This page contains fringing patterns for the WFI through filter Ic/lwp (#845) and I/203-ESO879.
The images are kept as mosaic fits files.
They have been created in the following way:

  • We took I-band images of different fields (spread over a week) and corrected for bias, overscan, and flats.
  • Flatcombined the images.
  • Computed the average value and subtracted it from the image.
  • Corrected for bad pixels.

So far we do not know how variable the pattern is. The intensity varies a lot, but the shape seems to be quite stable. We plan to do more measurements in the next future to clarify this point. If you have taken WFI images in I that show a very strong fringing pattern, let us know as we could use them for this analysis. With the average fringing pattern provided here it should be possible to correct down to 2% of the sky level.

How to correct for fringing?

Fringing is an additive pattern, hence it has to be subtracted from the images after the pattern has been scaled to the actual value of the fringing in the image.

  • Measure the difference between high and low level in some well defined parts of the image (preferably at positions with large fringing).
  • Measure the difference between high and low level in the same positions in the fringing pattern.
  • Compute the scaling factor by dividing the two values and scale the fringing pattern accordingly.
  • Subtract the scaled fringing pattern from the image.