# How to use local threshold

**URL:** <https://discourse.slicer.org/t/how-to-use-local-threshold/40909>\
**Category:** Feature requests\
**Tags:** threshold\
**Created:** [December 30, 2024, 5:53pm UTC](https://discourse.slicer.org/t/how-to-use-local-threshold/40909 "2024-12-30T17:53:49Z")\
**Posts on this page:** 1\
**Showing post:** 4

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**Author:** ![jamesobutler](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/jamesobutler/32/7511_2.png) [@jamesobutler](https://discourse.slicer.org/u/jamesobutler)\
**Post date:** [January 3, 2025, 10:49pm UTC](https://discourse.slicer.org/t/how-to-use-local-threshold/40909/4 "2025-01-03T22:49:23Z")

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Generally it is the minimum diameter of the GrowCut algorithm that has to be adjusted for local threshold as the effect is more so a combo effect that is “Threshold+Grow From Seeds”.

> [@local threshold: bugs or features?](https://discourse.slicer.org/t/local-threshold-bugs-or-features/40671/2):
>
> 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. 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). When the island at the clicked position is determined, the thresholding result is eroded to prevent small, thin…

@Thomas_K, @lassoan, @pieper and myself diiscussed this same topic about the confusion of the effect at the following hangout (linked below) with Thomas proposing a “Fast local threshold” which always picks the selected voxels such as a “Threshold+Islands” type of combo effect rather than being only based on the Grow From Seeds approach. That way what you click is what you get. From that discussion it seemed that @lassoan recognized the confusion in the current effect, but there was no clear consensus about the integration of such a “Threshold+Islands” type approach.

> [@2024.10.19 Weekly Meeting - 11 AM start!](https://discourse.slicer.org/t/2024-10-19-weekly-meeting-11-am-start/40250/2):
>
> Agenda item topic: Modification / addition to Local Thresholding segment effect ([SlicerSegmentEditorExtraEffects/SegmentEditorLocalThreshold at master · lassoan/SlicerSegmentEditorExtraEffects · GitHub](https://github.com/lassoan/SlicerSegmentEditorExtraEffects/tree/master/SegmentEditorLocalThreshold))

The regular “Threshold” effect supports local histogram selection (drawn below), but then you have to use another effect to ultimately pick which selected voxels to keep from the full selection.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/9/a/9af6d22d8e2c5d2993e55a7d58e9d50eb61ceb03.jpeg)

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