How was this image made?

Thin section of dunite in crossed polarsFirst off, what is this?  This is a photomicrograph of dunite, an ultramafic rock composed almost entirely of the mineral olivine.  The vivid colors were produced by viewing the subject, a thin section of the rock containing birefringent crystals, through crossed polarizing filters.

This image is also a photo mosaic composed of twenty-five separate photographs.  To do this, mineralogist Julian Gray captured each photo ensuring that adjacent photos would overlap.  He used a petrographic microscope, a microscope equipped with polarizing filters and a rotating stage.  The stage was locked to ensure that no rotation occurred during the lengthy process of composing and taking twenty-five separate images.  To ensure that the rows and columns would stay aligned Julian also used a mechanical stage, a device that facilitates precise vertical and horizontal movements in tiny intervals.  Starting in one corner (in this case the upper left), the first image was snapped. Then he moved the stage to the right and slightly overlapping the first, and the next photo was taken.  In this case Julian chose a five-by-five matrix, so moving left to right, the five images in the top row were captured.  Then the stage was moved up to start the next row, being careful to verify that the rows overlapped, and the next row of images were photographed from right to left and so on until five rows of five photos were recorded.  Julian calls this process “mowing the lawn”.

Below is a series of figures illustrating the process.  The first figure shows one of the twenty-five images.  Keep track of the large pink olivine grain shaped like the African continent as we build the complete set of photos.  The next figure is a set of photos including that photo plus the eight surrounding images; nine total.  Notice the overlapping parts of the image; these are required to ensure there are no gaps in coverage when stitching them together during post-processing.  The last set of photos shows the complete set of twenty-five images used to compose the final subject.

Dunite in crossed polarized light A photo mosaic of 9 photos of a a thin section of dunite Photo mosaic of 25 photomicrographs of a dunite thin section

Up to this point the process is pretty much mechanical – standard photomicrography techniques while carefully keeping track of where you are in the series of photos.  To create the photomosaic, Julian used a feature of the stacking software he uses: Helicon Focus.  Within Helicon Focus there is a panorama function.  He opened the program, selected the panaorama function, and added the images.  Here comes the tedious part of the process.  Each image was meticulously placed to eliminate overlapping areas of adjacent photos.  Once happy with the project, Julian hit render and save.  Other photo post-processing software like Adobe Photoshop can be used, but the panorama feature of Helicon is pretty straightforward to use.

This project was an experiment that turned out pretty well.  Micro-panoramas expand the resolution of far beyond that of a single image.

Let's talk rocks.

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