# Viewing a volume with two different volume rendering properties at same time

**URL:** <https://discourse.slicer.org/t/viewing-a-volume-with-two-different-volume-rendering-properties-at-same-time/16411>\
**Category:** Support\
**Tags:** volume-rendering\
**Created:** [March 7, 2021, 12:49pm UTC](https://discourse.slicer.org/t/viewing-a-volume-with-two-different-volume-rendering-properties-at-same-time/16411 "2021-03-07T12:49:21Z")\
**Posts on this page:** 1\
**Showing post:** 10

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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:** [March 8, 2021, 4:31pm UTC](https://discourse.slicer.org/t/viewing-a-volume-with-two-different-volume-rendering-properties-at-same-time/16411/10 "2021-03-08T16:31:53Z")

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> [@mohammed\_alshakhas](#):
>
> is that a preset available in slicer the one you used here for the cbct rendering ?

It is not a built-in preset, but you can choose a similar built-in preset, modify it by drag-and-dropping control points in the transfer functions, and then add it to the preset list. See:

- [I want to boot up with my very own color map and a black background](https://discourse.slicer.org/t/i-want-to-boot-up-with-my-very-own-color-map-and-a-black-background/16383/)
- [Create volume rendering presets](https://discourse.slicer.org/t/create-volume-rendering-presets/16339)

> [@mohammed\_alshakhas](#):
>
> what’s difference between gradient opacity and scalar map opacity ?

Scalar opacity mapping allows you to assign opacity to a voxel based on its intensity value. It can be used to suppress visibility (set opacity to 0) of soft tissues, without impacting visibility of bone.

Gradient opacity mapping allows you to assign opacity to a voxel based on the rate of intensity change at that position. This can be used to enhance regions where there is a sudden intensity change, such as skin surface (air/soft tissue intensity are very different) and bone surface (bone/soft tissue intensity are very different).

Probably you can achieve the best results by tuning all transfer functions.

Once you figure out what general shape of transfer function works, you would usually create a simple module that allows the user to generate that transform function using 3-4 sliders:

- size and position of gap between the two scalar opacity mapping function peaks
- height of the “skin” peak
- threshold in gradient opacity mapping function below that the opacity is set to 0

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