Colour post adjustment

Questions and answers about processing in StarTools and how to accomplish certain tasks.
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LuckyEddie
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Colour post adjustment

Post by LuckyEddie »

HI, sometimes I've processed an image, thought I've finished, saved it off, and then when I've seen it on a different display or under different lighting conditions I'm not happy with the colour balance.

I can go through re-processing the image from the start with different settings in the Colour module or tweak the result in some image manipulation software but what I'd really like to do is re-open the processed image in StarTools as a non-linear image, go to the Colour module and modify it there.

The problem I have is that I can't find a combination of settings in the Colour module that don't modify the previously processed image, to act as a neutral modification starting point. Is there a way to achieve this in StarTools?

Ed
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admin
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Re: Colour post adjustment

Post by admin »

Hi Ed,

Color balancing of a stretched image is fundamentally impossible - in any software. No ifs, buts or exceptions. Color balancing has to be performed on the linear data. StarTools lets you perform this towards the end of your workflow thanks to Tracking, but this is certainly not the norm. In the background, StarTools still applies the color corrections to the linear data and then forward-propagates the result. As soon as Tracking is switched off, StarTools too, can no longer do this.

To make long story short, you should not use the Color module for the purpose of color balancing once Tracking is off, nor should you perform color corrections in any other software and expect useful (photographically correct) results!

I hope this helps,
Ivo Jager
StarTools creator and astronomy enthusiast
LuckyEddie
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Re: Colour post adjustment

Post by LuckyEddie »

Hi Ivo,

I kind of suspected something like that but thought I'd ask in case StarTools offer to attempt to reverse the stretch when loading non-linear data made a difference.

Ed
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Re: Colour post adjustment

Post by admin »

LuckyEddie wrote: Thu May 12, 2022 6:50 am Hi Ivo,

I kind of suspected something like that but thought I'd ask in case StarTools offer to attempt to reverse the stretch when loading non-linear data made a difference.

Ed
That's a good point Ed. The stretch that is being reversed in that case, is a specific sRGB stretch (so very unlikely applicable to your image unless you used that specific ~2.2 gamma stretch)
Ivo Jager
StarTools creator and astronomy enthusiast
Mike in Rancho
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Re: Colour post adjustment

Post by Mike in Rancho »

Even though, as Ivo says, it really should be color balanced within tracking with a file opened from scratch, if I open a finished stretched file (almost always an ST save though), don't turn tracking on, and go into Color, the defaults of 100% general sat and full dark+bright sat, with all else zeroed out, seems fairly neutral.

In fact I really need to pixel peep, with MaxRGB on, while toggling the before/after button in order to see any super minor changes.

I admit I have done it at times, especially for cases where for whatever reason sampling may not have set the right balance so it was done more manually, but not until after I'm all done do I realize hey -- that's too purple! Or something like that. And adding a little green bias back can often remedy an over-purple disaster. ;)
LuckyEddie
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Re: Colour post adjustment

Post by LuckyEddie »

Thanks Mike, that was excactly what I was looking for. Maybe not 'correct' but functional.
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