Colour managed odd behaviour

I’m just wondering why I’m seeing a colour shift using Davinic Resolve Colour managed workspace as its not behaving as I would expect when switching the output between Rec709 and Rec2020. (For different delivery options.)

To visualise this more easily I created a test chart recording from a Panasonic camera which has a file flagged correct as Rec709, and should be Rec709. With the colour managed work space set as below, and the Input Colour space on the file confirmed as Rec709, all is perfect with the chart and checking the colours they match what they should be, so the red should be RGB 180,16,16 and it is, whites are also correct and it looks good on the screen.

Settins709.png (53.17 KiB) Viewed 906 times

Output all correct

Chart709.png (43.3 KiB) Viewed 906 times

If I then switch the output colour space to Rec2020, I assumed that Davinci would manage the colours and ensure that all the various different inputs were converted correctly for the resulting output, but it doesn't seem to do this. The moment I switch the output to Rec2020 colours shift, and this shown by the test chart which now isn't correct.

Chart2020.png (41.57 KiB) Viewed 906 times

As can be seen the colours have shifted quite a bit and are no longer on the target value.

If I then set the input colour space of the test chart file to Rec2020 (it hasn't changed its still Rec709) it brings everything back, and the chart is correct again.

These colour shifts are seen with normal video files which I wasn't expecting as I thought the whole point of Colour Managed was Davinci dealt with colour transformations and took all the guess work out of it?

What am I not understanding here?

From your example the shift is working as intended. Converting to another colorspace, disregarding tone mapping and other mechanisms for a moment, means altering the color values to make sure they are in the same place in the new space to put it as simple as possible.

If you keep your input values numerically the same but only tell that the colorspace is different, means you are actually moving them making them appear less or more saturated depending on if the new space is bigger or smaller.

The simplest example I know of is from Chris Brejon's blog. The correct conversion of a max green (0, 255, 0 in 8bit rgb terms) becomes something that has more red and blue and less green but the position hasn't changed meaning it's still the same color.
https://chrisbrejon.com/cg-cinematograp ... stem-aces/

Screenshot 2024-04-28 at 14.27.43.png (336.52 KiB) Viewed 558 times

Now on the actual display side, if you would be viewing the image on a display with a larger gamut than 709/sRGB with display profile management enabled in Resolve (mac only) and toggle between SDR Rec.709/2.4 and SDR Rec.2020/2.4 it should visually still look the same. But the code values would still be different as per your measurements.

Hope that makes sense.

Many thanks for your reply. I've got to the bottom of it now after reading your response and having another test.

The issue appears to be the preview in Davinci when switched to Rec.2020 which shows the colour shifts in the preview (presumably due to a Rec.2020 colour space on a sRGB monitor), it also affects the scopes which threw me into thinking it was something more low level in Davanci.

The test in the end was fairly simple, export out a Rec.2020 test chart which looks wrong in the preview in DR, drop that back on to the timeline, then switch back to Rec.709 and the Rec.2020 clip appears to be correctly converted to Rec.709 and it was spot on again in the preview. I also played the Rec.2020 clip in Media Player on Windows and this appeared to handle it okay by conforming Rec.2020 to something more appropriate, as the test chart colours were correct.

So it was the preview in Davinci causing the confusion for me, I assumed it would always conform whatever was on the timeline to something that would look more or less correct on a sRGB monitor.

So it was the preview in Davinci causing the confusion for me

That's why this...

Indeed that might help.

The other work around I found is to use the LUT generator at https://cameramanben.github.io/LUTCalc/ ... index.html and making a LUT for Rec2020 to Rec709 and adding that as the video monitor LUT in DR puts the colours back. Obviously I'm not seeing any extra colours that Rec.2020 provides on my monitor but hopefully the extra colour info when rendering out as Rec.2020 UHD will show up on the TV or other displays supporting it.

I doubt that you can grade HDR seriously without HDR monitoring.
The cheapest solution would be a Mac with a XDR display (or even an iPad). The better solution would be a recent LG OLED, connected by BM I/O and calibrated. All commercial solutions are still very expensive.

This is a great resource for everything HDR: https://daejeonchronicles.com

I doubt that you can grade HDR seriously without HDR monitoring.
The cheapest solution would be a Mac with a XDR display (or even an iPad). The better solution would be a recent LG OLED, connected by BM I/O and calibrated. All commercial solutions are still very expensive.

This is a great resource for everything HDR: https://daejeonchronicles.com

Not grading HDR, that's a step too far for me at this time . I simply wanted to maintain the extra colours from the wider gamut of log footage. UHD 4K should really use the Rec.2020 colour space rather than Rec.709.

Its a mute point I agree with many consumer and pro-consumer type cameras which seem to be stuck with Rec.709 in 4K when using normal picture profiles, I presume this is a compatibility thing, but when using those same cameras with their various log outputs, the resulting colours captured can be much bigger than Rec.709 and possibly larger than Rec.2020. I just wanted to keep this extra colour rather than shoehorn it into Rec.709 which goes back to HD days.

