Color problems - My M42 is pink!

[Luca Amerio]

Hi everybody.

I'm not a PI expert, however I already tried to post-process a bunch of files, seen all the Harry's tutorials and read a lot on Light Vortex Astronomy. I should have passed the novice phase...

Nonetheless I'm having biiiiig issues with the color of this shot.
It is a M42 shot, acquired with a modified uncooled Nikon D5100.
I attach two screenshots, one right after the stretch and one after a (bit strong) HDR and LocalHistogramEq. passage.

In both figures, it's clearly see that the whole picture has a rather pinkish hue!

Fist suspected? The color calibration of course!
I used the Photometric Color Calibration module, trying both the average spiral galaxy and the G2V white reference. The process was successful, but this is the result. The difference in the two cases is negligible.

My workflow has been:

• Crop
• DBE (not a strong one, the shot has been done from a very dark location and had minimum vignetting)
• PCC
• Deconvolution (following the Light Vortex tutorial, that is using both deringing support and PSF obtained through the DynamicPSF module)
• TGV Denoise
• Masked Stretch
• HDR Multiscale Transform
• Local Histogram Equalization

I tried to increase a bit the saturation, but the result has only been to go from a "rather pale pinkish M$2" to a "very saturated pinkish M42".

What else should i do? Did i do something wrong? Did I forgot something? Do I need any more passage? Or is it an acquisition problem?

Thank you very much
Best regards
Luca

[Luca Amerio]

Second screenshot (couldn't attach both to the same message)

[pscammp]

Hmmmm,
    This is interesting, I also have recently been processing an M42 integration and I too have a pinkish result compared to using the original CC tool

If I use the old CC tool then the outer nebulosity comes out more of a grey/light blue'ish colour

Using the new PCC tool (all default except for the section regarding RA/Dec etc) I get pinkish in the outer nebula area

I believe Juan said a major tutorial was due out ref PCC but no sign of it yet !

Will be watching this thread.

Paul

[Luca Amerio]

My problem with the old CC tool is that - I think - I have very few areas without nebulosity and not enough stars to calibrate it.

Correct me if i'm wrong

[msmythers]

Luca

Could you share your image in Dropbox or some other site so others could see what they end up with? It would need to be the image just before applying PCC.


Mike

[Luca Amerio]

Hi.

Here you go:

• The image (after the DBE): https://www.dropbox.com/s/kid3jqe8stnxlwy/M42_LucaAmerio_AfterDBE.xisf?dl=1
• The modules: https://www.dropbox.com/s/kid3jqe8stnxlwy/M42_LucaAmerio_AfterDBE.xisf?dl=1
• For those with a good bandwith, the whole project (4.4GB): https://www.dropbox.com/s/gft8gntnf0lnmka/M42_LucaAmerio.rar?dl=1

[Luca Amerio]

Sorry if I bump this topic.

Recently I've been trying to solve the issue, but with little success. Can anyone give me a hint?

Thank you very much
Luca

[msmythers]

Luca

I haven't looked at the project yet but your After_DBE image has a strange issue. Looking at the image with the Statistics tool the Red channel is clipped both high and low. I'm can't speak to why this is but I would expect that this is the reason why PCC and even BN/CC are not balancing your image. As I said before I hope someone else with more knowledge will look st your issue.


Mike 

[msmythers]

Luca

I think the lack of a black background is also a problem for PCC in this case. I took your AfterDBE image, separated the channels and used the LinearFit tool with green as the reference on the R and B channels. I then combined the channels and PCC still had an issue. Normal Linked STF though looked fair so I just stretched that ran a little Curves and SCNR. Nothing else just a quick image. This is the result.

Extracting channels and the use of the LinearFit tool should not be needed with a modified DSLR.


Mike

[msmythers]

Ok Luca one more time. I looked at your project and there is nothing there that is causing the problem I see with the red channel. It's happening somewhere before post processing.

So I went back to BN/CC and decided since there is no true background(all nebula and dust) and no good white reference I would use what I thought would give a decent looking M42. All subjective and the completely wrong way of using the tools but a pink image is not nice to look at. So here is all I did. I didn't even stretch the image. Your looking at the linked STF-Auto image. So BN, CC, ColorSaturation and SCNR. No masking of background, I just saturated the color to see what the colors looked like.


Mike