
Notes on psphot function calls within ppsub:

we have these psphotReadout varients:

* psphotReadout : ppImagePhotom.c, ppSimPhotom*, 
* psphotReadoutFindPSF : used by ppSubMatchPSFs.c, ppSubMakePSF.c, pswarpLoop.c
* psphotReadoutKnownSources : used by ppStackPhotometry.c 
* psphotReadoutMinimal : used by ppSubReadoutPhotometry.c

* psphotStackReadout : used only by psphotStack.c
* psphotForcedReadout : used only by psphotForced.c
* psphotMakePSFReadout : used only by psphotMakePSF.c

psphotReadout:
  * operates on pmFPAfile "PSPHOT.INPUT" -> convert to an input argument (filerule)
  * expects a readout at the current view, populated with a image (can create mask and variance)
  * XXX what about the headers?

  * adds a photcode to readout->analysis
  * creates a mask and optionally modifies the variance (NOTE!)
  * if needed, generates PSPHOT.BACKMDL & PSPHOT.BACKMDL.STDEV pmFPAfiles (internal)
  * optionally copies PSF model from PSPHOT.PSF.LOAD to PSPHOT.INPUT
  * detetections / sources saved on readout->analysis as PSPHOT.DETECTIONS
  * result psf goes on readout->analyss as PSPHOT.PSF
  * detection efficiency data goes on readout->analyss as DETEFF
  * copy input sources from PSPHOT.SOURCES.CMF & PSPHOT.SOURCES.TXT -> PSPHOT.DETECTIONS
  * header data goes into PSPHOT.HEADER
  * psf clump stuff goes on readout->analysis



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in ppSubMatchPSFs.c : we call psphotReadoutFindPSF to measure the PSF using sources already loaded
  (PPSUB.INPUT & PPSUB.REF)
