps avoid local 
extremes by not using gradient info.  A multi-scale approach is also 
used to avoid local extremes by essentially blurring the 
image/metric/gradient space.  So, most of the time you don't need to do 
both.   Specifically, consider using the Powel/Brent conjugate gradient 
optimizer with multi-scale registration using a Mattes MI metric.   See 
the imageRegTool application in the 
InsightApplications/LandmarkBasedMutualInformationRegistrationOrSomeSimilarL
ongName
directory (I really hate that directory name...)

Stephen

Li, George (NIH/NCI) wrote:
> Hi, Luis and all itk users:
> 
> I have found the multi-resolution samples. So, I am
> Now upgrading my registration program for a better and
> More attractive performance.
> 
> For OnePlusOneOptimizer, The growth factor seems to be
> A suitable variable to control the fitting speed for 
> Each pyramid. However, how to set a stopping criterion 
> Seems unclear to me.
> 
> Anyone has experience or idea on this matter?
> 
> Thanks,
> 
> George
> 
> 
> 
> -----Original Message-----
> From: Li, George (NIH/NCI)
> Sent: Tuesday, March 15, 2005 12:28 PM
> To: Li, George (NIH/NCI); 'Luis Ibanez'
> Cc: Insight-users at itk.org
> Subject: Registration performance
> 
> 
> Hi, Luis:
> 
> Sometime ago, you commented on improving performance
> As the following. I now understand what you meant by Multi-resolution. 
> However, is there any sample code For its implementation?
> 
> 
>>Trivial answer to your question about performance:
>>
>>            The way to improve performance
>>             is to use multi-resolution.
>>
>>You can register volumes of size 200x200x200 pixels
>>in about 20 seconds when using 3 levels of a multi- resolution 
>>pyramid, by subsampling by 2 at each level, in a typical Pentium 4 
>>machine at 2Ghz, and 512Mb of memory.
> 
> 
> Now, it seems that the registration performance has
> Become a big issue to me, and some 20 seconds for a
> Registration is much attractive, comparing with a few 
> minutes.
> 
> So, could you further provide some guidance on it?
> 
> Thanks,
> 
> George
> _______________________________________________
> Insight-users mailing list
> Insight-users at itk.org 
> http://www.itk.org/mailman/listinfo/insight-users

-- 
===========================================================
Dr. Stephen R. Aylward
Associate Professor of Radiology
Adjunct Associate Professor of Computer Science and Surgery
http://caddlab.rad.unc.edu aylward at unc.edu
(919) 966-9695

--- message truncated ---