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[RCC] Tips on Open Clusters

Processing Color Calibration Beginner Request for feedback Open Cluster
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ArthurD avatar
ArthurD avatar
i All,I'm just getting started in astrophotography, and while I find a trove of information for planets and nebulas, there seems to be less about open clusters.I've just finished Tuc 47 and I find my processing a bit lacking.This is my workflow:
  1. Preprocessing (WPP) [Pixinsight]
    1. Visual inspection and removal of bad frames with Blin
    2. Local normalization, high quality settings
    3. Integration with Average and Windsorized Sigma Clipping

  2. Processing [Pixinsight]
    1. Color calibration with Spectometry (I've tried with Photometric too)
    2. Removal of background with DBE (actually fairly simple as it doesn't have any nebulosity
    3. Deconvolution with BlurXterminator
    4. Noise removal with NoiseXterminator
    5. Stretching and basic curve editing

  3. Post processing (Lightroom)
    1. Final curves and color treatment

Any tips and critique, both from image capture and processing are very welcome.
I'm specially frustrated by color calibration. I've tried both Photometric and Spectrometry and I can't get rid of some green , which should be really easy to remove (it's a one shot color camera). 

Best!
ps: clusters are underrated in astrophotography!
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Quinn Groessl avatar
Quinn Groessl avatar
SPCC should work  for the color calibration. The following video should walk through setting up what you need to use it if you haven't already. https://www.youtube.com/watch?v=mlUcrEa1YgU

Other than that, I would say that the stars themselves look pretty nice, but the background being clipped to black really hurts the image in my opinion.
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ArthurD avatar
ArthurD avatar
Quinn Groessl:
SPCC should work  for the color calibration. The following video should walk through setting up what you need to use it if you haven't already. https://www.youtube.com/watch?v=mlUcrEa1YgU

Other than that, I would say that the stars themselves look pretty nice, but the background being clipped to black really hurts the image in my opinion.

Hi Quinn

Tks for the feedback!
I've fiddle more with SPCC and I am happier with the results. The key was to make sure all the curves and sensors met the image's (I assumed it would read them from the metadata, but it doesn't) and changing the saturation parameter to bem stricter. 

Good point about the black clipping, I've adjusted and it does look better. 
Thanks! I've updated the image with the points made. 

Best
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Niels_L avatar
Niels_L avatar
I am not an expert what so ever, but it looks a bit green? I downloaded your last update (could only download the jpeg) and did a SCNR to remove the green. Maybe try it out?
Jan Erik Vallestad avatar
Jan Erik Vallestad avatar
You didn't include acquisition details regarding the sub exposures, but is the cluster blown out in the linear image? I find the stars generally too saturated and lacking of color, some parts do have a bit of a green tint to them as Niels pointed out. I would re-try the stretching process in order to not over-expose the core of the cluster and the individual stars. If you have access to it some star removal software could be helpful with this.

There is some walking noise as well and I noticed that you are using the DUO camera, try activating dither if you haven't. If you have, then you could probably adjust the settings a bit. How often to do dithering depends on the amount of frames that you have and the length of your exposures, how much you need to dither can be calculated (or probably should be in order to find the most efficient amount of pixels).

Here's a thread from AB: https://www.astrobin.com/forum/c/astrophotography/deep-sky/dithering-amount/
Here's a tool to help with the calculations: https://www.astrohowto.com/interactive-dithering-calculator/
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patrice_so avatar
patrice_so avatar
Hi 

1) As Quinn said, SPCC is a great tool. 
2) Also as he said, the baground should not be clipped. BG is never completely black. 
3) Your stars are very homogeneous in colours. I would advice to increase the saturation before stretching, or better, start with a moderate arcsin stretch before stretching the image further. 
4) I would try to be gentle on the highlights to limit the aggregation of the core of the cluster. 

Clear skies

Patrice
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ArthurD avatar
ArthurD avatar
Hi everyone. 

Tks a bunch for the feedback, this is all very useful. 
@Jan Erik Vallestad will try dithering later , the threads are great

Based on the feedback: 
* No clipping of the background
* Better stretching / curves. / masking to preserve the core without clipping
* Without the core clipping I could lighten up outer stars , the image has gained significantly more information 

I'veuploaded a final image(the original is there for comparison). 
I've learned a lot, thanks for everyone's contribution. 

Clear skies
Niels_L avatar
Niels_L avatar
uploaded a final image


Looks much better! Loving to see the progress!

I did a quick SCNR, see below.