Starlight Xpress SXVF-H36 - Manual (Page 14)

Handbook for the SXVF-H36 Issue 1 August 2007
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is done by using a ‘statistical’ summing technique, such as median or sigma
combining, then the warm pixels will be removed altogether. This method needs more
powerful image processing than is available in SXV_Hmf, but both AstroArt and
Maxim DL can do it.
The result of applying a median filter and contrast stretch to the raw image
Another thing to try is the summing several images for a better signal to noise ratio.
Summing can be done in the ‘Merge’ menu and involves loading the first (finished)
image, selecting a reference point (a star) then loading the second image and finding
the same star with the mouse. Once the reference is selected, you can either add
directly, or average the images together. Averaging is generally better, as you are less
likely to saturate the highlights of the picture. The signal-to-noise ratio will improve
at a rate proportional to the square root of the number of summations (summing 4
images will double the signal-to-noise), but different exposures must be used.
Summing an image with itself will not change the S/N ratio!