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	inner (pix)	outer (pix)	inner (arcsec)	outer (arcsec
0	0.00	0.96	0.00	0.24
1	0.96	2.72	0.24	0.68
2	2.72	4.16	0.68	1.04
3	4.16	7.04	1.04	1.76
4	7.04	12.00	1.76	3.00
5	12.00	18.56	3.00	4.64
6	18.56	29.76	4.64	7.44
7	29.76	45.68	7.44	11.42
8	45.68	72.80	11.42	18.20
9	72.80	112.80	18.20	28.20
10	112.80	176.88	28.20	44.22

These have been chosen to match the apertures defined by SDSS (see ​photo profile).