P6k Gamut Issue with LED lights

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bluematrix2

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P6k Gamut Issue with LED lights

PostSun Nov 28, 2021 5:26 pm

Hi all,

recently, we shot a video with my P6k in BRAW 12:1 — Film. We were using some heavy LED lights to create a special effect, as shown in the image.

Gamut compression on.png
Gamut compression on.png (719.3 KiB) Viewed 1064 times


As soon as I turn on the DR Color Management and disable the Gamut compression, the image becomes useless, at least for my understanding/ skill set. If I leave the Gamut compression on, the image looks quite off as well.

Gamut compression off.png
Gamut compression off.png (582.3 KiB) Viewed 1064 times


What I found on the BMD manual is:
Gamut compression: Prevents monochromatic highly saturated light sources (LEDs, neon
signs, etc.) from clipping the gamut.

I don't fully understand what has happened here and what's the best way of dealing with it. We are always using LED lights in different variations and never had this issue.

Does someone have a better understanding of this and can explain to me what has happened and how I can avoid this in the future? Furthermore, what would be the best way to turn the current footage into a useful saturated image?

Any help would be appreciated.

Many thanks
Florian
Last edited by bluematrix2 on Sun Nov 28, 2021 11:08 pm, edited 1 time in total.
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rick.lang

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P6k Gamut Issue with LED lights

PostSun Nov 28, 2021 5:53 pm

This problem was discussed in great detail years ago. Having the Gamut Compression set On is the latest solution. Usually these lights are used to emulate a nightclub vibe or theatrical lights for special effects as you have done, but you do need to have some fuller balanced lights to give your subjects some ‘white’ light. If you only have the supersaturated coloured LEDs, not sure how you’ll get this to look more ‘normal’ as your eyes would have seen the subject.

You can change settings to use the widest gamut posible and proceed from there. No need to stick with Resolve Colour Managed workflow. If this clip is part of a longer piece with more normal colour, then you might try a Colour Space Transform.

May take some experimentation.

Ursa Mini 4.6k Blue LED light looks Magenta
https://r.tapatalk.com/shareLink/topic? ... source=app

Blackmagic Pocket Camera 4K Colour Fringing and colour issue
https://r.tapatalk.com/shareLink/topic? ... source=app

Color-space aware or self-delusional RWG/Log3G10 color space
https://r.tapatalk.com/shareLink/topic? ... source=app

UM in Resolve using CST for Alexa color science
https://r.tapatalk.com/shareLink/topic? ... source=app
Last edited by rick.lang on Mon Nov 29, 2021 7:11 pm, edited 1 time in total.
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Re: Pk6 Gamut Issue with LED lights

PostSun Nov 28, 2021 7:23 pm

Are these for texture maps?

I would try using ACES and use an ACES color input transform to import but don't set a color output tramsform in the project settings. Set the output transform in a node at the end of your chain in the color page. That way you get the most data to work with in the color page.

I am curious when you shot this did the RGB histogram show the channels clipped?
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Re: Pk6 Gamut Issue with LED lights

PostSun Nov 28, 2021 8:36 pm

The images you present do not seem to be a hopeless issue, as long as none of the channels were clipped during filming. The "comp. on" image looks that it may have the information you are after. However, because of the compression (what it is designed to do) the contrast in the upper areas have been compressed/altered/reduced and other values pushed around in the manner that the compression works. To fix I would first suggest to work in the DaVinci Wide color space, not ACES. This is because it is a larger color space giving more room to push colors around. Then use the HDR panel of the DR color page to adjust to your desire by adjusting the curves in various zones. Keep in mind that additional zones can be made to the highlights and shadows. Also the RGB can be split and each dealt with in the HDR zones. This might be a lot of work but might save what you have. Otherwise it would be better to experiment with the lighting and exposure and recording making sure there is no clipping (in each channel). And I would use Rick's suggestion of adding some white lights to the mix, all as part of determining the lighting to give you your best results by trial and error.
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Re: Pk6 Gamut Issue with LED lights

PostSun Nov 28, 2021 8:51 pm

Got a .braw frame to share? It's easiest to take a look at the source and then provide advice from there.

