Re: Using flat field image

[Doug Welch <welch@physics.mcmaster.ca>]

You rescale so that the mean value of the (bias-subtracted) target 
image is the same after the division.

You *must* have a flatfield image which has not been binned in any
way to take out the pixel-to-pixel sensitivity variations. Sometimes
when the flatfield is obtained from the dome (or other non-sky
source) a well-binned correction is done to correct for the
difference in illumination of the chip by the sky and the inside
of a dome. That is, an illumination correction is one that takes
out large angular differences in response due to the difference
in the pattern of illumination across the field of view.

Cheers,
Doug

On Mon, 18 Dec 2000, Creager, Robert S wrote:

> 
> Quick (hopefully) question:
> 
> How does one divide a flat field image into the dark-subtracted target
> image?  I.E. what scaling is done before/after the division to either/both
> images?
> 
> Related question:  Should the flat field image (since it's derived from sky
> pictures) be filtered in any manner (box, ???)?
> 
> Thanks,
> Rob
>