For more than two materials, Multi-Phase Segmentation often yields better results than the Multiple Thresholds method. If there are bright artifacts at the borders of different materials or if the contrast is low, Multi-Phase Segmentation can be used to fill in these uncertain regions based on the watershed algorithm. This makes it very useful for avoiding partial volume effects.

Enter the name of the file or folder containing the results in the Result File Name (*.gdr) box. Choose a name that fits the current project.

Select the Number of Phases in your dataset. This can be any value between 2 and 255. Choose the Materials for each phase from the Material Database.

Define the gray value Ranges assigned to each phase by adjusting the sliders. The upper limit of each range must be smaller than the lower limit of the next range. If they are equal, the gray value is assigned to the next phase. For example, if Range 1 is defined as 20-50 and Range 2 is defined as 50-70, then the gray value of 50 is assigned to Material 2.

The watershed algorithm is used to fill all remaining uncertain areas, i.e., gray values not contained within a defined range.

Click Create Segmentation to apply the multi-phase segmentation to the image dataset. You can find a description of the results here.

In the following example, the gray values are divided into three phases. Material 1 is assigned as pore space with a gray value range of 0 to 80. Material 2 is defined as solid, with a range set to 90–100. The second solid material is defined in Material 3, with its range set to 130–255. Thus, the gray values 81–89 and 101–129 are not assigned to any phase. This can be observed in the 2D Slice Visualization section when Visibility is turned on. Gray values in Range 1 are marked in white, those in Range 2 in red, and those in Range 3 in green. All other gray values are unmarked. After creating the segmentation, the watershed algorithm fills these.