# Rendering Performance with Large number of slab slices

**URL:** <https://discourse.slicer.org/t/rendering-performance-with-large-number-of-slab-slices/8351>\
**Category:** Development\
**Created:** [September 9, 2019, 10:01pm UTC](https://discourse.slicer.org/t/rendering-performance-with-large-number-of-slab-slices/8351 "2019-09-09T22:01:29Z")\
**Posts on this page:** 1\
**Showing post:** 3

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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:** [September 9, 2019, 11:44pm UTC](https://discourse.slicer.org/t/rendering-performance-with-large-number-of-slab-slices/8351/3 "2019-09-09T23:44:34Z")

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Yes, this performance is expected if you use CPU for raycasting.

See instructions in this post how to configure the GPU volume renderer to create projection image: [Is it possible to change a cbct to 2d](https://discourse.slicer.org/t/is-it-possible-to-change-a-cbct-to-2d/7617)

If you want to limit the slab to a certain thickness then set the volume rendering clipping ROI’s Z size to the desired thickness and then apply the SlicerToRAS transform of the slice view to this ROI.

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_[View the full topic](https://discourse.slicer.org/t/rendering-performance-with-large-number-of-slab-slices/8351)._