ConvexHull

MLModule

genre	Region
author	MeVis Medical Solutions AG
package	MeVisLab/Standard
dll	MLFuzzy
definition	MLFuzzy.def
see also	Rank
keywords	gaps, holes, close, 2D

Purpose

The module ConvexHull calculates the 2D (slice-wise) convex hull of one or more objects.

Objects are defined by voxels with the same non-zero value. For each object in the image, all voxels with at least one zero-valued neighbor are first collected and then connected. Afterward, holes inside the object are filled. Background voxels are assigned zero values.

Note that the module is designed to find multiple objects in an image. Each object must be identifiable by its unique voxel value. The input image is scanned Num Objects times (which may be slow for a large number of objects), and during each scan, the input image is checked for voxels corresponding to the value of the current object number.

Details

Depending on the object size, the calculation can take a while but is quite fast for 2D.

If the module’s Num Objects field is set to 1 (default), only voxels with a value of 1 are considered for the computation of the convex hull.

If the input image contains an object consisting of voxels with a value of, for example, 255, the Num Objects field must be set to 255 to detect the object correctly. However, this would result in 254 scans of the entire input image with no objects found, and only on the 255th scan would the object be detected. In such cases, it is recommended to leave the Num Objects field at 1 and modify the object voxel values in the input image to 1 (e.g., by using a Scale or thresholding module).

Windows

Default Panel

Input Fields

input0

name: input0, type: Image

The input image of a scalar type.

Since the objects are found by their voxel value and this value needs to correspond to the object number, the objects’ voxel values should be of an integer type.

Output Fields

output0

name: output0, type: Image

The convex hull of the objects in the input image.

The voxel values of the convex hull(s) in the output image correspond to the object number and thus to the voxel values in the input image.

Parameter Fields

Visible Fields

Num Objects

name: numObjects, type: Integer, default: 0

Sets the number of objects to scan for, and consequently, the number of scans. In each scan, the module searches for objects with voxel values corresponding to the current object number.

If the field is set to 2, the module first scans for voxels with a value of 1, forming one object, and then for voxels with a value of 2, forming another object.