The data quality file (.c1h) flags bad pixels; see Table 45.2 for a description of the data quality values and their meaning.
A single WF/PC-1 exposure is obtained as four images (less if fewer than four chips were read out). GEIS files use group format to keep all of the data from a given HST exposure together in a single image file. The data corresponding to each sub-image for the WF/PC-1 are stored sequentially in the groups of a single GEIS image. The header file for an image contains the information that applies to the observation as a whole (i.e., to all the groups in the image), viewable by paging the header. The group-specific (that is, chip-specific) keyword information is stored with the group data in the binary data file; group keywords are only accessible via specialized software such as the STSDAS tasks like hedit or imhead.
WF/PC-1 images are normally four-group images, groups 1-4 representing CCD chips WF1-WF4 or PC5-PC8, depending on the camera used; if only a subset of chips were read out, only a subset of groups will be present. The group keyword DETECTOR provides the identification number of the chip (1 through 8) stored in that group, regardless of the number of chips read out.