The detectors in both channels offer subarray readout capability; see Section 6.4.4
(UVIS) and Section 7.4.4
(IR) for full details. The UVIS channel also allows 2×2 and 3×3 on-chip binning of full-frame images. Finally, a variety of dithering patterns can be requested using the Astronomer’s Proposal Tool (APT) software. Predefined patterns have been established to address common requirements, such as sub-pixel dithering to improve PSF sampling or dithering to achieve large areal coverage while also sampling the inter-chip gap (Appendix C
). The post-observation pipeline software (see Appendix E
, the WFC3 Data Handbook
, and the AstroDrizzle
documentation) carries out appropriate calibration of data taken in all of these configurations, and offers the option of reconstructing dithered images with a drizzling algorithm. A combination of software packages in DrizzlePac
can be used to optimize the drizzling of images. If the dither pattern incorporates non-integer pixel offsets, it can effectively improve the sampling of the point-spread function (PSF). The software can also handle mosaicked images according to a set of rules or associations, rectifying them onto a cartesian pixel coordinate system.