Biomedical Engineering Reference
In-Depth Information
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Fig. 5.7. Light shaded (left) and colour scale (right) images of carbon nanotubes. The light shaded
image typically looks more photorealistic than the colour scale image, and helps the viewer to
visualize the shape of features more easily.
5.2.3 Shading
One other option to enhance contrast and aid interpretation of AFM images is image
shading. This routine applies an artificial shading filter to the data, and results in higher
contrast, and a more photorealistic image, at the expense of height information. The
position and intensity of the light shining on the AFM image can be changed.
Light shading often helps visualize the smallest, high-frequency structure on a surface.
The shape of image features is also often easier to appreciate in light-shaded images
(Figure 5.7).
5.2.4 Three-dimensional views
AFM height data is inherently three dimensional (3-D). However, the standard method
of rendering AFM data shows a two-dimensional (2-D) image, using a colour scale to
represent height information. This is not a normal way for humans to see shapes, and can
make interpretation difficult. In particular, for viewers unused to AFM data, it can be
difficult to determine which features are higher than others, etc. One way to overcome
this is to render the height information as a pseudo-three-dimensional image.
This procedure is very quick and easy to implement with modern computers. Three-
dimensional rendering has the effect of making the height information in the image
simpler to understand. This is typically done in one of two ways; by maintaining
the height colour scale, or including the effect of an imaged light source to illuminate
the sample topography (similar to the shading discussed above for 2-D images). Main-
taining the colour scale can make feature height interpretation simpler, while simulation
of light source tends to highlight small features and texture on the sample topography.
This latter method is somewhat more naturalistic. Finally, it is also possible to combine
these two techniques, by height-colouring
and
lighting the topography. The choice of
rendering, like choice of colours, is highly subjective, and 3-D images are very often
used for 'artistic' or publicity purposes. However, in some cases such techniques really
enhance the interpretation of the height data. Some examples of pseudo-three-dimensional
renderings are given in Figure 5.8. In addition, it is also possible to produce true three-
dimensional images with some packages. These typically require the viewer to wear
