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Deep sky colours


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Hi I've been imaging for a while with both a (modded)  dslr and a ZWO ASI294C.

I notice all my nebula images which I would expect to be red (which are red when using my dslr) come out an orange/brown color when using my ASi294 one shot colour camera.

I use the same processing train for both types of images.

Can anyone suggest why the colours are so different and how I could get them to match?

Heres some examples of M42 and crescent nebula taken with asi camera recently.

2022-12-15 M42.jpg

2022-12-13 NGC6888 Crescent Nebula.jpg

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I have an ASI294MC Pro too. Colour balance (calibration) will need sorting as part of the processing, but I guess you've done that given the black background? I'd have a look too but can't access the link above, will request.

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50 minutes ago, Fegato said:

I have an ASI294MC Pro too. Colour balance (calibration) will need sorting as part of the processing, but I guess you've done that given the black background? I'd have a look too but can't access the link above, will request.

Sorry, changed the link now to general access.

I process in Pixinsight, which includes colour calibration - even ran the new Spectographic Colour calibration. but get same results.

Normal operations:

  • Dynamic background extraction
  • Background Neutralisation
  • Image solve
  • Spectographic colour calibration (previously with Photometric colour calibration, but same results)
  • Noise XTerminator
  • Then Stretch before tweaking the stretched image for satruration, star size etc.

 

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I won't be able to run a full calibration tonight. I have debayered and integrated the lights and run BackgroundNeutralization. Colours look like they're probably OK. So could be a calibration issue?

One thing to note with the ASI294 is that the sensor doesn't behave well with very short exposures (not sure where the cutoff is, might be <1.5 sec), so the advice is to use flat frames of 2s or more with dark flats and not a bias. Bit of a pain, but this is what I do with it when I use it. Not sure that would affect your colours though.

integration.jpg

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Fegato, thanks,  more like the colours I'd expect so its not the images then.

Also thanks for the tip on flats will take note for future.

Will have to look at how I calibrate. I've been using weighted batch preprocessing recently, but was getting  the same results when done manually.

When I look back I've probably always had this issue with this camera. Funny that images taken with DSLR are generally OK and I work them the same way.

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Nothing wrong with the data, suggest you reset WBPP to it's default settings and try again. Not sure what the funky light leaks are but possibly filter reflections.  As Fegato said, the 294 is a picky beast and works best with minimum 3 sec flats and dark flats. But your flat master looks ok tbh and the dark master is also clean. Below is after SPCC and DBE.

 

image.thumb.png.9f17fa957ebda74c1a3749fc97bc75ed.png

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Andy/Robin, thank you so much for your kind help and for processing my data, it shown me it's not my data, but my poor processing.

After Robin's post I've been thinking hard as to what the difference is between the DSLR & ASi camera processing that I do different. Turns out its SCNR green removal. 

I've been doing a linked STF on the image after integrating (just pressing the STF button) and it was coming up very very green, so I was removing it with SCNR, but was taking far too much out. Should have been stretching in un-linked mode and then the reds come out ok, with no green cast. If I was near a wall i'd bang my head against it.

I've got a lot of past images to go back and correct now. thats Christmas holidays sorted.

As for filter leakage, that I can sort, it's not usual in my images.

Thanks Again for your help.

Alan

m42-3.jpg

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Yes, unlinked stretch is the thing. BN gets rid of the colour cast, and is obviously built in to PCC and SPCC. I normally do this after DBE (or as I'm lazy and struggle with DBE, ABE which works well for me and saves a ton of time!).

A separate point about SCNR - I learnt a trick (I think from Jon Rista's writings - website or CN post), to leave SCNR until the image is stretched. You can then look at the histogram in HistrogramTransformation and get some feedback on what you are doing. I normally find the green curve is just beyond the blue, and I do enough SCNR to just bring it back roughly in line.

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