# Smoothing Recursive Gaussian Image Filter

**URL:** https://discourse.slicer.org/t/smoothing-recursive-gaussian-image-filter/14292
**Category:** Support
**Created:** [October 28, 2020, 7:45pm UTC](https://discourse.slicer.org/t/smoothing-recursive-gaussian-image-filter/14292 "2020-10-28T19:45:29Z")
**Posts on this page:** 3
**Page:** 1

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### Author: ![aseman](https://avatars.discourse-cdn.com/v4/letter/a/c0e974/32.png) [@aseman](https://discourse.slicer.org/u/aseman)
#### Post date: [October 28, 2020, 7:45pm UTC](https://discourse.slicer.org/t/smoothing-recursive-gaussian-image-filter/14292/1 "2020-10-28T19:45:29Z")

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Slicer version:4.10.1  
Hi 3D Slicer experts and all  
I used Smoothing Recursive Gaussian Image Filter from simple filters module. My input volume is a CT image and I chose various sigma values, which in the below figure, the result of this selection in each row, have been shown. (σ1= 3, 0.0001, 0.0001 / σ2= 0.0001, 3, 0.0001 / σ3= 0.0001, 0.0001, 3).  
I can’t distinguish each of this σ values affect on which view (axial, sagittal or coronal). In the other words, what is the difference among σ1, σ2 and σ3 ?  
Also, along which axis or on which view ( axial, sagittal, or coronal) does σ1 have the greatest influence?  
Thanks a lot

 ![Screenshot_1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/c/ac7a47ab6fc3720f1b1edfe154e65b03cbb89200.png)

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### Author: ![aseman](https://avatars.discourse-cdn.com/v4/letter/a/c0e974/32.png) [@aseman](https://discourse.slicer.org/u/aseman)
#### Post date: [November 1, 2020, 8:27pm UTC](https://discourse.slicer.org/t/smoothing-recursive-gaussian-image-filter/14292/2 "2020-11-01T20:27:23Z")

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Hi 3D slicer experts and all  
Unfortunately, I didn’t receive any feedback. In Smoothing Recursive Gaussian Image Filter, I selected different values for Sigma. Finally, I find that for Sigma with three components (a,b,c), it seems that if a\>\> b and c , the Sagittal view is the sharpest. Also, for b\>\> a and c; Coronal view is the sharpest and for c\>\> a and b, Axial view is the sharpest (like the below figure).  
So, can we conclude that “a” component has the most smoothing on L-R axis, “b” component on A-P and “c” component on S-I? In other words, do the “a, b,and c” components have the most smoothing on RAS, respectively?  
Thanks a lot

 ![pic1](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/d/ad170b619252327c3cf069924e8c3c5add8d5472.png)

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### Author: ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)
#### Post date: [November 1, 2020, 8:34pm UTC](https://discourse.slicer.org/t/smoothing-recursive-gaussian-image-filter/14292/3 "2020-11-01T20:34:03Z")

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Yes, what you describe is correct, and it is so because Slicer uses [RAS coordinate system](https://www.slicer.org/wiki/Coordinate_systems).