Preliminary Result on Optimum Seed Generation Bandwidth for Object-Based Image Segmentation (OBIS) of Porphyritic Igneous Thin Sections




Crystal size distribution (CSD) analysis is one of many methods for studying the crystallization history of magma. It involves labor-intensive digitation of all crystals, which may prolong the processing of large data sets. This study presents a preliminary result of Object-Based Image Segmentation (OBIS) as a semi-automatic approach in crystal digitation. Five data sets containing 9 photomicrographs of porphyritic igneous rock thin sections were processed using SAGA GIS. The procedure produced an optimum bandwidth equation of y = 38.455 ln(x) + 114, where x is the average size of sampled crystal in mm. Segmentation tests on another sample using the formula returned good and consistent results with important notes on sensitivity to textures which may result in crystal segment separation, such as fractures, veins, and sieve, as well as the inability to separate all groundmass crystals. Even though it shows good results, this formula only applies where the pixel-to-length conversion factor of 562.2 pixel/mm.

Keywords: OBIS, SAGA GIS, Optimum bandwidth, Photomicrograph, Porphyritic igneous rock thin section.


Download data is not yet available.


Asmussen, P., Conrad, O., Günther, A., Kirsch, M., Riller, U., 2015. Semi-automatic segmentation of petrographic thin section images using a “seeded-region growing algorithm†with an application to characterize wheathered subarkose sandstone. Computers & Geosciences 83, 89–99.

Cashman, K.V., Ferry, J.M., 1988. Crystal size distribution (CSD) in rocks and the kinetics and dynamics of crystallization: III. Metamorphic crystallization. Contributions to Mineralogy and Petrology 99, 401–415.

Conrad, O., Bechtel, B., Bock, M., Dietrich, H., Fischer, E., Gerlitz, L., Wehberg, J., Wichmann, V., Böhner, J., 2015. System for automated geoscientific analyses (SAGA) v. 2.1. 4. Geoscientific Model Development 8, 1991–2007.

Higgins, M.D., 1996. Magma dynamics beneath Kameni volcano, Thera, Greece, as revealed by crystal size and shape measurements. Journal of Volcanology and Geothermal Research 70, 37–48.

Kölln, S., Conrad, O., Riller, U., n.d. Quantification of the fractal dimension of cataclasites in granitoid target rocks of the Chicxulub impact crater (Yucatán peninsula, Mexico) using SAGA GIS image analysis.

Nugroho, R.P., Disando, T., Kurniawan, I.A., Abdurrachman, M., 2019. Crystal size distribution (CSD) of plagioclase phenocryst-microphenocryst and the calculation of crystal resident times in the continuous central eruption sequences of Mount Lasem, Central Java, Indonesia. J. Phys.: Conf. Ser. 1363, 012041.

Schneider, C.A., Rasband, W.S., Eliceiri, K.W., 2012. NIH Image to ImageJ: 25 years of image analysis. Nature Methods 9, 671–675.