# Painting on oblique images

**URL:** <https://discourse.slicer.org/t/painting-on-oblique-images/44968>\
**Category:** Support\
**Created:** [November 5, 2025, 3:03pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968 "2025-11-05T15:03:54Z")\
**Posts on this page:** 7\
**Page:** 1

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**Author:** ![Deep\_Learning](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/deep_learning/32/15345_2.png) [@Deep\_Learning](https://discourse.slicer.org/u/Deep_Learning)\
**Post date:** [November 5, 2025, 3:03pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/1 "2025-11-05T15:03:54Z")

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v5.8.1

sample data cta abdomen.

Create double oblique…

I have never understood this.

When I click with the paint tool, I do not get a circle.

I might understand this.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/9/e/9e6f6524cc192c0564ceeaceb1687ece8f9c6fa9.jpeg)

But I definitely do not understand why when i drag the circle around, it fills in?

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/2/8/28bf0762b7eb3b46c172bef0503e5607084c4d30.jpeg)

Same behavior with and without masking.

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<div class="post-metadata">

**Author:** ![pieper](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/pieper/32/8_2.png) [@pieper](https://discourse.slicer.org/u/pieper)\
**Post date:** [November 5, 2025, 4:05pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/2 "2025-11-05T16:05:15Z")

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> **[Overview](https://lassoan.github.io/SlicerSegmentationRecipes/ObliqueSliceSegmentation/)**
>
> Recipes for common medical image segmentation tasks using 3D Slicer

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<div class="post-metadata">

**Author:** ![Deep\_Learning](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/deep_learning/32/15345_2.png) [@Deep\_Learning](https://discourse.slicer.org/u/Deep_Learning)\
**Post date:** [November 5, 2025, 8:25pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/3 "2025-11-05T20:25:41Z")

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Thanks for the reply.

I was aware of this. I’m not sure that it is the exact same issue. It may be. This has always confused me.

I do not understand why when one clicks, there is one segmentation, but when one drags additional pixels are segmented.

I’ve been struggling with this issue for some time. My work around was to drag the roi until it is complete. So I am really iteratively painting away the “artifacts” without reslicing.

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<div class="post-metadata">

**Author:** ![cpinter](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/cpinter/32/7995_2.png) [@cpinter](https://discourse.slicer.org/u/cpinter)\
**Post date:** [November 6, 2025, 9:54am UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/4 "2025-11-06T09:54:00Z")

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When you paint an oblique slice it’s like painting this surface with a roller

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/b/5/b51e9bef12e62169c8dc2180e2a44a4da2f0fa1b.jpeg)

because the volume is sliced using an oblique plane.

Maybe we could add a thickness option to the paintbrush, but the solutions suggested by @lassoan (in the page referenced by @pieper) seem to be more correct.

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<div class="post-metadata">

**Author:** ![chir.set](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/chir.set/32/66982_2.png) [@chir.set](https://discourse.slicer.org/u/chir.set)\
**Post date:** [November 6, 2025, 11:16am UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/5 "2025-11-06T11:16:47Z")

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> [@cpinter](#):
>
> add a thickness option to the paintbrush

May be the `Scissors` effect could be used for painting in _most_ cases; it already has a free-form and thickness options.

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<div class="post-metadata">

**Author:** ![Deep\_Learning](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/deep_learning/32/15345_2.png) [@Deep\_Learning](https://discourse.slicer.org/u/Deep_Learning)\
**Post date:** [November 6, 2025, 12:38pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/6 "2025-11-06T12:38:50Z")

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> [@cpinter](#):
>
> When you paint an oblique slice it’s like painting this surface with a roller

That’s exactly it….. I guess the the irreproducibility that I was experiencing was a slight movement of the mouse.

Resampling is an option, but yesterday I was annotating at a bunch of angles.

\*\*\* One question, if i resample the volume then annotated on a specific slice, when I rotate back, won’t it have the same result?

I‘ve done a lot of rolling in the past. I was annotating oblique valve planes to be subtracted from another segment and need it to be complete 3d disk. Rolling, fill holes, etc.

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<div class="post-metadata">

**Author:** ![cpinter](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/cpinter/32/7995_2.png) [@cpinter](https://discourse.slicer.org/u/cpinter)\
**Post date:** [November 6, 2025, 2:10pm UTC](https://discourse.slicer.org/t/painting-on-oblique-images/44968/7 "2025-11-06T14:10:43Z")

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I think this is an important aspect, that you want to segment on multiple different oblique directions. In this case I don’t suggest resampling, because every time you do that, you lose some image quality (and segmentation fidelity).

In this case I suggest oversampling the segmentation. I just tried it and it seems to work well for oblique painting:

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/6/3/632afadc43b09d7f79b9b220adf55c93006df546.png)