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This is a shot in the dark, but you seem very knowledgeable about color, video formats, and the Apple ecosystem so I thought you might have some insight into th

This is a shot in the dark, but you seem very knowledgeable about color, video formats, and the Apple ecosystem so I thought you might have some insight into this issue I'm facing recently. I'm trying to process HLG3 video files from my Sony camera and have spent far too many hours trying to figure out how different settings affect QuickTime, ffmpeg, and Davinci Resolve, among others. The biggest thing I can't figure out right now is why Davinci Resolve renders the HLG video brighter than QuickTime. If I enable 10-bit precision and Mac display color profiles for the Davinci viewer, it does seem to tap into the HDR capabilities on my MacBook and allow for full dynamic range that looks similar to QuickTime's render. However, everything is brighter, especially highlights. Do you know of any good references to better understand how HDR works on a modern Mac?

dylan604 4y ago
I got out of this particular job type just before HDR became widespread as a consumer product. Chasing color accuracy is one of the top 3 things I hate about computing only proceeded by choosing a font, and printing. I spent time in a color correction facility where we had to calibrate Sony studio reference CRTs, LCDs (or other flat panel tech), Christie projectors, and desktop monitors. I absolutely hate Hate HATE it. The external monitors being fed by a Decklink card would have to be calibrated using a dedicated instrument for each type of screen. The desktop screens would have to be calibrated by another device. At the end of the day, the client was always advised to base color decisions on the calibrated display monitors and NOT the desktop monitors. Luckily, all of this was handled by the video engineering department, and I only know as much about it from what I asked. Thankfully, it was never my responsibility! So, I guess I'm saying good luck with that! ;-) Trying to dial in all of the different display devices to match is a journey into madness. There was a time when commercial content was only ever critically evaluated on broadcast quality monitors. As web content became larger, people were less concerned about the broadcast safe and pushed values to no longer be broadcast safe so that they looked good on iPhones. All of that to say, you're not alone in your pain. Also, are you working a PC or Mac? If you're on a PC, I have zero experience with this on that platform. Fun fact (using air quotes), there was a bug in QTPlayer so that the first file you opened would display with an incorrect gamma value. When doing critical color decisions with that player, we would open some random file first, then open up the rest of the files we were interested in. Don't know if that bug is still around or not. If you're facing brightness differences between apps, my first assumption would be gamma differences between apps.
- aikinai 4y ago
  Oh okay, thanks for the response though! Yeah, this whole space is such a mess and I'm not even trying to do something at a professional level (which is why I'm using my Mac screen and not a reference monitor). There are a lot of blog posts and YouTube videos about matching Davinci, QuickTime, YouTube, etc. but so far I've only found answers for SDR. Native Mac screens have a true HDR mode built in you can see clearly when you play any HDR video in Photos, QuickTime, etc. The normal UI is capped to, I believe, 500 nits, and then HDR video unlocks up to 1600 nits. I can see my settings in Resolve are unlocking the higher brightness, so it should be triggering the MacOS HDR pipeline, but it's too bright, so I agree the gamma must be different somehow.
  - aikinai 4y ago
    I played with it a bit more just now and I'm very close! For anyone who stumbles on this thread in the future I found that in Resolve if I disable automatic color management, and set the output color space to "ST2084 500 nit", then the gamma seems to match Quicktime exactly (though I'm not a professional). It's still clearly going over 500 nits in the viewer, so I guess that's some sort of baseline that matches the "default 500 nits but go over for HDR" that Macs do. The colors are still just a bit off and I think that might be something about how Quicktime and Resolve are interpreting the Sony HLG3 colors which don't exactly match the standards. I might try some of the normalization products offered here[0] later when I get time. [0] https://xtremestuff.net/sony-and-hybrid-log-gamma-hlg/ https://xtremestuff.net/sony-and-hybrid-log-gamma-hlg/
galad87 4y ago
Because tone mapping from an high dynamic range to a standard dynamic range is not standardised, there are some recommendations, but each app uses a slightly different algorithm. Then an app might implement tone mapping for HLG, some might display it as it is on a SDR screen (HLG is supposed to be watchable even on those old SDR screens.) Or implement it mostly properly, but ignore the current screen color profile. Even for SDR, some apps don't implement Bt.1886 yet, so you might see different results.
- aikinai 4y ago
  Mentioned in a sibling comment, but actually I'm trying to edit using the HDR mode possible on native Apple screens (like the 1600 nits MacBook Pro). So I think I'm not running into any SDR mapping. It seems to be using the Mac HDR mode, but with a slightly different gamma that I don't know how to correct for.
  - galad87 4y ago
    Tone mapping is used for HDR screens too, if the screen has got less nits than the video. Anyway, probably it's something else, you will have more luck asking DaVinci Resolve developers. It could be they are ignoring the screen color profile, or they set something wrong, there are so many things that can go wrong.
3033616426 4y ago
https://www.youtube.com/watch?v=1QlnhlO6Gu8 https://www.youtube.com/watch?v=1QlnhlO6Gu8 is a great resource. IIRC, this video focuses on SDR, but this channel has many good resources. TL;DR for HDR content, you need to figure out _exactly_ which OS and which video player (or web browser) you want your content to be consumed in, and you can match that. It's difficult to achieve cross-platform color-correct output, even in SDR, and I'm not sure it'll be possible for HDR.
throwaway290 4y ago
Ifff you are sure you got everything else right, look into color space / gamma tags. Latest versions of Resolve allow to provide these tags in export settings. Sometimes you may need to use tags different than Resolve's default to make it render with correct gamma/color in QT, vimeo etc.

