Strange artifacts ruining pictures

[Premordial (Max)]

Canon 1300d. 180sec subs. I've noticed the artifacts (the white and blue sprinkles) before and after modding the camera.

Anyone experienced similar artifacts or know the cause? I've had the Canon for a while now. Maybe old age or some sort of fairy dust?

[TrevorW]

Did you take some flats and darks ??

[Premordial (Max)]

Only using flats and bias. Looks like I should try some darks. Cheers for the suggestion Trevor.

[rmuhlack (Richard)]

Could be hot pixels maybe? is that image a single sub, or an integrated stack? if it is just a single sub, then if you dither between subs and use pixel rejection (such as winsorized sigma clipping or linear fit clipping) during pre-processing, perhaps with subsequent cosmetic correction as well, then that may clean up the stacked frame.

[Dave882 (David)]

Yep those look like hot pixels to me. The repeated pattern is due to dithering or other movement between subs. Take darks at the same exposure/gain/temp as subs and they should disappear. And also if you dither at more regular intervals those hot pixels won’t be stacked any more.

[Premordial (Max)]

Originally Posted by rmuhlack

Could be hot pixels maybe? is that image a single sub, or an integrated stack? if it is just a single sub, then if you dither between subs and use pixel rejection (such as winsorized sigma clipping or linear fit clipping) during pre-processing, perhaps with subsequent cosmetic correction as well, then that may clean up the stacked frame.

G'day Richard, image is stacked. Dithering is every sub. Will check out your clipping suggestions for pre-processing. Thanks.

[Premordial (Max)]

Originally Posted by Dave882

Yep those look like hot pixels to me. The repeated pattern is due to dithering or other movement between subs. Take darks at the same exposure/gain/temp as subs and they should disappear. And also if you dither at more regular intervals those hot pixels won’t be stacked any more.

Hey David, dithering is every sub and I'll keep doing it. Thought I could get away without darks, but there's obviously no shortcuts to this hobby

Maybe time for a cooled cam.

Cheers.

[Premordial (Max)]

Lucky to have a few clear nights. Happy to report that including Darks have resolved the hot pixels issue. Also tested with no Darks, but upped dithering distance to > 10 pixels which also resolved the issue.

Thanks to all who provided advice. Appreciated!