I spent a day last week shooting on two 6K Pocket Pros plus a 12K Ursa Mini Pro in a large studio space where the entire ceiling was built out of saturated RGB LED panels augmented with Hive RGB LED COB lights. It was a pretty good test of how BMD cameras react under that type of lighting and there are no issues with gamut clipping in the footage. I think that either you have a settings issue in Resolve, or the exposure was so high that color channels have actually clipped. Share a .braw frame and we'll be able to see which is the case.
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bluematrix2

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Re: Pk6 Gamut Issue with LED lights

PostSun Nov 28, 2021 11:01 pm

Thanks all for your reply.

This helps quite a lot to get a better understand of how to deal with it and to do a better recording next time. I looked at the footage on cam and only the blue channel is clipping.

The best way of making this visible in camera on set, besides looking at the histogram and clipping channels, would be to apply a Rec.709 LUT?

I have not yet worked with ACES as far as I can tell. So need to dig into it, but I will see how far I will come with Jeffrey's tip. However, it will be published on YouTube, so color space is limited anyway...

@Jamie, sure, I guess a Still saved in .tif is what you were looking for?
Since I cannot upload a 43 MB tif file here, you can download it here: (Hope sharing an external URL is ok?) https://florian-puschmann.de/wp-content/uploads/2021/11/Gamut-Com-On_1.1.1.tif
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Re: P6k Gamut Issue with LED lights

PostMon Nov 29, 2021 12:07 am

In the raw tab of the color page in Resolve there’s a dedicated “export frame” button that will export a single BRAW frame from the BRAW clip loaded

That’s what I’m referring to. That will allow us to see exactly what you captured and diagnose from there. EDIT — yes, sharing an external link is fine.

As for ACES, it had known issues with saturated blue/magenta before version 1.3, and the new "fix" for the issue is not a reversible control, so I’d advise against using ACES if you want full manual control over how colors out of the display gamut are mapped.
Last edited by Jamie LeJeune on Mon Nov 29, 2021 5:23 am, edited 2 times in total.
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Re: P6k Gamut Issue with LED lights

PostMon Nov 29, 2021 4:20 am

The top image is acceptable to me – with gamut compression on, I’d settle with it.

Try using a Gamut Limiter node with the current gamut set to DaVinci Wide Gamut, current gamma set to DaVinci Intermediate, and limit gamut to Rec.709. This works for me, and I even use ACES.

Gamut Limiter, along with gamut compression on, should be sufficient. Else, try adding LMT Neon Suppression.

Note that the Gamut Limiter must be your first node.
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Re: P6k Gamut Issue with LED lights

PostMon Nov 29, 2021 7:54 pm

The reason why I suggested ACES is the superior input transforms.
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bluematrix2

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Re: P6k Gamut Issue with LED lights

PostTue Nov 30, 2021 8:04 pm

@Jamie, here you will find the .braw frame.

https://florian-puschmann.de/wp-content/uploads/2021/11/P6kFP_ACam001_11010929_C087_322.braw

Thanks for you help!
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Re: P6k Gamut Issue with LED lights

PostTue Nov 30, 2021 10:53 pm

Most display gamuts can't reproduce bright saturated colours. This isn't normally an issue for 'natural' images and light sources but LED's are very 'unnatural' in that way.

You would have better luck if you didn't expose the lights so bright during capture, but even in post you can see just by bringing down the exposure you get more saturated colour.

Here's your shot decoded with Video gamma and HR but no other changes:
Image

Here's the same thing but with exposure slider set to -5 to really make the point:
Image

And same thing with -5 stops of exposure slider but with gamut compression disabled:
Image

So be mindful with your exposures when capturing these bright saturated monochromatic light sources like LEDS and be aware that display gamuts in general can't do bright saturated colours. This is what gamut compression attempts to deal with and where its most useful, when they are bright within an otherwise 'well exposed scene' AND overly saturated.

-----
FYI, in general ACES uses input transforms supplied by the manufacturer or done in calibration with them - so they are usually the same. Its the RRT and ODT's that changes things.
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Re: P6k Gamut Issue with LED lights

PostTue Nov 30, 2021 11:32 pm

I was able to reproduce your settings. This was quite helpful and I can work with it.

Thanks for saving the shot! I definitely learned something.
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