11.4. ITK Approximate Signed Distance Map Image Filter

Computes a fast, approximate signed distance map from the object boundaries in a binary image.

Group (Subgroup)

ITKDistanceMap (DistanceMap)

Description

A distance map replaces every pixel with its distance to the nearest object boundary. This filter produces a signed distance map: pixels inside an object are given negative distances, and pixels outside an object are given positive distances. The magnitude of each value is the (approximate) distance, in pixels, from that pixel to the closest object boundary.

The distances are Chamfer distances, a fast approximation to true Euclidean distance. This filter trades some accuracy for speed. If you need a closer approximation to Euclidean distance, use the Danielsson or Signed Maurer distance maps instead.

Use a signed distance map when you need a smooth field that grows away from object boundaries in both directions — for example, as a speed/level-set input, for shape morphing, or to find points a fixed distance from a feature edge.

Note: distances are computed and stored as floating-point values. Choose a floating-point output array type; an integer output cannot represent fractional or negative distances correctly.

Parameter Guidance

The binary input is interpreted using two intensity values:

• Inside Value — the pixel intensity that marks the object (foreground). Default 1.

• Outside Value — the pixel intensity that marks the background. Default 0.

For example, in a typical mask where objects are labeled 1 and background is 0, set Inside Value = 1 and Outside Value = 0. If your mask labels objects as 255 on a 0 background, set Inside Value = 255 and Outside Value = 0.

The filter runs slightly faster when Inside Value is less than Outside Value; otherwise an extra pass over the image is required.

Required Input Sources

Requires a binary (two-value) image where one intensity marks objects and the other marks background. This is typically a segmentation mask produced by a thresholding or segmentation filter upstream.

See Also

• ITK Danielsson Distance Map Image Filter

• ITK Signed Danielsson Distance Map Image Filter

• ITK Signed Maurer Distance Map Image Filter

• ITK ApproximateSignedDistanceMapImageFilter (ITK Doxygen)

Input Parameter(s)

Parameter Name	Parameter Type	Parameter Notes	Description
Inside Value	Scalar Value	Float64	Set/Get intensity value representing the interior of objects in the mask.
Outside Value	Scalar Value	Float64	Set/Get intensity value representing non-objects in the mask.

Input Cell Data

Parameter Name	Parameter Type	Parameter Notes	Description
Image Geometry	Geometry Selection	Image	Select the Image Geometry Group from the DataStructure.
Input Cell Data	Array Selection	Allowed Types: int8, uint8, int16, uint16, int32, uint32, int64, uint64	The image data that will be processed by this filter.

Output Cell Data

Parameter Name	Parameter Type	Parameter Notes	Description
Output Image Data Array	DataObjectName		The result of the processing will be stored in this Data Array.

Example Pipelines

License & Copyright

Please see the description file distributed with this Plugin

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