Space Telescope Science Institute
WFC3 Data Handbook 2.1 May 2011
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WFC3 Data Handbook > Chapter 3: WFC3 Data Calibration > 3.2 Overview of calwf3

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.
Table 3.1: Tasks in the calwf3 pipeline.
UVIS Images
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.
IR Images
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.
All Images
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.
Figure 3.1: Flow diagram for WFC3 data shown with calwf3 task names.
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:
Perform cosmic-ray (CR) rejection and combining of CR-SPLIT or REPEAT-OBS data, if necessary
Each step is described in detail in Section 3.4.
Figure 3.2: Flow diagram for CCD data using wf3ccd in calwf3.
Figure 3.3: Flow diagram for overscan-trimmed CCD data using wf32d in calwf3.
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.
Table 3.2: Types of files used as input to calwf3.
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.
All WFC3 observations, not just dithered images, need to be processed with MultiDrizzle to correct for geometric distortion and pixel area effects. Please refer to Chapter 4 for more information.
Figure 3.4: Flow diagram for IR data using wf3ir in calwf3.

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