# Question from enabling opacity mapping in categorical colors
**URL:** https://discourse.paraview.org/t/question-from-enabling-opacity-mapping-in-categorical-colors/12890
**Category:** ParaView Support
**Created:** [September 20, 2023, 3:23am UTC](https://discourse.paraview.org/t/question-from-enabling-opacity-mapping-in-categorical-colors/12890 "2023-09-20T03:23:10Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@fashing](https://discourse.paraview.org/u/fashing)
#### Post date: [September 20, 2023, 3:23am UTC](https://discourse.paraview.org/t/question-from-enabling-opacity-mapping-in-categorical-colors/12890/1 "2023-09-20T03:23:10Z")
Hi Paraview,
This is a simple question related to my previous [post](https://discourse.paraview.org/t/some-questions-about-categorical-colors/12860).
While I applied opacity mapping on this cube, I saw through it.
 
I understand this means there is no “surface” in the contacting area between sub-cube, which is reasonable. I am just curios if we can set something to make the surface exist (maybe set something for verbose surface?) or is there a way to remove sub-cube like I intended to.
I know `threshold` filter works, but it is heavy and not flexible. I also tried different options in `Backface Representation`, but none of them works.
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### Author:  [@mwestphal](https://discourse.paraview.org/u/mwestphal)
#### Post date: [September 20, 2023, 11:51am UTC](https://discourse.paraview.org/t/question-from-enabling-opacity-mapping-in-categorical-colors/12890/2 "2023-09-20T11:51:49Z")
Not as-is with surface representation. What you are looking for is “Masked Cells” which is supported by most type of vtkDataSet. But you must set it on the data.