= psphotStack =

{{{psphotStack}}} is the program used to perform object detection, classification, and photometry analysis for the stack images.  The treatment of stacks is slightly different from the treatment of individual exposures in a few respects:

* a set of skycell images is processed at once in {{{psphotStack}}}, nominally all five filters `grizy`.
* both raw (unconvolved) and convolved stacks are loaded.  the raw stack is used for detection, while the convolved stack is used for photometric and morphological analysis.  '''update''': as of r33964, we are using the 'raw' images for both detection and morphological analysis (but not radial apertures, discussed below).
* objects detected in the input frames are joined across the multiple filters to define common objects.  Any object for which a sources is NOT detected in any of the frames is used to define a source on those frames (MATCHED sources).  PSF photometry is performed on the matched sources.
* for each set of exposures, psphotStack generates a set of PSF-matched images, convolved to a common PSF
* a set of radial apertures are used to measure photometry of all objects and (un-detected) matched sources.  this is done for the original convolved stacks and the PSF-matched images with full-width half-max values specified by the psphot.config key PSPHOT.STACK.TARGET.PSF.FWHM (nominally 6.0 & 8.0 pixels).

For the radial apertures, the following annulii are used (defined by psphot.config keys @RADIAL.ANNULAR.BINS.LOWER and @RADIAL.ANNULAR.BINS.UPPER):

|| annulus || 

0.96 2.72 4.16 7.04 12.0 18.56 29.76 45.68 72.80 112.80 176.88