Author Topic: The problem of green in narrowband SHO palette  (Read 758 times)

Offline Bobinius

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Re: The problem of green in narrowband SHO palette
« Reply #15 on: 2019 August 06 10:55:28 »
Dave,

Probably you are right with the histogram, I usually look what's going on and indeed there is a difference between the intensity transformation (the green pixel value is less but not zero) and a clip (which would totally delete the pixel).

For example, do you know if there is a standard protocol at Hubble for producing the images - I mean I hope that the M66 aspect that Hubble produces does not depend if Sandra from NASA who did the post-processing Saturday really loves pink hues or not. Hopefully there are some objective rules for treating the image.

 ;D she usually makes good choices.

I think it is down to the processing team, i.e. Sandra LOL

Offline Niall Saunders

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Re: The problem of green in narrowband SHO palette
« Reply #16 on: 2019 August 06 10:57:45 »
Your 'local' colour is based on your optical equipment, your local conditions, and your sky conditions as photons pass through to your OTA. So, yes, you - as the imager - have to choose how you want to represent the wavelegths of the incoming light.

You will always err in favour of 'what looks good to you'.
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chr├ętien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
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Offline Bobinius

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Re: The problem of green in narrowband SHO palette
« Reply #17 on: 2019 August 06 11:01:32 »
As Niall indicated above as we didn't start with colour in the first place it is totally down to you how much red you remove, it all depends on what looks pleasing to you
Well actually we do start with colour: Ha is a deep red, SII is a deeper red and OIII is blue-green (teal). Just an idle remark.

Yes, if you try to respect the spectral lines. But the same data when using the natural colours has very low contrast. I think that's what justified the SHO palette in the first place. And of course it would be close to impossible to visually distinguish a Ha emission zone from a S2 emission zone.

Offline Bobinius

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Re: The problem of green in narrowband SHO palette
« Reply #18 on: 2019 August 06 13:26:58 »
Your 'local' colour is based on your optical equipment, your local conditions, and your sky conditions as photons pass through to your OTA. So, yes, you - as the imager - have to choose how you want to represent the wavelegths of the incoming light.

You will always err in favour of 'what looks good to you'.

You're right Niall and I agree that there are multiple physical factors that are between the object and the final xisf or fits. However, not everything is subjective and while I agree that the colour assignment for the specific emission lines are arbitrary, once this step is completed, you have to represent correctly those photons that arrived on your sensor. It is not their fault if more of them are Ha and therefore green. When you delete them you are deleting data. I am just trying to understand how to keep my workflow as accurate as I can in order to represent the Universe as it is, not as I would like it to be. (once I assigned the false colours...) I mean, why use Colour calibration for LRGB data if "anything goes"? Why should the Pixinsight team develop new Photometric colour calibration tools if "all is in the eye of the beholder"?