Combining data where some FOVs have very few stars

[tomato]

I’m attempting to combine data on M31 from 3 different scope/camera setups, a RASA8/QHY268c, Esprit150/RC571c and an Altair102APO/ASI178mono. The first two have been straightforward with plenty of background stars available, however the third set up has imaged the core of the galaxy, principally to get detail on the dust ‘hooks’ that project into the core, and so by nature of the small FOV, there are very few discrete stars in the image. I’m still collecting a full set of LRGB data, but all initial attempts to combine this data have failed, with APP unable to register the stack with the other two, despite trying a range of different settings. My collaborator on this project, @Tomatobro, has collected a full set of data using his RC10/ASI1600 which is better than mine but I suspect I will have a similar problem.

Any thoughts or ideas on this? One solution would be to do a mosaic so some background stars are in the FOV, but I wondered was there anything in Pixinsight’s vast array of tools for this. I suppose I could manually align, but the data still needs to be resized to match the other images, and how would you do this?

[Paul M]

 If the data can be plate solved ('I'm guessing that's the problem, it can't be) then ASTAP has an astrometric stacking function that I've used successfully but that was for a mosaic. I'm confident it will work for any solvable data sets that fully overlap.

It does take some reading of the help files to get to grips with I found.

Edited September 3, 2022 by Paul M

[gorann]

Resizing is simple in PS. I do it kind of manually by measuring the distance between the same two points (could be stars or anything that you see in both images) in the two images (using the ruler tool in PS). Dividing one length with the other gives you the factor you can use to resize one of the images so they will be on the same pixel scale and can be aligned.

Edited September 3, 2022 by gorann

[Knight of Clear Skies]

Have you tried Registar? If you share the files I could have a quick go later to see if they will align.

[tomato]

Thanks for all of the replies and suggestions, looks like I have a way forward. I can certainly measure the distance between the ends of the two hooks to obtain a scale factor, I don't have PS but there is a resize function in APP and Affinity Photo. AP also has an image align function. When I have @Tomatobro's RC data, we'll give it go.👍

[tomato]

36 minutes ago, Knight of Clear Skies said:

Have you tried Registar? If you share the files I could have a quick go later to see if they will align.

Thanks for the offer, I'll post the images when they are available. I don't have Registar but I do have Registax and AutoStakkert. Planetary images don't usually have stars so presumably these programs use features in the image to register and align them. Maybe these programs would align and stake them?

[CraigT82]

Yeah could be possible in AS3, using the surface mode and with strategically placed alignment points