Applying Morphological Operations

The morphological operations of dilation, erosion, opening, closing, and smooth can be applied to refine regions of interest and the selected classes of a multi-ROI by growing, shrinking, or smoothing labeled regions. The precise effect of these operations is determined by the selected structuring element. If the Use range option is selected, then the operation will be limited to the available range (see Defining Intensity Ranges).

Morphological operations box

Morphological operations
  Description
Dilate Expands a region of interest using the selected structuring element (see Structuring Element).
Erode Shrinks a region of interest using the selected structuring element (see Structuring Element).
Open Is an erosion followed by a dilation using the same structuring element for both operations. In general, opening is less destructive than erosion. The effect of the operator is to preserve foreground regions that have a similar shape to the structuring element, or that can completely contain the structuring element, while eliminating other foreground pixels (see Structuring Element).
Close Is a dilation followed by an erosion using the same structuring element for both operations. The effect of the operator is to preserve background regions that have a similar shape to the structuring element, or that can completely contain the structuring element, while eliminating other background pixels (see Structuring Element).
Smooth Smooths a region of interest using the selected structuring element (see Structuring Element).

Smoothing can be required in some cases to remove noise from the surface of an object. An example of smoothing is show in the following screen captures.

Original ROI (left) and smoothed ROI (right)

The following settings are available for morphological operations.

Settings for morphological operations
  Description
Dimensionality Lets you apply the selected morphological operation in 3D, in which case the operation will be applied to all axes, or in 2D, in which the case the operation can be applied along the X, Y, or Z axis.
Shape Lets you choose the shape and size of the neighborhood that will be sampled when calculating the pixel values to be modified (see Structuring Element).
Range Lets you choose selected slices, a range of image slices and an increment, or a combination of both, to which the selected morphological operation will be applied. For example, if you enter 1,2,3-5,6-15/3, then the operation will be applied to slices 1, 2, 3, 4, 5, 6, 9, 12, and 15.
Kernel size Lets you choose the size of the neighborhood that will be sampled when calculating the pixel values to be modified (see Structuring Element).
How to Apply a Morphological Operation
  1. Select the required region of interest or multi-ROI class(es) in the Data Properties and Settings panel.
  2. Select the Use range option in the Range box if you want to limit the selected operation to a defined data range (see Defining Intensity Ranges).
  3. Select the required dimensionality for the selected operator — 3D, 2D (X), 2D (Y), or 2D (Z).

    Note Per slice 2D interpretation is generally faster than 3D processing and may give similar results. When setting interpretation to 3D, the filter is applied to the 3D slab with a depth depending on encoded parameters.

  4. Select a shape and size for the structuring element that will be used for the selected operator.

    Note Structuring elements are retained in memory. The last used settings will appear by default.

  5. Choose a range within which the selected operator will be applied, optional.
  6. Click the button — Dilate, Erode, Open, Close, or Smooth — that represents the operation you want to apply.