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Stereoscopic Effects from Single SEM Images


Robert Sturm University of Salzburg , Department of Chemistry and Physics of Materials , Hellbrunnerstrasse 34 , A-5020 Salzburg , Austria sturm_rob@hotmail.com


Abstract: Generation of three-dimensional SEM micrographs is traditionally based on a pair of images showing the object from two different perspectives. Here a method is described by which the 3D effect can be obtained from a single photograph. This technique is founded upon the principle of object-depth mapping, where different depth levels of the object are encoded with different colors. This process enables the creation of an image stack that forms the basis for the 3D image. Several photographic examples from different scientifi c fi elds are provided in order to demonstrate the effectiveness of the method.


Keywords: scanning electron microscopy (SEM) , stereo imaging , tilted-specimen method , stereo from a single image , free software


Introduction


Three-dimensional (3D) imaging has found broad application in scanning electron microscopy (SEM) for decades [ 1 – 5 ]. While stereophotography enhances the viewer’s attraction to an object, 3D images of small objects are of scientific value in several respects: (1) surface structures of objects can be submitted to a more detailed morphometric evaluation, (2) spatial arrangement of structures can be more efficiently elucidated, and (3) measurements of objects in all three dimensions can be made under certain conditions [ 1 , 6 - 7 ]. In many cases, measurements in the third dimension are not necessary, but images exhibiting a stereo-effect can be valuable in any case.


The ability to produce a large depth of field along the optic axis, typically 100 times larger than possible by light microscopy, has been a major attribute of the SEM since its inception. Using this depth of field in the SEM, a sub-millimeter object can be imaged in stereo by taking a pair of images, where the specimen was tilted by about 7 degrees between them. Figure 1 shows this procedure and a resulting image pair coded as a red-cyan anaglyph [ 6 – 8 ]. When viewed with red-cyan glasses, stunning stereo effects can be achieved by this conventional stereo imaging method.


Recently, computer algorithms have been developed that allow the generation of stereo-images on the basis of a single SEM micrograph [ 9 ]. This method, founded on the principle of object-depth mapping, has opened new possibilities because even previously recorded electron micrographs can be subjected to a re-evaluation by viewing them in stereo. T is article describes 3D imaging based on a single SEM photograph. Besides an explanation of the steps behind this computer-aided technique, the article introduces the reader to a freely available soſt ware implementation of the method (Picolay) [ 9 ]. In addition, examples of stereo-images from diff erent scientifi c disciplines (biology, paleontology, mineralogy) are provided.


34 Materials and Methods


Stereo from a single micrograph . Object-depth mapping, the foundation of one-photograph stereo-imaging, is based on a rather simple principle. It is commonly assumed that parts of an object nearer to the viewer are brighter in appearance, whereas parts of the object at greater distance from the viewer are darker [ 9 ]. Different levels of brightness and darkness are attributed to respective color codes, finally resulting in a color map of the object ( Figure 2 ). From each color code an individual image is reconstructed so that an


Figure 1 : Sample tilting technique for the generation of stereo-images and its application to electron microscopy. (a) Basic principle, (b) result (anaglyph of a foraminifera, basic photo from UCL MIRACLE).


doi: 10.1017/S1551929518000640 www.microscopy-today.com • 2018 July


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