A microscopic information system (MIS) for petrographic analysisSimone Tarquinin , Massimiliano FavalliIstituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Pisa, 56126, Via della Faggiola 32, 56126 Pisa, Italya r t i c l e i n f oArticle history:Received 18 May 2009Received in revised form3 September 2009Accepted 4 September 2009Keywords:Granitoid rocksGeographic Information System (GIS)Image processingPetrographya b s t r a c tThe database and visualization facilities of Geographic Information System (GIS) software are employedto support the analysis of rock texture from thin section by image processing. A MicroscopicInformation System (MIS) is hence obtained. The method is applied to transmitted light images of 137samples obtained from 8 granitoid rocks. A slide scanner and a mount for crossed polarization are usedto acquire the input images. For each thin section 5 collimated RGB images are scanned: 4 underdifferent directions of crossed polarization and 1 without polarization. A grain segmentation procedure,based on two region growing functions is applied. The output is converted to vector format and refinedusing editing tools in the MIS environment, which enables a straightforward match between the inputimagery and the final vectorized texture. GIS software provides optimal management of the MISdatabase, allowing the cumulative measurement of more than 87,000 grains.& 2010 Elsevier Ltd. All rights reserved.1. IntroductionA great variety of images types are employed in the Earth andplanetary sciences, ranging from microscopic scale images of rocksamples to continental scale satellite surveys. The instrumentsdeveloped for different scales of examination are based on varioustechnologies, but in general the common basis is a sensor thatrecords a signal from the target surface to produce an image.Different types of software have been developed to deal withsuch signals, ranging from remote sensing to image processingunits, but Geographic Information System (GIS) software isparticularly flexible, allowing the combined handling and visua-lization of data in different formats over a wide resolution range(Burrough, 1989; Pareschi et al., 2000). This software has beenrecently introduced to the study of rock textures at microscopicscale, using transmitted light microscope images. Li et al. (2008)use GIS software for the segmentation and analysis of grainboundaries, presenting a procedure tested on a few samples.Barraud (2006) applies GIS software to refine and analyze thevectorized texture obtained after segmenting transmitted lightmicroscopy images with third party software (ITK, for ImageToolkit, http://www.itk.org). Fernandez et al. (2005) use GISsoftware to compute shape-fabric parameters and strain factorsfrom grain boundary maps. In this paper, we present a systemwhich uses GIS software to manage the analysis of a largecollection of thin sections, applying a custom image processingprocedure based on region growing algorithms. This systemrepresents a stand-alone, inexpensive tool that can substitute forthe microscope itself in performing a preliminary petrographicsurvey. It also allows for statistical examination of coarse grainedrocks which is difficult with regular microscopes. Any geographicreference is absent, hence we prefer to call the obtainedInformation System ‘‘Microscopic’’ instead of geographic (MIS).Petrographic analysis of thin sections by transmitted lightmicroscopy is one of the principal methods for rock characteriza-tion and classification. Digital image analysis is the process ofidentifying and quantifying features in a digital image startingfrom pixel values (Russ, 2002). When applied to transmitted lightmicroscopy images, the aim of image analysis is to quantify therock composition and texture by measuring parameters such asmodal fractions, crystal/grain size distributions and crystal/grainshapes. These features result from petrogenetic processes, andtheir accurate determination is central in the fields of petrology,volcanology or tectonics (e.g. Jerram et al., 2003; Boorman et al.,2004; Higgins, 2006; Trullenque et al., 2006; Williams et al., 2006;Keulen et al., 2007; Fornaciai et al., 2008; Piochi et al., 2008).Several authors have applied digital image analysis to auto-mate and speed up the quantification of rock texture fromtransmitted light microscopy images of thin sections (e.g.Armienti et al., 1994; Launeau et al., 1994; Lumbreras and Serrat,1996; Goodchild and Fueten, 1998; Launeau and Cruden, 1998;Heilbronner, 2000). However, the application of this method tomany rocks is hampered by the complexity of related transmittedlight microscopy images.Here we address the problem of digital image analysis of thinsections by applying four approaches: (i) the use of a slide scannerto acquire input imagery in transmitted light from thin sections,leaving aside the petrographic microscope (De Keyser, 1999;ARTICLE IN PRESSContents lists available at ScienceDirectjournal homepage: www.elsevier.com/locate/cageoComputers & Geosciences0098-3004/$-see front matter & 2010 Elsevier Ltd. All rights reserved.doi:10.1016/j.cageo.2009.09.017n Corresponding author: Tel.: +39 050 8311932; fax: +39 050 8311942.E-mail address: tarquini@pi.ingv.it (S. Tarquini).Computers & Geosciences 36 (2010) 665–674
