STScI Logo

Hubble Space Telescope
WFPC2 Drizzle Cookbooks

WFPC2 data quality flags

Excerpted from Table 3.4 of the WFPC2 Data Handbook

Flag Definition and source
0 Good pixels
1 Reed-Solomon decoding error; e.g. data lost during transmission or compression.
2 Calibration file defect. Set if pixel flagged in any calibration file. Includes charge transfer traps identified in static pixel mask file (.r0h).
4 Permanent camera defect. Static defects are maintained in the CDBS database and flag problems such as blocked columns and dead pixels. (Not currently used.)
8 A/D converter saturation. The actual signal is unrecoverable but known to exceed the A/D full-scale signal (4095). Calibrated saturated pixels may have values significantly lower than 4095 due to bias subtraction and flatfielding. In general, data values above 3500 DN are likely saturated. On-orbit tests have shown that for WFPC2, the conversion values have remained constant; therefore, the A-to-D reference file contains only one temperature and one set (row) of conversion values.
16 Missing data. The pixel was lost during readout or transmission. (Not currently used.)
32 Bad pixel that does not fall into above categories.
128 Permanent charge trap. (Not currently used.)
256 Questionable pixel. A pixel lying above a charge trap which may be affected by the trap.
512 Unrepaired warm pixel.
1024 Repaired warm pixel.
2048 Entire chip masked out, e.g. due to WF4 bias anomaly or to exclude PC chip