# BSpline on multi-level registration

**URL:** https://discourse.itk.org/t/bspline-on-multi-level-registration/512
**Category:** Algorithms
**Created:** [December 14, 2017, 5:43pm UTC](https://discourse.itk.org/t/bspline-on-multi-level-registration/512 "2017-12-14T17:43:02Z")
**Posts on this page:** 4
**Page:** 1

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### Author: ![Ray](https://discourse.itk.org/letter_avatar_proxy/v4/letter/r/e9a140/32.png) [@Ray](https://discourse.itk.org/u/Ray)
#### Post date: [December 14, 2017, 5:43pm UTC](https://discourse.itk.org/t/bspline-on-multi-level-registration/512/1 "2017-12-14T17:43:02Z")

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Hello! I’m trying to understand multi-level BSpline registration in ITK.

I’m using itk::BSplineTransform as my transformation model. I set the mesh size to be 8x8x8. If I run a 2-level registration with shrinking factor of 2x1. At the second level. the mesh size will be 4x4x4, or it’s still 8x8x8?

Thanks!  
-Ray

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### Author: ![tim-evain](https://discourse.itk.org/user_avatar/discourse.itk.org/tim-evain/32/220_2.png) [@tim-evain](https://discourse.itk.org/u/tim-evain)
#### Post date: [December 17, 2017, 9:56am UTC](https://discourse.itk.org/t/bspline-on-multi-level-registration/512/2 "2017-12-17T09:56:42Z")

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Hello Ray,  
There was some improvement to the multi-level registration with the v4 framework. As far as I know, you can now define specific behavior of transform at each level thank to transform adaptators (see the [ImageRegistrationMethodv4](https://itk.org/Doxygen/html/classitk_1_1ImageRegistrationMethodv4.html) documentation). Since this is not always relevant, the default is to let the transform as it.  
So if you want to modify the mesh size for each level, you have to set it explicitely.

HTH,

Tim

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### Author: ![Ray](https://discourse.itk.org/letter_avatar_proxy/v4/letter/r/e9a140/32.png) [@Ray](https://discourse.itk.org/u/Ray)
#### Post date: [December 17, 2017, 7:58pm UTC](https://discourse.itk.org/t/bspline-on-multi-level-registration/512/3 "2017-12-17T19:58:22Z")

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Thank you Tim!

So the default is the mesh size will stay the same at different levels?

-Ray

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### Author: ![tim-evain](https://discourse.itk.org/user_avatar/discourse.itk.org/tim-evain/32/220_2.png) [@tim-evain](https://discourse.itk.org/u/tim-evain)
#### Post date: [December 18, 2017, 1:18pm UTC](https://discourse.itk.org/t/bspline-on-multi-level-registration/512/4 "2017-12-18T13:18:59Z")

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It seems yes.

Tim