On the geometry of SNV and MSC

The spectral pre-treatments known as standard normal variate (SNV) and multiplicative scatter correction (MSC) often give very similar results, and are widely regarded as exchangeable. However their geometry in spectral space is not the same, and the results of this are sometimes apparent. SNV has the capacity to induce curved structures in score plots derived from the treated spectra, whilst MSC has a tendency to produce outliers in these plots. These phenomena are illustrated with an example from a near infrared imaging camera, and explained geometrically.