Space Telescope Science Institute
2010 WFPC2 Data Handbook
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WFPC2 Data Handbook > Chapter 3: WFPC2 Calibration > 3.4 Post-calwp2 Processing

3.4 Post-calwp2 Processing
A number of new calibration routines were developed as part of the final close-out activities for WFPC2. Some were incorporated into calwp2, but the others were written as stand-alone Python routines. These routines are described below.
Group Header Keywords Updated: CTE_1E2, CTE_1E3, CTE_1E4
An internal Python routine (called “wfpc2cte”) in the OPUS pipeline uses Andrew Dolphin’s (2004) recipe, which is a function of star brightness, observation date, and background level, to estimate the charge-transfer losses (in units of delta magnitude) for a star at x = 400, y = 400 with intensities of 100 e, 1000 e, and 10,000 e. The program only populates these header keywords. It makes no changes to image pixel values.
Note that “wfpc2cte” calculates its own background values, which are recorded in the trailer files distributed with each dataset. It does not read the BACKGRND keywords from the image headers. (This task is not available in STSDAS.)
Header Switch: DRIZCORR
Header Keywords Updated: various
Group Header Keywords Updated: various
Reference Files: OFFTAB, IDCTAB, DGEOFILE (off.fits, idc.fits, dxy.fits)
The pipeline uses PyDrizzle to construct a quick-look mosaic of the images from all four detectors. The new files, labeled *drz.fits, contain geometrically-corrected images with a plate scale of 0.1 arcsec / pixel. (If the exposure consists of a single PC image, the native plate scale of the PC1, 0".045 is used.) pydrizzle is run on one WFPC2 exposure at a time (it should not be confused with multidrizzle which can combine several images at a time with sub-pixel sampling and cosmic-ray rejection.) The resulting drz.fits files, which are generated in the MEF format, are thus intended as quick-look images rather than as science data products.
The units for drizzled WFPC2 images retrieved from the Archive are counts per second (or DN per second). Note that all other WFPC2 image products, like the c0m.fits calibrated science data, are in units of counts, not countrate. (Always check the value of the drz.fits keyword BUNIT to verify the units.) Note that the keyword PHOTFLAM1 in the drz.fits file is taken from the first extension (usually the PC1 chip) of the calibrated data file.

Due to a software bug, most drz.fits images from the WFPC2 Static Archive have the incorrect PHOTFLAM value. This should have little impact on users since drz.fits images are not meant for data analysis. Please see the WFPC2 Web page for additional details. The PHOTFLAM values in the calibrated headers, c0m.fits, are correct.

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