Several composite flatfields (superflats) have been generated from all Eng. 4 flatfield observations. After removing the LED pattern, these superflats where used to identify OM bad pixels. These badpixels are real physical pixels, thus include 8x8 subpixels. In addition, some observations of extented sources, such as comets, were also used to identify low sensitivity pixels. Significant deviations from the median or average values were spotted and flagged as bad pixels. The sensitivity values associated with the badpixel are suitable for a rough quality flag but not good enough for accurate correction. This CCF is used by SAS to identify the badpixel area. The "1" in the QFLAG column in the OM source list file means that there are one or more bad pixels within the photometry aperture.
The signature of the different bad pixel types is listed below:
| type of defect | recognition |
| turn on channels | positive deviation in darkframe |
| hot CCD pixel | 8x8 subpixel positive deviation in full frame image |
| edge emission | positive deviation in full frame |
| dead CCD pixel | 8x8 subpixel negative deviation in slew flatfield |
| dead pore | negative deviation in slew flatfield |
| bad CCD pixel | any 8x8 subpixel deviation in slew flatfield |
| bad for unknown reason | any deviation |
| area of reduced sensitivity | negative deviation in slew flatfield |