Author Topic: Blending star color in  (Read 517 times)

Offline JGMoreau

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Blending star color in
« on: 2019 July 23 06:17:55 »
Hi, how can i blend the color of stars in ?
Suggestions appreciated.
Thanks

Offline Niall Saunders

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Re: Blending star color in
« Reply #1 on: 2019 July 23 07:33:31 »
Can you expand your question?
Cheers,
Niall Saunders
Clinterty Observatories
Aberdeen, UK

Altair Astro GSO 10" f/8 Ritchey Chrétien CF OTA on EQ8 mount with homebrew 3D Balance and Pier
Moonfish ED80 APO & Celestron Omni XLT 120
QHY10 CCD & QHY5L-II Colour
9mm TS-OAG and Meade DSI-IIC

Offline JGMoreau

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Re: Blending star color in
« Reply #2 on: 2019 July 23 07:41:28 »
hi Niall, well the color is just at periphery of star images, more visibly on the brighter ones.
An artefact of my 180mm lens probably.
I would like to get this color to fill inside.
A pixel_math expression maybe ?
Other ?

Could not find a good way….

Offline ngc1535

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Re: Blending star color in
« Reply #3 on: 2019 July 23 08:29:10 »
JG,

I predict you *will not* find a good way in the current state. When the brightness exceeds a certain value, no amount of color saturation will help.
A good rule of thumb is around 0.8 . Above this value it is almost impossible to manage color in a pleasing way. So the issue is how bright the stars are relative to the chrominance information. One technique, the one I typically employ, is to use strong non-linear brightening schemes to manage the brightness of things that are important to color (to make certain they do not exceed that 0.8 brightness value). Another technique is to dim the stars below the impossible bright threshold and then recolor them from the original RGB information that is stretched in a strongly non-linear way (to keep the color). Typically this is done using a star mask. This only works if the stars are not saturated from the get go. If the stars have the high values from the originally acquired images... well...then you really have to get creative. One method is to using convolution and purposely blur the stars a little to even out the flat-topped PSF. Finally, it is possible to use HDRMT to also moderate the star values- but this one is pretty messy and tough to manage for bright stars.



-adam

Offline JGMoreau

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Re: Blending star color in
« Reply #4 on: 2019 July 23 08:36:47 »
Hi Adam, thank you for your suggestions, give me room for experimentation.
I knew it was a tough nut to crack ;)

JG

Offline JGMoreau

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Re: Blending star color in
« Reply #5 on: 2019 July 23 12:17:06 »
Answering my own question O:)
150 iterations of MaskedStretch solved the problem, putting the color nicely back into the stars.
Awesome !