Black marks on images

[Startraveller]

Hi guys,

The issues never seem to end for me it seems. All of my images, whether LRGB/SII/OIII seem to have black spots everywhere; Ha doesn't seem to have this issue, not to that extent anyway. I've tried processing my images without darks and with darks, and the problem persists. I'm attaching a couple of XISFs of M31 here (64x30s frames at Gain 300, Offset 50 in R channel): https://drive.google.com/open?id=1H6JPMMc8C3C6iUxHBGIhcFquPnEtmzhl. I tried altering the sigma clipping parameters and tried Linear Fit clipping; reducing the sigma clipping values works to an extent, but I lose a lot of detail as expected. I've also tried different rejection parameters + no rejection for my darks integration (have taken a new set of these just a day ago) with no luck. Not really sure what else to do; would appreciate any advice.

Cheers

[RickS]

I took a quick look at the two XISF files on my laptop and didn't see anything obviously wrong?  I'll take a closer look on a better screen tonight.

How large are the spots? If they are caused by cold pixels you could run CosmeticCorrection with Autodectect on the subs before integrating.  I can't think of any obvious reason why you'd get cold pixels in LRGB/Sii/Oiii and not Ha though...

Cheers,
Rick.

[Startraveller]

I took a quick look at the two XISF files on my laptop and didn't see anything obviously wrong?  I'll take a closer look on a better screen tonight.

How large are the spots? If they are caused by cold pixels you could run CosmeticCorrection with Autodectect on the subs before integrating.  I can't think of any obvious reason why you'd get cold pixels in LRGB/Sii/Oiii and not Ha though...

Cheers,
Rick.

Thanks Rick, would appreciate your insight. Not sure if I'm pixel-peeping to be honest! It's a lot more pronounced once I run DBE due to the contrast enhancement. I've added another example to the drive link, this time of IC 1805 in OIII: https://drive.google.com/open?id=1H6JPMMc8C3C6iUxHBGIhcFquPnEtmzhl. I've tried CC before but it didn't do much. Will have another go at it and see.

[Startraveller]

Just ran CC prior to registration with Auto Detect, cold pixel at value of 2.0 and it worked! Will try it on G and B frames and see if it has the same effect.

[RickS]

I can see what you mean in the IC 1805 image.  I don't think it looks terrible but removing it would be an improvement.