Appearance of discontinuities in spectra transformed by the piecewise direct instrument standardization procedure.

Several years ago, we noted that spectra transformed by the piecewise direct standardization (PDS) method may contain discontinuities. Having noticed that the problem was a recurring one, we studied it and recently diagnosed its source. Our investigations suggest that this problem also occurs in applications of window factor analysis, evolving factor analysis, and any other procedure that uses piecewise principal component models. In this work, we report the source of the problem and illustrate it with one example. A procedure is presented for eliminating the problem that is effective in PDS pattern recognition applications. Further work is needed to develop modified algorithms suitable for calibration applications.