Data Quality Flags

Within science data files, the PIXELDQ flags are stored as 32-bit integers; the GROUPDQ flags are 8-bit integers. The meaning of each bit is specified in a separate binary table extension called DQ_DEF. The binary table has the format presented in Table 1, which represents the master list of DQ flags. Only the first eight entries in the table below are relevant to the GROUPDQ array. All calibrated data from a particular instrument and observing mode have the same set of DQ flags in the same (bit) order. For Build 7, this master list will be used to impose this uniformity. We may eventually use different master lists for different instruments or observing modes.

Within reference files for some steps, the Data Quality arrays for some steps are stored as 8-bit integers to conserve memory. Only the flags actually used by a reference file are included in its DQ array. The meaning of each bit in the DQ array is stored in the DQ_DEF extension, which is a binary table having the following fields: Bit, Value, Name, and Description.

Table 1. Flags for the PIXELDQ and GROUPDQ Arrays (Format of DQ_DEF Extension)

Bit Value Name Description
0 1 DO_NOT_USE Bad pixel. Do not use.
1 2 SATURATED Pixel saturated during exposure
2 4 JUMP_DET Jump detected during exposure
3 8 DROPOUT Data lost in transmission
4 16 RESERVED  
5 32 RESERVED  
6 64 RESERVED  
7 128 RESERVED  
8 256 UNRELIABLE_ERROR Uncertainty exceeds quoted error
9 512 NON_SCIENCE Pixel not on science portion of detector
10 1024 DEAD Dead pixel
11 2048 HOT Hot pixel
12 4096 WARM Warm pixel
13 8192 LOW_QE Low quantum efficiency
14 16384 RC RC pixel
15 32768 TELEGRAPH Telegraph pixel
16 65536 NONLINEAR Pixel highly nonlinear
17 131072 BAD_REF_PIXEL Reference pixel cannot be used
18 262144 NO_FLAT_FIELD Flat field cannot be measured
19 524288 NO_GAIN_VALUE Gain cannot be measured
20 1048576 NO_LIN_CORR Linearity correction not available
21 2097152 NO_SAT_CHECK Saturation check not available
22 4194304 UNRELIABLE_BIAS Bias variance large
23 8388608 UNRELIABLE_DARK Dark variance large
24 16777216 UNRELIABLE_SLOPE Slope variance large (i.e., noisy pixel)
25 33554432 UNRELIABLE_FLAT Flat variance large
26 67108864 OPEN Open pixel (counts move to adjacent pixels)
27 134217728 ADJ_OPEN Adjacent to open pixel
28 268435456 UNRELIABLE_RESET Sensitive to reset anomaly
29 536870912 MSA_FAILED_OPEN Pixel sees light from failed-open shutter
30 1073741824 OTHER_BAD_PIXEL A catch-all flag

Note: Words like “highly” and “large” will be defined by each instrument team.  They are likely to vary from one detector to another – or even from one observing mode to another.