Note that in Table 3.4 the pixels in the SCI images are in counts, but msarith can also operate on count rates. The SCI extensions become the inputs proper to the underlying gcombine task, and the ERR extensions become the error maps. The DQ extensions are first combined with a user-specified Boolean mask allowing selective pixel masking and then fed ino the data quality maps. The output images and error maps from gcombine form the SCI and ERR extensions of the output imset. The DQ extension will be a combination of the masking operations and the rejection algorithms executed by gcombine .
Users can supply additional masks to reject objects or regions from the science arrays.
Each output file contains a single imset along with the primary header of the original file. There are additional tasks in this package for deleting and sorting imsets, as well as tasks for addressing a specific image class within an imset. Instructions on how to use header keyword information to convert HST counts to fluxes or magnitudes. Consult the online help for more details on these tasks and packages. The apphot package allows you to measure fluxes within a series of concentric apertures.