Hot Pixel elimination?

[glend (Glen)]

I have a problem with a hot 'artifact' area on the lower edge of my sensor somehow making it through the 'cosmetics' on DSS and appearing in the final stacked image.
I thought I had this solved on my first series of narrowband test images but since shifting to a new target last night it has reappeared. Here are the details: Mono Canon 450D (Cooled), with a couple of sensor faults which I have been able to process out with dithering and DSS cosmetics when shooting with my long focal length RC08 on Eta Carinea, but which reappears when shooting the Lagoon Nebula on the wider field Skywatcher MN190. I don't think I changed any of the DSS settings but maybe I did. Field of view signal area is different, on the RC08 there is data in the 'Hot' area, but on the Lagoon, there is the black of space with a couple of stars - if this makes any difference on cosmetic processing. The dithering and cosmetic processing in DSS does remove the bad row, and the column spike above the hot spot in both my test images on different scopes.
I have attached three files from last night, excuse the quality but they had to be downsized to post here, the first is a jpg of my Master Dark (a stack of darks shot at ISO1600 at 0C), the second jpg is a single 360" sub (ISO1600 at 0C) of my Lagoon session with the MN190, showing the artifacts I have to deal with; the third jpg is taken from the final stack TIFF produced by DSS. That final stacked Light from that session (10 were stacked) still show the Hot spot at the bottom.
What have I done wrong.
The final image is the same camera test shot stack on Eta C showing how the artifacts were previously processed out, using the same Master Dark, Master Offset.

[Camelopardalis (Dunk)]

Glen, that's an interesting puzzle

If I didn't know better, I'd say it's glare from an off-axis star...what does the same region of a single sub look like?

[glend (Glen)]

Originally Posted by Camelopardalis

Glen, that's an interesting puzzle

If I didn't know better, I'd say it's glare from an off-axis star...what does the same region of a single sub look like?

Dunk the first of those Lagoon lights is a single sub, the second is the resulting stack image (of 10 subs). In the Eta C test the single subs showed the artifacts but the final stacked image did not.

Here is an example, a single sub from the Eta C test, if you look closely you can see the 'dome' around the hot pixel area. And the final processed version is in my original post below, which just shows a black dot where the hot pixel is located.

[Camelopardalis (Dunk)]

This isn't a proper answer, more of a workaround...maybe...

Try using the ROI function to crop out around the edge 10 or 20 pixels and see if that makes a difference.

IMO it can't be the darks themselves...there's not enough bright pixels in them

[glend (Glen)]

I think I might have found the problem. It appears I have a problem in my darks, as while checking each dark file I found that they did not contain any evidence of the hot pixel area, and it did show up in the darks I shot for the Eta C test. So I am redoing the darks for the Lagoon test now. This could explain why Hot Pixel detection in DSS failed to remove it. More soon.

[glend (Glen)]

The problem was traced to the Darks I was using. I had been shooting with the colour camera earlier this week, and mistakenly picked up the colour camera Darks to stack with the Mono lights in DSS. DSS doesn't make it easier, as it uses the same file naming convention, and as the subs were the same length and shot at the same ISO, it was easy to grab the wrong ones. I have now separated all the colour and mono camera files so hopefully it will not happen again. It would never had been an issue if I was not using two cameras so similiar, but so different.
If your confused about why they would be different in two Canon 450D, its because the debayered mono sensor has artifacts of the debayering process that need to be processed out and DSS does this with column repair and hot pixel elimination. Using Darks from the colour sensor it misses the artifacts and treats them as signal.


THanks to all that offered advice and assistance.

Here is the resulting test downsized for Astrobin:
http://www.astrobin.com/full/244873/0/

[rustigsmed (Russell)]

looks to have done the trick!
Looking good Glen