Global Thresholding
Various options are available for Image Segmentation via Global Thresholding of gray values. Up to 255 thresholds can be used to define gray value ranges and assign material IDs to respective voxels. Enter the name of the file and folder that will contain the results in the Result File Name (*.gdr) field. Choose a name that fits the current project. Two Segmentation Modes are available: Single Threshold and Multiple Thresholds. The choice depends on the number of different materials in your dataset.
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Know how! You can Save your current settings for this tool as Start-Up Settings . The next time you process an image, these settings will be automatically loaded and filled into the parameter fields. You can also load the Built-In Default Settings available in GeoDict. If you change any settings and want to revert to your saved start-up settings, click the corresponding button to Load the Start-Up Settings . |
Single Threshold
In Single Threshold mode, you can use a Manual Threshold as well as one of the automatic thresholding methods: Otsu or KMeans. For more information about the theory behind these two methods, refer to the Wikipedia pages on Otsu’s method and KMeans clustering.
The value of the single Threshold separates the gray value range into two constituent materials. Material 1 (ID 00) is set to Pore by default, and Material 2 (ID 01) is set to a generic Solid. The overlay color and material selection are shown for each material. You can assign the desired material phase to each material ID by clicking the available button and following the dialog. Please refer to the Material Database User Guide for more details. You can change the overlay color through Use GeoDict Custom Colors, as explained here.
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Note! Note that the Visibility and Outline options, located in the View Options section, control the threshold visualization settings. See here for more details. You can also visualize a single threshold in 3D, as described here. |
The Volume Fraction indicates the computed volume fraction corresponding to the current Threshold value and updates automatically whenever threshold values change. For example, a Volume Fraction of 0.32 at a Threshold of 127.5 means that 32% of the image voxels have gray values above 127.5 and are assigned to Material 2.
The Density (kg/m3) of Material 2 and the selected Grammage Plane (X-Y, X-Z, or Y-Z) are used to calculate the material’s Grammage. If the density of Material 2 is known, it can be entered, and GeoDict will automatically calculate the area density for the selected plane. Only Material 2's density can be set. Material 1's density is assumed to be zero. This option is useful for materials like paper, which consist of one solid material and pore space. If you have Grammage measurements available, you can use it to choose the threshold accordingly.
Multiple Thresholds
Use Multiple Thresholds when defining more than one threshold for more than two different materials. The available Threshold Methods are: Manual Threshold, the Otsu method, and KMeans clustering.
The Otsu method is an automatic segmentation algorithm. It can be used for up to four thresholds for 8-bit images and up to two thresholds for 16-bit images. Up to 255 thresholds are available for Manual or KMeans thresholding. For more information about the underlying theory, refer to the Wikipedia pages on Otsu’s method and KMeans clustering.
The automatic thresholding methods (Otsu and KMeans) use only the histogram for segmentation. Manual thresholds are selected by moving the sliders or entering values.
Enter the Number of Thresholds to be applied. If you select multiple thresholds, they will be shown in the histogram plot at the bottom right of the dialog. For an 8-bit excerpt of a Berea sandstone, four thresholds are set. The five corresponding materials are shown in the histogram plot as determined by the Otsu method.
Click Create Segmentation to create a structure based on your image dataset and the current settings. You can find a description of the results here.
