[Insight-users] Re: Reg Registration

[Luis Ibanez]

Hi Prasad,

Please read carefully the description of the
MattesMutualInformation on the software guide
http://www.itk.org/ItkSoftwareGuide.pdf
Section 7.4.2, pdf-page 185.

This metric is optimal when its value is maximized.

If you look at the metric plots in figure 7.11
you will notice how noisy these family of metrics
tend to be.

----

If you switch Maximize On/Off it is totally normal
for the translations to change signs....

In one case you are asking the optimizer to go up the
hill, while in the other case you ask it to go down
the hill.... and these two directions are diametrically
oposed.

Please plot the metric values of your experiments.
Using anything from Excel to GNUplot will help you
to get a better insight in what the registration
process is doing.


Regards,


   Luis



--------------------
Prasad Sarma wrote:
> HI Luis,
>  I did multi modality registration using Mattes Mutual
> Information and  Regular Step Gradient descent
> Optimizer and the step values to be 0.01 and 0.2 as
> usual like realignment and I got the following o/p
> 
> ------------------------------
> coregister_new.exe my3Dimage_1.mha 
> myHiResolutionImage.mha diff.mha
> 0   -0.0801886   [0.291198, 0.405267, -0.0310136]
> 1   -0.10158   [0.529372, 0.828171, -0.151121]
> 2   -0.104125   [0.884429, 1.1721, -0.226268]
> .............
> 9   -0.107101   [1.68595, 1.85622, -0.406933]
> 10   -0.110094   [1.70871, 1.87651, -0.413808]
> 11   -0.110182   [1.73333, 1.89423, -0.421273]
> 12   -0.11   [1.73715, 1.87913, -0.422402]
> Result =
>  Translation X = 1.73715
>  Translation Y = 1.87913
>  Translation Z = -0.422402
>  Iterations    = 14
>  Metric value  = -0.110261
> ----------------------------------
> 
> I will study this a bit more in detail. I did not set 
> MAximizeOn() or MinimizeOn() for this program because
> I did not clearly understand which should be set when.
> I could not find clearly from manual.I am just making
> a decision based on the no of iterations , whether the
> registration terminated before max iterations or after
> all. The above values are for optimizer  with
> MimimizeOn option( seems like Default), If I use
> MaximizeOn()
> I am getting
> ---------------
> coregister_new.exe my3Dimage_1.mha 
> myHiResolutionImage.mha diff.mha
> 0   -0.0801886   [-0.291198, -0.405267, 0.0310136]
> 1   -0.0812775   [-0.676488, -0.723441, 0.0131975]
> ......
> 12   -0.0785794   [-2.95363, -0.999835, -1.02956]
> 13   -0.0760981   [-2.95954, -1.03052, -1.02999]
> 14   -0.0721892   [-2.95988, -1.0149, -1.03005]
> 15   -0.0709626   [-2.96124, -0.999333, -1.03018]
> Result =
>  Translation X = -2.96124
>  Translation Y = -0.999333
>  Translation Z = -1.03018
>  Iterations    = 17
>  Metric value  = -0.0760867
> ------------------------------
> Why are the translations shown in opposire directions
> for the optiomizer Maximize Minimize values?
> May be this will answer my problem.
> Thanks alot and sorry for big mails.
> Prasad
> 
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