To get the (uncalibrated) total flux registered by the MIDI detector as a function of wavelength, i.e. the spectrum F, one does the following. 
f=midigui() ; Select a photometry file
spawn,getenv('vltiCbin')+'/oir1dCompressData "'+f+'" '+getenv('prismhmask')+' out'
d=oirgetdata('out')
indext=where(d.tartyp2 eq 'T ')
indexs=where(d.tartyp2 eq 'S ')
plot,total(d(indext).data1-d(indexs).data1,2)