Users requesting WFPC2 data from the MAST archive now receive an additional data
product, a quick-look mosaic of the images from all four detectors. The new files, labeled *drz.fits,
are produced by the program PyDrizzle. The images are geometricaly corrected and have a plate scale
equal to that of the third group (usually WF3); in the absence of the third group, the plate scale of the
first group (usually PC1) is used. After an update to the pipeline, scheduled for late September, the
plate scale will be 0.1" per pixel. If an image contains only the PC1 (single group image), its native
plate scale will be used. Because Multidrizzle is run on each WFPC2 exposure independently, the program
cannot perform sub-pixel sampling or cosmic-ray rejection. DRZ files are thus intended as quick-look images,
rather than as science data products. DRZ files utilize a multi-extension FITS format, rather than the waiver FITS
format of traditional WFPC2 data products.
Please note: the units for WFPC2 drizzled images retrieved from MAST are counts per second
(vs. the other WFPC2 image products which are in units of counts). The header keyword PHOTFLAM is taken
from the first extension (usually the PC chip) of the calibrated data file.
