4 The spectrum detection procedure DETSP

The spectrum detection procedure DETSP (Bratsolis et al. [1998]) takes as input an image frame from the digitized spectral plate with particular parameters for the spectral images (dispersion, length, width). The subframe overlapping can be applied to both axes (defaulted), only down the wavelength axis, or skipped altogether. The processing is carried out in four sequential stages:

${\it a.~Image~frame~preprocessing}$
The whole image frame is filtered by a sequence of median and smoothing filters. A grid of subframes is fixed on the filtered image, according to the overlapping mode.

${\it b.~Subframe~signal~processing}$
Each one of the fixed subframes is processed by applying the detection algorithm based on a signal processing method. The detected spectral positions are saved in a table format.

${\it c.~Detection~table~processing}$
There are possible double detections of spectra near the edges of neighbouring subframes. For this reason, the table of detected spectra is now processed to remove the doubling. It is sorted as well.

${\it d.~Detections~fine~adjustment}$
The signal processing approach is used again. As many subframes are fixed as the number of detected spectra. The subframes are narrower and each one includes a particular detected spectrum image. This leads to fine adjustment of the position. The adjusted position table is finally sorted.