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Stereoscopic Effects


Figure 2 : Concept of object-depth mapping and related 3D imaging offered by the computer program Picolay [ 9 ]. (a) Working space window with the raw image (conodont species Apsidognathus tuberculatus ) and menu bar, (b) computed depth map of the microscopic object, (c) resulting red-cyan anaglyph (basic photo from UCL MIRACLE).


image stack is produced at the end. This stack is used for the generation of the 3D image according to a well-defined procedure [ 10 ]. In general, two semi-images characterized by different focus planes show a stereoscopic deviation, where object points of the left image do not have exactly the same positions as corresponding object points of the right image. As a consequence of this phenomenon, simultaneous viewing of both images as a stereo-pair produces a spatial effect due to the image fusion capability of the brain [ 7 – 10 ]. Concretely speaking, the brain cannot distinguish between viewing two images with different perspective of the object and watching the object itself. Step-by-step procedure . The first task is to obtain an SEM image of the object where all heights in the object are in focus. To obtain the desired large depth of field, switch to a small objective aperture and lower the specimen in the stage to create a long working distance between the specimen and the final lens [ 1 ]. Object-depth mapping can be realized with professional commercial software such as Adobe Photoshop TM , but it also can be accomplished with free computer programs like Picolay ( http://www.picolay.de ), developed by Heribert Cypionka [ 9 ]. After import of an SEM image into the working space of the program, the user must execute two main steps: (1) import of the micrograph to the results window, and (2) generation of the object-depth map. Both procedures can be easily carried out using the EDIT context menu in the menu bar of Picolay ( Figure 2a ). Production of the object-depth map enables use of the 3D context menu ( Figure 2b ), where different setups and types of stereo-images can be selected. Besides classical stereo- pairs, the user can also generate red-cyan anaglyphs and animated GIFs (“rocking GIFs”) that make special stereo viewing devices unnecessary. Intensity of the stereo effect can be varied by changing the computed rotation angle of the item or the extent of the spatial dimension in the z -direction.


36


Production of a specimen tilt-based stereo-pair with the help of an object-depth map has to be imagined as follows: Based on the depth map and its included 3D information, the program is enabled to model edges and faces of the object that are not fully visible on the electron-micrograph. For this process a specifi c image rendering procedure is used, where respective object structures are extrapolated by using related mathematical algorithms. Computer-aided reconstruction of partly visible object components fi nally allows the rotation of the object by a small angle (1 to 10°). Any increase of this rotation angle commonly results in a reduction of the model accuracy, so that angles below 5° provide the best results [ 9 ]. T ree-dimensional images created with Picolay are automatically saved in the folder containing the raw images. Animated GIFs are primarily thought of for presenta- tions in the World Wide Web, but they also can be used for Powerpoint TM slide shows and similar applications.


Results As described above, images from the SEM exhibiting large


depth of fi eld can be processed into stereo-pair anaglyphs. Figures 3 through 5 show some examples of 3D anaglyph images, which should be viewed with red-cyan glasses. Jumping spiders are several millimeters in size, and they are attractive objects for SEM examination. With the help of a 3D front view, the eyes and extremities as well as the arrangement of the sensory hairs can be studied in detail ( Figure 3 , top). By increasing the image magnifi cation, the morphology of the sensory hairs and other sensory organs (for example, lyriform organs) of tarantulas and other spiders may be observed, thereby providing a better understanding of their structural functionality ( Figure 3 , bottom). In the fi eld of paleontology, unicellular organisms that leave skeletal remains rank among the most interesting study objects. Figure 4 shows a radiolarian (genus Actinomma ) measuring between 100 and 150 µm in size. T ree-dimensional images give an impression of the shell depth.


www.microscopy-today.com • 2018 July


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