The computation of high-dispersion net fluxes in NEWSIPS proceeds straightforwardly with a boxcar extraction. The input data consist of the high-dispersion SI, the high-dispersion resampled flag image (SF), the background fluxes determined by BCKGRD, and the noise model file. The decision to extract the fluxes with a boxcar weighting scheme means that a rectangular extraction slit is used, giving equal weight to all included pixels except at the very ends of the slit, and that both flagged and non-flagged pixels are used. No attempt is made to exclude flagged pixels in the way that the SWET procedure does in low dispersion, because there is no modeling of the spatial profile in a boxcar extraction and hence no knowledge of the relative weight that a ``bad'' pixel ought to have within the extraction slit. To address the corruption of the flux at a given wavelength by a bad pixel(s) in the extraction slit, NEWSIPS provides a noise vector. This vector may be used as an inverse weight to evaluate the relative uncertainties of computed fluxes with wavelength.
Briefly, the processing steps involved in the boxcar extraction of a series of 1-D spectra (one for each order) from a high-dispersion SI are as follows: