WFPC2 Instrument Handbook for Cycle 11

Pipeline Processing

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The pipeline processing of WFPC2 data sets reformats the telemetry received from HST into group FITS format images, generates headers containing a large number of keywords taken from both the HST and WFPC2 telemetry streams, in addition to various STScI ground system databases, and applies the corrections described below. This calibration is done with a software module known as "CALWP2" which is written in the IRAF SPP language and is available, in identical form, to users of the STSDAS system. Therefore, off-line recalibration of observations is fairly easy, and will use the same program as the OPUS system. Documentation is available in the HST Data Handbook, and the STSDAS User's Guide.

CALWP2 performs the following operations if required by the observation:

• A-to-D correction (depending on ATODGAIN)
• Bias pedestal level removal
• Bias image subtraction (depending on the gain and mode [FULL or AREA])
• Dark image scaling and subtraction (depending on gain, serials, and mode)
• Shutter shading correction (depending on exposure time and shutter in place at the beginning of the observation)
• Flat field image correction (depending on filters and mode used)
• Population of various photometric calibration keywords

In addition, the following conditions are flagged in the Data Quality File (DQF):

• Transmission failures and other possible failures
• Known bad pixels (e.g. blocked columns)
• Pixels at or above the maximum A/D converter level (i.e. saturated)
• Bad pixels in calibration reference files