SEM Coloration

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Scanning electron microscopes (SEM) have always been used as cameras, to document specimens beyond the capabilities of ordinary optical microscopes. But even if the images appear “naturally illuminated”, the technology is different from optical microscopy.

Topographic images

Unlike pictures captured with a camera, SEM scans are based on particle emission rather than light – they don’t show colors. Brightness depends from the characteristics of the sample surface: while dark areas mark low secondary electron emission, bright areas are the result of high secondary electron emission. SEM scans should be considered topographic images with very close resemblance to black-and-white photographs. As a consequence of the technical limitations, SEM scans need to be post-processed to before they can be enjoyed as colorful ‘vivid’ documents.

Artefacts that may arise during the preparation or within the high-vaccuum chamber of the SEM need to be removed from the original SEM scan prior to the coloration. “In general, the coloration is the most challenging and time-consuming part of my work” says Martin Oeggerli. Nature offers plenty of details in shape and nuances of color which can’t be accurately imitated without substantial experimentation in the ‘digital darkroom’.

By adding various layers of color, pattern or appropriate shadows, Oeggerli literally ‘paints’ the original SEM scan – if necessary pixel-by-pixel. “Usually, I end up with 50+ layers and an equivalent amount of individually adapted colors before I am pleased with the result”.

The size of such images has no upper limit. Usually, they exceed 1 GB in size. Without powerful computers and sophisticated software tools the the coloration remains impossible. The aim of the artist is not to invent a science-fiction reality. “It is important to understand how nature works to create authentic visual effects.” Oeggerli likes to wrap his motifs into a capacious color-costume, “combining natural perfection with -imperfection in order to mimick the subtile variation between the individual and its conspecifics which is the raw material for natural selection and thus a very important point for my work”, explains Oeggerli with a smile.


Image at different stages during the coloration process

At first glance, the composition of a wasp compound eye looks simple. Nevertheless, the coloration was complex and took several days. Apart from the colors, the original SEM-scan lacks flares and iridiscent reflections -a characteristic feature of  the brightly colored animals- which had to be reconstructed manually. In addition, thin bristles (cream) and smallest detail between individual lenses (red) of the compound eye have carefully been worked out and give this image a much more natural look.

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