Can you normalize the background in DSS multi stacked images

[Ewan]

I could not think of a better way to word my question i do appologise.

I took 2 sets of subs on 2 different nights of M44, used DSS to combine & stack them using the Groups tab at the bottom, this is what i ended up with :-

As you can see there is a dark(ish) rectangle where the images are overlaid using the mosaic option in DSS, is there a way to correct the background colour to the same depth of black or as near as ?

I have tried stretching & DBE in PixInsight but no luck, or do you just not use the mosaic option but then it's very difficult to frame the object in the exact same position each night. Layers & blending in PS which i know nothing about at this point maybe an option.

I hope someone could help me as i don't really want to lose the data & thanks for looking.

[Cloudwatcher]

Yes you can blend the background to a uniform shade using PS.

Just make a seperate layer with the Magic Wand tool and then play with the Levels tool until you find a shade that you like........Simples!

[dph1nm]

I think the problem is that there are slightly (different) background gradients across the data from one or both nights. It is then not possible for DSS to match the edges all the way round by just shifting the histogram peaks up and down (which is all it is capable of doing - it cannot fit to gradients). I guess the only solution would be to produce a stack from each night separately, remove the gradients with something other than DSS, then stack the two.

I think you can also get DSS to only keep areas where there is full overlap between the two nights. This will result in a slightly smaller image, but at least it will look nicer!

NigelM

[Ewan]

Thank you both, looks like i will have to position my target dead center next time.