Texture analysis
Four samples cut along planes striking NS and dipping 45ยบ E
(approximately paleovertical) were analyzed in thin section using a
petrographic microscope at the Nature Lab at the Rhode Island School of
Art and Design. The microscope renders mosaics of each sample consisting
of stitched together portions of an individual sample. The orientation
of the planes along which thin sections were made was chosen to
investigate whether magmatic folation due to gravity was detectable in
samples. Grain boundaries were identified using image processing,
following the technique implemented by Barraud (2006). This technique
makes use of the watershed segmentation function of the Insight Toolkit
(ITK). ITK is an open-source and cross-platform library that is
implemented in C++. The watershed segmentation technique is applied to
the images using the function WatershedSegmentation1.cxx included
with the ITK examples build. The function uses an anisotropic diffusion
filter to smooth the image and then converts the image to greyscale. A
gradient function is then applied to the image which is then saturated
to allow for the segmentation of individual grains. The grain boundary
images are then thresholded and analyzed in ImageJ, approximating
individual grains as ellipses, to obtain information about the
orientation of each grain/ellipse.