Technology - the coloration part

Scanning electron microscopes 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 quite different from optical microscopy.

Unlike pictures captured with a camera, SEM scans are based on particle emission rather than light - they don’t show colors and 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. Thus, an SEM scan could be seen as a topographic image with very close resemblance to a black-and-white photograph. And as a consequence of the technical limitations, SEM scans have to be post-processed to be finally enjoyed as colorful ‘vivid’ documents.

After removing any possible artefacts from the original scan, which might have arisen during the preparation or within the high-vaccuum chamber of the SEM, the scan is ready for the coloration. “Often, 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 and appropriate shadows, Oeggerli literally ‘paints the light’, if necessary pixel by pixel. “Sometimes, I’ll end up with 50+ layers and the equivalent amount of individually adapted color range selections, before I am convinced with the result”.

The size of such images has no upper limit and exceeds 1 GB in size every now and then. “Without powerful computers and sophisticated software tools most of the images would not be possible to achieve. However, it’s not about inventing a science-fiction reality. “Most importantly, you need to understand how nature works to create authentic effects. My images need a color-costume, which combines natural perfection with -imperfection, to mimick the often very subtile individual variations provided by the raw material for natural selection”, answers Oeggerli with a smile.

Image at different stages during the coloration process

At first glance, the composition of this wasp compound eye looks pretty simple, but the coloration remained complex and lasted several days. Not only do SEM-scans lack colors, they also suppress flares and iridiscent reflections, which are key characteristics of brightly colored animals (e.g. wasps, butterflies, beetles, birds, and marine invertebrates). Smallest differences between the individual lenses (red) provide another interesting detail and were worked out very carefully.