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Old 16-03-2015, 08:06 PM
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Shiraz (Ray)
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Join Date: Apr 2010
Location: ardrossan south australia
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Agree, lets not throw the baby out with the bathwater. Looks like some of the processes that Hallas used are not very sensible for high resolution imaging, but the basic idea of using dither instead of calibration to remove fixed pattern noise is very powerful. It would be great if someone has a set of dithered DSLR subs that they could stack using either full calibration or dither+stack without cal to see what happens - hope this is not too far from your original post Fred?

For comparison, I just did a test to see how effective the two stacking methods are on 30 subs of dithered mono, temp controlled data. With dither stacking I did a bad pixel removal followed by a simple average stack and no calibration at all. With standard stacking I used an average stack with bias (100 bias subs), darks at the same temperature (70 darks) and flats (100 flats). The full calibration stack image showed evidence of hot pixel effects (no outlier rejection was used) so a bad pixel map was also used to remove the odd warm pixels from the images after the initial calibration.

the results: Dither really can do the job just as well as a full calibration - left image is dither only, right image is full calibration. There is a slight brightness difference where I did not get the offsets exactly equivalent, but that's it. The SNRs from the two processes were effectively identical as measured by the sky background variance.
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Last edited by Shiraz; 17-03-2015 at 10:20 AM. Reason: better pic
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