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4.4. Image processing
Image processing is carried out to convert the contrast
developed by the classification step into a picture depicting
component distribution. Greyscale or colour mapping with
intensity scaling is commonly used to display compositional
contrast between pixels in an image. Single wavelength
images are easy to produce but can be misleading,
since the depicted images may be biased or dominated by
variations in thickness across sample surface; multi-wavelength
images give a better representation of the sample
composition [27]. Image fusion, in which two or more
images at different wavebands are combined to form a
new image [28], is frequently implemented to provide even
greater contrast between distinct regions of a sample.
Images may be combined using algorithms based on
straightforward mathematical operators, e.g. addition, subtraction,
multiplication and division. One example is the
band ratio method, in which an image at one waveband
is divided by that at another wavelength [29,30]. Histograms
are another tool, useful for depicting pixel distribution
of components.
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