# local threshold: bugs or features?

**URL:** <https://discourse.slicer.org/t/local-threshold-bugs-or-features/40671>\
**Category:** Support\
**Created:** [December 13, 2024, 5:06am UTC](https://discourse.slicer.org/t/local-threshold-bugs-or-features/40671 "2024-12-13T05:06:33Z")\
**Posts on this page:** 1\
**Showing post:** 2

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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:** [December 13, 2024, 5:17am UTC](https://discourse.slicer.org/t/local-threshold-bugs-or-features/40671/2 "2024-12-13T05:17:37Z")

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> [@sulli419](#):
>
> what is Ctrl+ click is doing

Creates a seed for segmentation and then uses that seed for region growing.  
The seed is generated by thresholding with the chosen intensity range, then keeping the island where you Ctrl-clicked.

> [@sulli419](#):
>
> why can’t I paint a precise discontinuous set of pixels to set my local threshold maybe even between slices

You can certainly do this, by simply using the `Paint` effect and then using `Grow from seeds` effect. `Local threshold` just automates painting of the seed (replaced 5-10 clicks by one click).

> [@sulli419](#):
>
> but when I got to third, it never commits the flashing pixels to a segment

When the island at the clicked position is determined, the thresholding result is eroded to prevent small, thin connections between islands leading to adding unrelated regions to the seed. If the region you clicked on was relatively small then this erosion removes it completely and nothing can be drawn there. You can reduce the `Minimum diameter` parameter to avoid this.

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_[View the full topic](https://discourse.slicer.org/t/local-threshold-bugs-or-features/40671)._