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Old 09-06-2018, 07:41 AM
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codemonkey (Lee)
Lee "Wormsy" Borsboom

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Colour management in PixInsight

I've been having some issues with colour management in PixInsight recently. I've got a newish mac that I'm doing my processing on and it has a DCI-P3 display which is relatively wide gamut.

I haven't done much imaging since getting this new computer so I only noticed the issue in my recent image of NGC 5078.

The problem is that when I view the image in PixInsight it looks fine, but when I export the image it looks noisy and posterized in both Preview and Chrome. It looked so terrible that when I first saw the image I uploaded to Astrobin I panicked and deleted it... it looked bad. I ended up changing my processing so that it just looked not great instead of terrible but in doing so compromised the image.

My workflow was basically to process the image without a profile, then once I was done with it use ICCProfileTransformation to convert it to sRGB 2.1 When saving the image I've tried both embedding the profile and not as I read that historically some browsers had bugs when any profile was embedded and that they work best if you have it untagged but in sRGB.

I've also tried converting the image to my monitor's profile using ICCPT and then saving the image with that profile. When I do that it looks perfect in Preview.

I've enabled colour management and colour proofing in PI and still it's fine inside PixInsight but bad outside of it. Colour proofing is set up to use sRGB 2.1, with BPC. Proofing intent is perceptual.

So the image looks fine in PI. It looks fine when I save the image and then reopen it in PI. It looks bad in Preview and in Chrome. I believe Chrome is now colour managed and Preview definitely is... for those not familiar with Preview on mac it's the standard image viewer and it too has soft proofing options built in. I now have no confidence at all in what other people might be seeing.

I've uploaded a comparison to Astrobin -- you may need your monitor brightness turned up relatively high to appreciate the full difference. The comparison was made by exporting the image once with an sRGB profile and once with my monitor's profile and then opening them up side-by-side with Preview.

I should also mention that the monitor is calibrated using a Spyder.

Any help would be much appreciated.
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Old 09-06-2018, 08:40 PM
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RickS (Rick)
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Hi Lee,

Do you have access to a copy of Photoshop? It does its own colour management and I think it's probably safe to assume that it will get it right (though it will depend on the monitor profile being correct...)

I get some inconsistency between screens, systems and software packages but I generally find that the same images displayed in Photoshop and PixInsight look very similar. That's on Windows but I'd hope that Mac would be the same.

You can't process "without a profile." You're probably using the monitor profile for the image colour space which is not ideal. You should have the correct monitor profile set and use a device independent profile as the default RGB profile. I mostly use AdobeRGB since it matches the gamut of my main monitor and sRGB is too limited.

Cheers,
Rick.
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Old 10-06-2018, 10:45 AM
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codemonkey (Lee)
Lee "Wormsy" Borsboom

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Thanks Rick, appreciate the help.

Unfortunately I no longer have Photoshop... I was using CC for a while but I canned the subscription because I did 95% of my processing in PixInsight and felt the cost didn't justify the expense for the remaining 5%.

I expect differences between devices but on the same device, with software that's all supposed to be colour managed, I expect consistency. Makes it very tough for me to know how to process my images... which one is "right" ?

The images were processed without having been assigned a profile until the end, so if I select the source image in ICCPT it'll say the source profile is "<* None *> (Name of my monitor profile here)".

Last edited by codemonkey; 10-06-2018 at 01:33 PM.
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Old 10-06-2018, 07:48 PM
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Lee,

In a perfect world, or even just a reasonable one, I agree you would expect the same colours on the same computer

Here are some useful links if you want to check if an app is doing colour management correctly:

http://petapixel.com/assets/uploads/2012/06/S2fzq.jpg - if the car is purple then colour management is broken

http://www.color.org/version4html.xalter - also checks for v4 ICC profile support

Unfortunately, this stuff is often hard to get right... and even if you do it won't help if somebody is looking at your image on a browser without colour management and an unprofiled CRT screen

Cheers,
Rick.
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Old 12-06-2018, 06:35 PM
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codemonkey (Lee)
Lee "Wormsy" Borsboom

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Thanks Rick :-)

My screen shows a yellow car and a (colour-wise) seamless landscape when viewing with Chrome, so it seems Chrome is doing its job.

You're right of course in that it doesn't matter what I see if everyone else's monitors aren't properly managed, but the best I can do is get it right when viewed with a calibrated screen.

I'm wondering whether I would have had the same issue if I had processed the images in sRGB, or maybe Adobe RGB from the beginning.
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Old 12-06-2018, 06:45 PM
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Quote:
Originally Posted by codemonkey View Post
I'm wondering whether I would have had the same issue if I had processed the images in sRGB, or maybe Adobe RGB from the beginning.
I think it's still a problem though perhaps not as big, Lee. When I try to leave the background level a bit higher to show subtle faint fuzzies I get an image that looks really great on my big, calibrated screen. I copy it to my laptop and it looks like crap. Then I compromise and bring the background down a little and I'm never completely happy with it because I know how it could look under better conditions...

Cheers,
Rick.
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