The Phansalkar filter is a modification based on the publication by Sauvola and Pietikäinen (2000) and deals with low contrast images. For detailed information about the theory also refer to Phansalkar et al. (2011).

The Sphere Radius controls the size of the region, in which the filter is applied.

The local threshold T is found from the mean (m) and standard deviation (s) of the pixel intensities as follows:

R is the dynamic range of standard deviation, which is equal to 0.5 for a normalized image, and K is a constant which takes values in the range [0.2, 0.5]. p and q are constants.

The local mean and standard deviation adapt the value of the local threshold.

Click Create Segmentation to segment the gray value image with the Phansalkar method. This thresholding method does not create a GeoDict result file. The resulting structure is displayed in the GeoDict visualization area. The gray value image stays in memory and can be compared to the structure. Check Structure and uncheck Volume Field in the visualization panel above of the visualization area to only visualize the structure.

To save the structure in a *.gdt file select File → Save Structure as from the menu bar in the main GeoDict GUI.