Color (and 3D) for Scanning Electron Microscopy

Christophe Mignot Digital Surf , 16 rue Lavoisier , 25000 Besançon , France

Abstract: Colorizing images and representing them in 3D are common practices in many fi elds of science and industry. Automation of these processes is now bringing new presentation possibilities to scanning electron microscopy (SEM). Here, we discuss various methods used to bring micrographs to life and make details contained within them easier for the human eye to comprehend. These include stereophotogrammetry, refl ectometry (“shape from shading”), and a new technique for adding color to objects that soon could make fl at, gray SEM images a thing of the past.

Keywords: scanning electron microscopy (SEM) , colorization , 3D reconstruction , SEM image processing , SEM image analysis

Introduction T e scanning electron microscope (SEM) is widely used in

various fi elds of industry and science because it is one of the most versatile imaging and measurement tools. Images produced are particularly appreciated for their high depth of fi eld and excellent image resolution, both orders of magnitude better than light microscopy. However, images provided by the SEM are black and white, and single images contain information in only two dimensions. Of course grayscale images from an SEM are normal since this technology forms images with electrons instead of photons of visible light. Yet color is something important to us humans, and not just from an aesthetic point of view. For millions of years perception of color helped our ancestors to survive, for example by allowing them to distinguish a ripe fruit hidden amongst the green leaves of a tree. Color helps our brain to diff er- entiate and identify objects. T us our brains rely on color (and stereoscopic vision) to correctly perceive objects. When it comes to viewing the nanoscopic world, researchers spend hours of their precious time manually “colorizing” SEM images in order to more clearly communicate their fi ndings to other humans.

But that could soon change. T anks to the increasing power of computer soſt ware and computer graphics, the technology surrounding electron microscopes is gradually moving toward both color and 3D. Of course, whether color is applied manually or semi-automatically, the researcher has a responsibility not to cause misinterpretation of the data. Applying colors that were not present in the original image can change the viewer’s impression of the data, so the original image always should remain available to the viewer. T is article describes how color (and 3D) can be added to SEM images using both traditional techniques and modern computer methods. Note: scale bars have been eliminated from some images in this article in order to concentrate on the image processing.

Colorization Methods

In an SEM image, the signal intensity at each pixel corresponds to a single number that represents the proportional number of electrons emitted from the surface at that pixel location. T is number is usually represented as a grayscale value, and the overall result is a black-and-white image. Of course, color can be used to encode existing SEM images with extra information coming


Figure 1 : SEM images using the BSE signal from a fl at-polished specimen containing several mineral phases. (a) Raw image in grayscale. (b) False color image where a color was arbitrarily assigned to each gray level. (c) Mathematically corrected image where each color represents a different mineral phase. Original image courtesy of the School of Geosciences, University of Edinburgh.

doi: 10.1017/S1551929518000482 • 2018 May

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