Hot pixel: final stacking black/red lines

[ippiu]

Hi.
I usually apply dark and flat correction during live stacking.
But i think hot pixels are difficult to remove completely: so each hot pixel successfully removed, leaves a sort of "tiny black hole" that form a dark line at the end of the stacking.
And each hot pixel not successfully removed, forms a "red line" at the end of the stacking.
Is it true?
Does this happen?

Thanks

Annotazione 2020-03-12 163258.jpg (179.91 KiB) Viewed 1487 times

[admin]

Hi,

This problem is often called 'raining' noise. It's caused by the dark correction not being hundred percent exact – if you have pixel in the dark that is a bit brighter than it should be (just by randomness) then that will over correct every image frame and as the image drifts leave a dark trail in the stacked image. Normally this wouldn't be very visible, but we tend to stretch Astro images to bring out the fine detail which also pulls this sort of problem interview. The usual way to try to reduce this is to use dithering which will spread the effect around over a larger area and make it less noticeable.



Cheers, Robin

[ippiu]

Excellent explanation.

Thanks Robin

[oopfan]

Hi ippiu,

My mount is not capable of dithering. To solve the "raining noise" problem I increase exposure. Works every time.

Brian