M33 Triangulum Galaxy in LRGB

[Richard_]

A monochrome LRGB composition of M33 captured back in January 2024 over two nights. This was a challenging dataset to process as most of the images were taken with high cloud present, which was visible in the final stacks of each channel. There is lots of detail in M33 I could bring out, but not without bringing out the bright background halos surrounding the brighter stars, so this is a happy compromise for me.

With that being said, I'm impressed with the intensity of the hydrogen-alpha nebulosity captured with such a low integration time from a Bortle 5 zone! Would love to revisit this next year with some additional data. Basic image capture details are below, but full image acquisition details can be found on my AstroBin page: https://www.astrobin.com/lp24y7/

Breakdown of LRGB

• L (67 x 120s = 2hrs 14min)
• R (21 x 120s = 42min)
• G (20 x 120s = 40min)
• B (22 x 120s = 44min)
• Total: 4hr 20min

 

M33 LRGB

[windjammer]

>>but not without bringing out the bright background halos 

So is this because stars have not been extracted beforehand or the haloes left behind after extraction ?  Haloes after extraction can usually be (ahem) cosmetically edited out.  

[Richard_]

1 hour ago, windjammer said:

>>but not without bringing out the bright background halos 

So is this because stars have not been extracted beforehand or the haloes left behind after extraction ?  Haloes after extraction can usually be (ahem) cosmetically edited out.  

Below is my first processing attempt on the first night of imaging. After stretching you can see much more detail in the galaxy but notice the diffuse light around the bright stars at 12 o'clock, 1 o'clock, 6 o'clock and 9 o'clock positions (it's more apparent when zoomed out rather than zoomed in).

These aren't halos resulting from reflections within my imaging train, filter use etc. I've seen artifacts like this in previous images when there has been high cloud present. Sadly, the large majority of my data is affected so it was a case of holding back on the processing, or discard the data and try again (next year).

[windjammer]

mmm, I  see what you mean. I've had the same trouble - never a really clear night without a high haze (or dew on the optics) and therefore uneven patches of crud popping up, as here.  I don't know what software you have in the toolbox, but I would have a go with PI's new gradient correction process with the small scale removal knob turned up to full.  Also graxpert's new AI gradient removal model is worth a try (its a free tool if you don't have it).  I would have the stars removed before letting rip.  I would also have a go with a curves  tool to suppress the background as far as possible - you never know, the real object might just be bright enough to get away with it.  In any event the blobs at 1, 6 and 9 you could probably convincingly paint out.  I DID NOT just say that.

[windjammer]

You could also crop the frame and cut the offending glows.  Just do a close up image.  Seems a shame to waste such good material.

[Stuart1971]

That is s superb image 👏🏻👏🏻.  if not a bit of thin cloud causing the issue you mention, then  it also could be a small amount of misting up on the sensor window in the camera or on the filter, I have seen this in my own set up, not quite condensation..

[tomato]

It’s a terrible cheat but on the starless image you could clone some unaffected background over the glow.

Great image BTW.

[Richard_]

11 hours ago, Stuart1971 said:

That is s superb image 👏🏻👏🏻.  if not a bit of thin cloud causing the issue you mention, then  it also could be a small amount of misting up on the sensor window in the camera or on the filter, I have seen this in my own set up, not quite condensation..

Thanks Stuart! You know, condensation on the sensor window may be a good point as I imaged M33 two or three weeks prior to changing out the dessicant on my camera per my recent post in the QHY268M owners thread.

11 hours ago, tomato said:

It’s a terrible cheat but on the starless image you could clone some unaffected background over the glow.

Great image BTW.

Thanks Tomato! Yeah, clone stamping is always an option but one option I'm looking at is to mask off these areas and prevent from stretching compared to the rest of the background. Very challenging!

 

22 hours ago, windjammer said:

mmm, I  see what you mean. I've had the same trouble - never a really clear night without a high haze (or dew on the optics) and therefore uneven patches of crud popping up, as here.  I don't know what software you have in the toolbox, but I would have a go with PI's new gradient correction process with the small scale removal knob turned up to full.  Also graxpert's new AI gradient removal model is worth a try (its a free tool if you don't have it).  I would have the stars removed before letting rip.  I would also have a go with a curves  tool to suppress the background as far as possible - you never know, the real object might just be bright enough to get away with it.  In any event the blobs at 1, 6 and 9 you could probably convincingly paint out.  I DID NOT just say that.

Thanks for the suggestion. When creating the above image, I did try the two background extraction tools you mentioned. The pixinsight version is very creative and it worked pretty good with another image I've been working on, however, I'm struggling to use this with this image. I've watched the tutorials and read the user guide, so perhaps more practice is required. Graxpert worked excellently and dare I say produced as good as result as the gradient correct pixinsight tool with very little effort.

[Clarkey]

High humidity can cause the glow round the brighter stars. Sometimes tricky to process whatever you do.

If you create a starless version in PI, then part stretch the starless image until just before the halos appear. You can then use the GAME script to mask the background whilst stretching the galaxy a bit more. (You can also use the blend tool to add back the stars and adjust the black/white point to keep the background clean). Might be worth a go?

Edited May 31 by Clarkey