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Home < Documentation < Nightly < Modules < SegmentEditor

For the stable Slicer documentation, visit the 4.10 page.

Introduction and Acknowledgements

This page is a work in progress

Module Description

Use Cases

Create segmentations that can be used for:

  • Surgical/radiation therapy planning
  • Intra-surgery navigation
  • Volume/shape analysis
  • 3D printing
  • Further processing

Panels and Their Uses


Effects operate either by clicking the Apply button in the GUI or by clicking and/or dragging in the slice view. For operations where you use the GUI, the target label map is the one in the Red slice viewer. Otherwise the target is based on which slice viewer you click in. To use, select the label value for the tools to work on. Clicking on the colored box will provide a pop-up with a selection of labels.

Paint.png Paint

Paint on the selected segment with a round brush.

  • Pick the radius (in millimeters) of the brush to apply
  • Left click to apply single circle
  • Left click and drag to draw a curve
  • A trace of circles is left which are applied when the mouse button is released
  • Sphere mode applies the radius to slices above and below the current slice.

The 'smudge' option can be used when working on the boundary between two or more regions. In this mode, the label color is set to the value of the labelmap where the first left click occurs. This mode allows you to quickly switch between colors.

Draw.png Draw

Draw segment outline in slice viewers.

  • Left click to lay individual points of an outline
  • Left drag to lay down a continuous line of points
  • 'x' key to delete the last point added
  • Right click or 'a' key to apply outline to label map


Left-click and drag in slice or 3D viewers to erase from the current segment with a round brush. The radius can be adjusted. Additional brush modes include sphere brush and pixel mode.

LevelTracing.png Level Tracing

Add uniform intensity region to selected segment. As you move the mouse, the current background voxel is used to find a closed path that follows the same intensity value back to the starting point within the current slice. Pressing the left mouse button filles the path according to the current labeling rules.

Rectangle.png Rectangle

Add a rectangular area to the selected segment

  • Left click and drag to sweep our

ErodeLabel.png Margin

Grow or shrink the selected segment by a specified margin size. A positive margin size makes the segment grow while a negative margin size makes the segment shrink.

GrowCutSegment.png GrowCut

GrowCut is a powerful algorithm that uses example segmentation to create a full segmentation of the volume. You can use multiple label colors to define regions that represent parts of anatomical structures and then let the GrowCut algorithm seek out a best labeling for adjacent pixel so they match your example.

To use this, you first define your example segmentation using the normal paint or draw tools as described above. Define at least two structure classes and then click Apply. If you are not satisfied with the result, use the Undo button to go back and modify your example.

See the Grow Cut documentation for more details.

Also see the Fast GrowCut documentation. This is an effect that can be added by downloading the extension. It requires memory but is a fast implementation of the GrowCut method

Threshold.png Threshold

  • Use Threshold to determine a threshold range and click on Use for Paint
  • Change into Paint or Draw and click on the Threshold button
  • begin painting/drawing

Only voxels where the background value is within the threshold range will be set to the new label value. The range is inclusive, so for example if the minimum is zero to ten, all pixels zero and above but less than or equal to ten will be included.


Smooths the selected segment by removing extrusions and filling small holes. There are four smoothing modes available: median, Gaussian, opening and closing. The median method reduces noise while preserving edges. The Gaussian method reduces image detail. The opening method removes extrusions and the closing method fills small holes.

Logical Operators

Apply logical operators on a segment or combine it with other segments. Operations include:

  • Copy from segment: Replace the selected segment by the modifier segment
  • Union with segment: Add modifier segment to current segment
  • Intersection with segment: only keeps those regions in the select segment that are common with the modifier segment
  • Subtract Segment: Subtract region of modifier segment from the selected segment
  • Clear: Clears the selected segment
  • Fill: Completely fills the selected segment

IdentifyIslands.png Identify Islands

Use this tool to create a unique label value for each connected region in the current label map. Connected regions are defined as groups of pixels which touch each other but are surrounded by zero valued voxels. If FullyConnected is selected, then only voxels that share a face are counted as connected; if unselected, then voxels that touch at an edge or a corner are considered connected.

Note: Be aware that all non-zero label values labels values are considered equal by this filter and that the result will renumber the resulting islands in order of size. Note: The output label values use the currently selected color table, but the names assigned to islands are arbitrary. Label values are assigned in order of the size of the island starting with 1. The value of 0 is assigned to the background.



  • f - move to next slice
  • b - move to previous slice
  • h - toggle the crosshair and put it into navigator mode

Effect Selection

  • Escape - cancel current effect
  • p - select Paint effect
  • d - select Draw effect
  • e- select Eraser effect
  • r - select Rectangle effect

Draw Effect Keystrokes

  • a or Enter - apply the current outline
  • x - delete last point added

Paint Effect Keystrokes

  • - or _ - shrink the current radius by 20%
  • + or = - grow the current radius by 20%