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[RCC] Fornax Cluster

Color Calibration Processing Request for feedback
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Michael Sleeman avatar
Michael Sleeman avatar

Hi together! I never tried asking for RCC, so here we go.

https://app.astrobin.com/u/MichaelCR97?i=gzp3mz#gallery

Personally I am very happy with the outcome, but different eyes see differently ;)

Only thing that still bothers me are the colors of bigger stars that are not in the center of the FOV. There seems to be a blue/red shift, due to slightly different star shapes in the R vs B subs at the edges.. Will try to fix it, but could be a tough one.

Best regards from Austria,

Michael

andrea tasselli avatar
andrea tasselli avatar
I suggest you take it down in size by a factor of two, let's say, as at the moment it is hardly viewable at full size (if not to look at the weird stars). Otherwise I'd question the colour rendering (what, just two colours?) and the use of drizzle, the stars are huge as it is, don't need to make them worse and you would loose nothing in details. Less is definitely more.
Michael Sleeman avatar
Michael Sleeman avatar

Hi,
Thanks for the feedback! :)

I did reduce the file size now.

Regarding color variation: Will look into that. Although, viewing other images of that Galaxy-Cluster - I cant really spot a bigger variety in colors in these, but maybe I dont really get what you mean 🤔 Also there is red/brownish color in NGC 1365 so I didnt completey destro the color rendering I guess?

Regarding drizzle: When I dont drizzle, the stars look like crosses though / or even like rectangles (the small ones). I though that I am downsampled + I have lots of quite good subs that were properly dithered + seeing is way better than the equipment resolution => that Drizzle would be a good idea. Can you tell me why its still not a good idea in that case? Whats the use-case of Drizzle instead?

Without Drizzle:
📷 grafik.pnggrafik.png
With Drizzle:
📷 grafik.pnggrafik.png

Thanks!
Michael

andrea tasselli avatar
andrea tasselli avatar
Well, I went to the gallery again and nothing seems to have changed. The stars are still bloated so I expected you haven't updated that image. If the stars look like crosses, in focus, then you have a problem with astigmatism which needs to be addressed I guess. If you drizzle 2x to make everything rounder then you would down-sample the final image back to the original resolution thus preserving contrast and viewability. It would also improve lateral colour so the stars off center won't look like little traffic-lights. In general your colours seem be either mainly deep yellow or light blue which I can't think to be that appealing or looking natural either, although it seems a widespread phenomenon here. My image of NGC1365 suggests there is some variety here.
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Michael Sleeman avatar
Michael Sleeman avatar

Thanks for your answer.
Yeah - I am still working on processing the version with better stars / star colors.

I have uploaded a new version now where I did a complete reprocess of the stars.
I think its way better now and the colors are also way more diverse in my opinion at least.

The “traffic light” stars in the corners are not totally gone, but way more decent now.

Let me know what you think now.

Thanks!

PS: Your NGC 1365 has some great details. Great!

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andrea tasselli avatar
andrea tasselli avatar
I think it is a much more pleasant image to look at. I'd tone down the saturation a bit as it might not do you any favour and you would have to think on a way to control those halos around the brightest stars but all told is a much improved image, more so colour-wise and a manageable one to view.
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Daemon de Chaeney avatar
Daemon de Chaeney avatar

Presumptuous as it is for someone as inexperienced as myself to give advice on something like this, but I think Andrea is correct. I’d be tempted to back off the saturation just a little but mask NGC 1365 while you do it, so it keeps its pleasant colour. You could also mask the multicoloured corner stars, invert it, then pull their chrominance and saturation down. I don’t find the flare around the bright stars offensive, and it adds a visual cue plus some drama, but if you’re sensitive about the complaints of others it’s be easy to clone stamp the flare away in the starless image. However, bare in mind that I don’t know much about anything and could be talking complete rubbish.

Overall I like it quite a lot and the problems seem pretty minor and for the most part, just matters of taste. I’d also point out that too much saturation is very common when you’ve looked at an image too long. Your brain corrects the colours out. It pays to leave it alone for half a day and look at it again later.

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Michael Sleeman avatar
Michael Sleeman avatar

Thanks for the feedback! :)

New version is online => reduced star halos (deliberately not totally removed though), less saturation and no more traffic-light stars (as far as I can see).

andrea tasselli avatar
andrea tasselli avatar
Better, way better. Thanks.
Daemon de Chaeney avatar
Daemon de Chaeney avatar

What method did you choose to tone down the star haloes Michael? You’ve made a delicately balanced job of it

Michael Sleeman avatar
Michael Sleeman avatar

I did a complete reprocess of the image (of course re-using a lot of steps).
What helped by far the most for reduced star halos was that i ditched the MaskedStretch as I realized that it stretched the star halos way more then e.g. GHS or HT did.

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Habib Sekha avatar
Habib Sekha avatar

@Michael Sleeman congratulations! A very nice IOTD.