Predefined Spectral Descriptors

 

Spectral descriptors form the bases of all models used within ImageLab. They provide the benefit of introducing basic chemical or spectroscopic knowledge into the calculation of the independent variables used for modelling relationships in images. The term "spectral descriptor" is a general term designating the specification of an independent variable. Spectral descriptors may consist of something as simple as unprocessed intensities at a particular wavelength or mass, or maybe something as complicated as a mathematical function derived from several (if not all) intensities of a spectrum. Additional background information on spectral descriptors can be found here.

Currently, ImageLab supports the following spectral descriptors:

Descriptor/
Button
Supported Spectral Types Explanation
ABL
IR, UV/VIS, THz, Raman, X-Ray Diff. Area: sum of intensities between two reference points with the baseline subtracted. The user has to specify the two reference points b1 and b2 to calculate the baseline. In order to avoid a baseline too sensitive to noise the parameter "Nb" defines the number of surrounding data points to obtain the baseline reference points.
 
ALV
IR, UV/VIS, THz, Raman, X-Ray Diff. Area: sum of all intensities between two reference points; the baseline is defined by the level of the reference point b1. In order to minimize the influence of noise in the data, the parameter "Nb" defines the number of surrounding data points used to obtain the baseline reference point. Please note that areas below the reference level are subtracted.
 
ARW
All Area: the sum of intensities between two reference points; no baseline is subtracted.
 
BBL
All The logarithm of the ratio of two peak areas (with the baseline subtracted) weighted by the area of the second peak. The baseline is calculated separately for each of the two areas. In order to minimize the influence of noise in the data, the parameter "Nb" defines the number of surrounding data points used to obtain the baseline reference point.
 
BRW
All The logarithm of the ratio of two peak areas weighted by the area of the second peak; no baseline is subtracted.
 
CEN
IR, UV/VIS, THz, Raman, X-Ray Diff. Centroid: the position of the centroid of the spectral line within the boundaries b1 and b2. The value of CEN may assume values between 0 and 1.
 
PBL
IR, UV/VIS, THz, Raman, X-Ray Diff. Peak: single intensity at a particular wavelength or mass; the baseline is subtracted. The user has to specify the two reference points b1 and b2 which are used to calculate the baseline. In order to avoid a baseline too sensitive to noise in the data, the parameter "Nb" defines the number of surrounding data points used to obtain the baseline reference points.
 
PLV
IR, UV/VIS, THz, Raman, X-Ray Diff. Peak: single intensity at a particular wavelength or mass; the baseline is defined by the level of a single reference point b1. In order to minimize the influence of noise the parameter "Nb" defines the number of surrounding data points used to obtain the baseline reference point.
 
PRW
All Raw peak: single unprocessed intensity at a particular wavelength or mass; the baseline is not subtracted. This kind of descriptor is most suitable for baseline corrected spectra.
 
RBL
IR, UV/VIS, THz, Raman, X-Ray Diff. Peak ratio: the logarithm of the ratio of two peak intensities at two different wavelengths weighted by the intensity of the second peak. The peak intensities are measured relative to a baseline which is obtained from two reference points. Please note that values of RBL are restricted to a minium or maximum value which can be set in the Preferences dialog. By default the RBL values are restricted to +/- 4.6052 (which is equivalent to a dynamic range of 1:100).
 
RLV
IR, UV/VIS, THz, Raman, X-Ray Diff. Peak ratio: the logarithm of the ratio of two peak intensities at two different wavelengths weighted by the intensity of the second peak. The peak intensities are measured relative to a horizontal baseline which is defined by a reference point (intersection of the cursor b1 and the signal). Please note that values of RLV are restricted to a minium or maximum value which can be set in the Preferences dialog. By default the RLV values are restricted to +/- 4.6052 (which is equivalent to a dynamic range of 1:100).
 
RRW
All Raw peak ratio: the logarithm of the ratio of two peak intensities at two different wavelengths weighted by the intensity of the second peak. Please note that values of RRW are restricted to a minium or maximum value which can be set in the Preferences dialog. By default the RRW values are restricted to +/- 4.6052 (which is equivalent to a dynamic range of 1:100).
 
TC
IR, UV/VIS, THz, Raman, X-Ray Diff. Significant positive correlation (level of significance = 0.01) with a positive triangle template peak, multiplied by the signal area. Please note that this descriptor is set to zero if the correlation is either negative or not significant. The signal area is calculated by subtracting the area below the baseline from the integral between the reference points b1 and b2. The height of the triangular template peak is always 1.0, its shape is controlled by the points [b1,0], [a1,1], and [b2,0].
 
TCI
IR, UV/VIS, THz, Raman, X-Ray Diff. Significant positive correlation (level of significance = 0.01) with an negative triangle template peak, multiplied by the signal area. Please note that this descriptor is set to zero if the correlation is either negative or not significant. The signal area is calculated by subtracting the area below the baseline from the integral between the reference points b1 and b2. The height of the triangular template peak is always -1.0, its shape is controlled by the points [b1,0], [a1,1], and [b2,0].

Hint: The following video explains the basic ideas behind spectral descriptors.


Last Update: 2017-Feb-18