Its a mute point...

Fwiw, it's a 'moot' point... but I'm guessing you didn't come here for that discussion, so I'd better naff off. ;)

Its a mute point...

Fwiw, it's a 'moot' point... but I'm guessing you didn't come here for that discussion, so I'd better naff off.

Its a moot point of course if all we have is 4K already in Rec.709. If we have log footage and are grading for HDR, then we use Rec.2020 gamut already (its part of Rec.2100) and so would keep the extra colour information, this extra colour data is why HDR looks better as well as having more dynamic range.

For SDR in 4K, we can and should still benefit from the larger colour space that is contained in log footage, and the industry recommendation is to use Rec.2020 colour space with 4K, with Rec.709 being an HD thing only.

https://en.wikipedia.org/wiki/Rec._2020

Of course it is all just recommendations, but with 4K we are using the wrong recommendation if exporting at Rec.709. If we have an extra large gamut of colours from our cameras, our UHD TVs can display a larger range of colours and support Rec.2020 and the recommended standard is 4K using Rec.2020, why not get the benefit of it? The benefit of HDR "is" the extra colour space captured and using Rec.2020, but it often comes with a lot of extra complications that come from grading it properly and getting it to look right across different displays. So SDR does away with that complication, but we can still get the extra punch and benefit of the much wider colour gamut or Rec.2020.

I just wanted to keep this extra colour rather than shoehorn it into Rec.709 which goes back to HD days.

I think it's practical to understand the differences in working / perserving a larger range of information versus a deliverable. Nobody out here in the world will view an SDR Rec.2020 video, everything is pretty much expected to be Rec.709 unless it's HDR. I would recommend sticking to that as well unless you have specific deliverable requirements for specific distribuition of which you'll know that the audience will view it in that context no matter what.

When working colormanaged, choosing the simple preset HDR actually sets your working space to Rec.2020 primaries and DaVinci Intermediate log gamma so you are already perserving most of the captured data. Similarly working in DaVinciWideGamut / Intermediate achieves a similar thing but those primaries encapsulate AP1 and ArriWideGamut3 for simple reasons that have to do with math of certain color operators to prevent the image from behaving in an undesirable manner.

In both cases your project can be mastered for both SDR 709, P3 and HDR P3, Rec.2020 theoretically without too much adjustments down the line.

I just wanted to keep this extra colour rather than shoehorn it into Rec.709 which goes back to HD days.

I think it's practical to understand the differences in working / perserving a larger range of information versus a deliverable. Nobody out here in the world will view an SDR Rec.2020 video, everything is pretty much expected to be Rec.709 unless it's HDR. I would recommend sticking to that as well unless you have specific deliverable requirements for specific distribuition of which you'll know that the audience will view it in that context no matter what.

When working colormanaged, choosing the simple preset HDR actually sets your working space to Rec.2020 primaries and DaVinci Intermediate log gamma so you are already perserving most of the captured data. Similarly working in DaVinciWideGamut / Intermediate achieves a similar thing but those primaries encapsulate AP1 and ArriWideGamut3 for simple reasons that have to do with math of certain color operators to prevent the image from behaving in an undesirable manner.

In both cases your project can be mastered for both SDR 709, P3 and HDR P3, Rec.2020 theoretically without too much adjustments down the line.

Davinci Resolve has the option for SDR Rec2020 in colour managed mode, it is a perfectly valid option and is why we have it as Recommendation 2020 for 4K resolutions. I've resolved my issues now with the shifting colours thank you.

Nobody out here in the world will view an SDR Rec.2020 video

Bluray 4K uses Rec.2020 for SDR. All 4K footage on streaming services that is not in HDR are using Rec.2020.

All 4K footage on streaming services that is not in HDR are using Rec.2020.

The 2 I know of, Netflix and Amazon Prime Video are Rec.709 for SDR and P3 limited in Rec.2020 container HDR. But yes, blu-ray can be SDR P3.

All 4K footage on streaming services that is not in HDR are using Rec.2020.

The 2 I know of, Netflix and Amazon Prime Video are Rec.709 for SDR and P3 limited in Rec.2020 container HDR. But yes, blu-ray can be SDR P3.

Thanks for the update. This is only for personal/family/friends use and so I keep the best quality master and it does look stunning on the UHD TV, and we've seen a real difference between Rec.709 and Rec.2020 from log footage, obviously if shooting a grey wall it will look identical, but anything in nature the extra colors really do come across and things look much more true to life.

HDR we can take it or leave it, sometimes the 'bright bits' are just too damn bright to be comfortable to watch, and mastering HDR needs a lot of extra kit and adds more complication. So I'm quite happy with SDR @ 4K.