9.64. ITK Relabel Component Image Filter

Relabel the components in an image such that consecutive labels are used.

Group (Subgroup)

ITKConnectedComponents (ConnectedComponents)

Description

RelabelComponentImageFilter remaps the labels associated with the objects in an image (as from the output of ConnectedComponentImageFilter ) such that the label numbers are consecutive with no gaps between the label numbers used. By default, the relabeling will also sort the labels based on the size of the object: the largest object will have label #1, the second largest will have label #2, etc. If two labels have the same size their initial order is kept. The sorting by size can be disabled using SetSortByObjectSize.

Label #0 is assumed to be the background and is left unaltered by the relabeling.

RelabelComponentImageFilter is typically used on the output of the ConnectedComponentImageFilter for those applications that want to extract the largest object or the “k” largest objects. Any particular object can be extracted from the relabeled output using a BinaryThresholdImageFilter . A group of objects can be extracted from the relabeled output using a ThresholdImageFilter .

Once all the objects are relabeled, the application can query the number of objects and the size of each object. Object sizes are returned in a vector. The size of the background is not calculated. So the size of object #1 is GetSizeOfObjectsInPixels() [0], the size of object #2 is GetSizeOfObjectsInPixels() [1], etc.

If user sets a minimum object size, all objects with fewer pixels than the minimum will be discarded, so that the number of objects reported will be only those remaining. The GetOriginalNumberOfObjects method can be called to find out how many objects were present before the small ones were discarded.

RelabelComponentImageFilter can be run as an “in place” filter, where it will overwrite its output. The default is run out of place (or generate a separate output). “In place” operation can be controlled via methods in the superclass, InPlaceImageFilter::InPlaceOn() and InPlaceImageFilter::InPlaceOff().* ConnectedComponentImageFilter , BinaryThresholdImageFilter , ThresholdImageFilter

Input Parameter(s)

Parameter Name

Parameter Type

Parameter Notes

Description

Minimum Object Size

Scalar Value

UInt64

Set the minimum size in pixels for an object. All objects smaller than this size will be discarded and will not appear in the output label map. NumberOfObjects will count only the objects whose pixel counts are greater than or equal to the minimum size. Call GetOriginalNumberOfObjects to find out how many objects were present in the original label map.

SortByObjectSize

Bool

Controls whether the object labels are sorted by size. If false, initial order of labels is kept.

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 Cell Data

DataObjectName

The result of the processing will be stored in this Data Array inside the same group as the input data.

Example Pipelines

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