[Insight-users] NormalizedCorrelationImageToImageMetric speedup

[Andinet Enquobahrie]

Hi Marius,

Can you please write a short description of your improvements to the 
NormalizedCorrelationImageToImageMetric class and submit your 
description with the code to the InsightJournal.

http://insightsoftwareconsortium.org/InsightJournal/

thank you

-Andinet

> Hi all,
>
> The current GetDerivative() and GetValueAndDerivative() from the 
> NormalizedCorrelationImageToImageMetric loop twice over the fixed 
> image. This is not neccesary, one time is enough to calculate the 
> metric value and the derivative to the transform parameters. I have 
> rewritten this class to do so, and this gives the expected (almost) 
> two times speedup.
>
> Also I have added the possibility to compute the metric over only a 
> random subset of the fixed image pixels. This reduces the computation 
> time (substantially), while convergence properties are maintained. It 
> is similar to the MattesMutualInformationMetric, but there a fixed 
> subset is used.
>
> I have added this code as an attachment. Feel free to commit it to the 
> repository (the code also contains some small bug fixes). I have 
> tested that, when using all pixels in the fixed image, the new code 
> gives exactly the same output as the current itk code.
>
> I have also implemented the possibillity to use a random subset in the 
> MeanSquaresImageToImageMetric (shouldn't that be called the 
> MeanSquareDifferenceImageToImageMetric?) This is also attached.
>
> Regards,
>
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