calwf3 uses separate paths for processing UVIS and IR images, as listed in
Table 3.1.
calwf3 automatically calls the appropriate tasks, but each may be run separately if the user desires some variation from the normal processing.
wf3ccd and
wf32d are used for processing UVIS images, while IR image processing is done with
wf3ir. The
wf3rej program is used for both UVIS and IR images to combine multiple exposures contained in a
CR-SPLIT or
REPEAT-OBS set. Fig. 3.1 shows the
calwf3 flow of data and the decisions made.
wf3ccd first subtracts the bias and trims the overscan regions from the image. If an associated set of UVIS
CR-SPLIT or
REPEAT-OBS images is being processed, all of the overscan-trimmed images are sent through
wf3rej to be combined and receive cosmic-ray rejection. The resulting combined image then receives final calibration with
wf32d, which includes dark subtraction and flat-fielding. If there are multiple sets of
CR-SPLIT or
REPEAT-OBS images in an association, each set goes through the cycle of
wf3ccd-
wf3rej-
wf32d processing.
All individual IR images are processed with wf3ir. If an association of IR
REPEAT-OBS images is being processed, the calibrated images are combined into a single product using
wf3rej. If there are multiple sets of
REPEAT-OBS images in an association, each set goes through the cycle of
wf3ir-
wf3rej processing.
During automatic pipeline processing, MultiDrizzle follows
calwf3. All calibrated images are corrected for geometric distortion correction and associated sets of dithered images are combined into a single product. See
Chapter 4 for more information.
The individual UVIS processing steps performed by wf3ccd and
wf32d are shown in Figures
3.2 and
3.3, respectively. The reference files needed for each step and the calibration switches controlling them are also listed. The calibration steps are as follows:
Individual IR processing steps performed by wf3ir are shown in
Figure 3.4, along with the names of reference files and calibration switches. The steps are as follows:
Detailed descriptions of each calibration step are given in Section 3.4. In general, the first nine steps - through conversion to count rates - are applied independently to each readout of the IR MultiAccum exposure stack. The up-the-ramp fitting processes then produces a single image representing the best-fit count rate for each pixel. The final two calibration steps are then applied to that single image, as well as to each read of the MultiAccum stack.
calwf3 exists within
STSDAS in the
hst_calib.wfc3 package and is run like any other
IRAF or
PyRAF task. The input to
calwf3 can be given either as an association table name with the “
_asn” suffix, a
single uncalibrated image with the “_
raw” suffix, or a
CR-SPLIT or
REPEAT-OBS sub-product with the “_
crj” suffix (see
Chapter 2 for a description of sub-products and product suffixes).
Table 3.2 gives a summary of the input file types. For a given input association file,
calwf3 will process all exposures listed in the input
asn file, as appropriate for the exposure, including all intermediate products referred to as sub-products. An individual exposure would be run through the entire process when the input file is a
raw file. Finally, if the root name of any sub-product is given,
calwf3 will search the current directory for an association table that contains the given root name, determine which exposures are involved in producing that sub-product, and process all those exposures as necessary.
While both CR-SPLIT and
REPEAT-OBS exposures from an association get combined using
calwf3, dithered observations from an association do not.
MultiDrizzle must be used to create a dither-combined product.
