What is the meaning of the artifact flags in the images?
The pixels in the artifact flag images are bitwise-encoded unsigned integers, each of which is the bitwise logical ‘or’ of some or none of a set of 4 possible flags. See Table 2 and the image artifact gallery at CalTech’s Pipeline and advanced data description.The flags are applied to regions of the image derived entirely from geometry based on knowledge of the detector’s orientation and (for some flags) an a priori estimate of the NUV/FUV brightness of known stars. Source brightness criteria for flagging are generous, meaning that false-positives, especially for ‘edge’ flags, are common. False-negatives are much rarer, but definitely occur with some regularity. As an example, if pixel N for an image is overlayed by an edge reflection region and is in the rim region (i.e. near the detector edge), its value is Flag(N) = 2(1 – 1) = 1 (edge condition) or 2(6 – 1) = 32 (rim condition) 1 + 32 = 33 (bit coded value for both conditions) The flag should be treated as an unsigned value. NOTE: T