dylan604 4y ago

I got out of this particular job type just before HDR became widespread as a consumer product. Chasing color accuracy is one of the top 3 things I hate about computing only proceeded by choosing a font, and printing. I spent time in a color correction facility where we had to calibrate Sony studio reference CRTs, LCDs (or other flat panel tech), Christie projectors, and desktop monitors. I absolutely hate Hate HATE it. The external monitors being fed by a Decklink card would have to be calibrated using a dedicated instrument for each type of screen. The desktop screens would have to be calibrated by another device. At the end of the day, the client was always advised to base color decisions on the calibrated display monitors and NOT the desktop monitors. Luckily, all of this was handled by the video engineering department, and I only know as much about it from what I asked. Thankfully, it was never my responsibility! So, I guess I'm saying good luck with that! ;-) Trying to dial in all of the different display devices to match is a journey into madness. There was a time when commercial content was only ever critically evaluated on broadcast quality monitors. As web content became larger, people were less concerned about the broadcast safe and pushed values to no longer be broadcast safe so that they looked good on iPhones. All of that to say, you're not alone in your pain. Also, are you working a PC or Mac? If you're on a PC, I have zero experience with this on that platform. Fun fact (using air quotes), there was a bug in QTPlayer so that the first file you opened would display with an incorrect gamma value. When doing critical color decisions with that player, we would open some random file first, then open up the rest of the files we were interested in. Don't know if that bug is still around or not. If you're facing brightness differences between apps, my first assumption would be gamma differences between apps.

aikinai 4y ago
Oh okay, thanks for the response though! Yeah, this whole space is such a mess and I'm not even trying to do something at a professional level (which is why I'm using my Mac screen and not a reference monitor). There are a lot of blog posts and YouTube videos about matching Davinci, QuickTime, YouTube, etc. but so far I've only found answers for SDR. Native Mac screens have a true HDR mode built in you can see clearly when you play any HDR video in Photos, QuickTime, etc. The normal UI is capped to, I believe, 500 nits, and then HDR video unlocks up to 1600 nits. I can see my settings in Resolve are unlocking the higher brightness, so it should be triggering the MacOS HDR pipeline, but it's too bright, so I agree the gamma must be different somehow.
- aikinai 4y ago
  I played with it a bit more just now and I'm very close! For anyone who stumbles on this thread in the future I found that in Resolve if I disable automatic color management, and set the output color space to "ST2084 500 nit", then the gamma seems to match Quicktime exactly (though I'm not a professional). It's still clearly going over 500 nits in the viewer, so I guess that's some sort of baseline that matches the "default 500 nits but go over for HDR" that Macs do. The colors are still just a bit off and I think that might be something about how Quicktime and Resolve are interpreting the Sony HLG3 colors which don't exactly match the standards. I might try some of the normalization products offered here[0] later when I get time. [0] https://xtremestuff.net/sony-and-hybrid-log-gamma-hlg/ https://xtremestuff.net/sony-and-hybrid-log-gamma-hlg/

galad87 4y ago

Because tone mapping from an high dynamic range to a standard dynamic range is not standardised, there are some recommendations, but each app uses a slightly different algorithm. Then an app might implement tone mapping for HLG, some might display it as it is on a SDR screen (HLG is supposed to be watchable even on those old SDR screens.) Or implement it mostly properly, but ignore the current screen color profile. Even for SDR, some apps don't implement Bt.1886 yet, so you might see different results.

aikinai 4y ago
Mentioned in a sibling comment, but actually I'm trying to edit using the HDR mode possible on native Apple screens (like the 1600 nits MacBook Pro). So I think I'm not running into any SDR mapping. It seems to be using the Mac HDR mode, but with a slightly different gamma that I don't know how to correct for.
- galad87 4y ago
  Tone mapping is used for HDR screens too, if the screen has got less nits than the video. Anyway, probably it's something else, you will have more luck asking DaVinci Resolve developers. It could be they are ignoring the screen color profile, or they set something wrong, there are so many things that can go wrong.

3033616426 4y ago

https://www.youtube.com/watch?v=1QlnhlO6Gu8 https://www.youtube.com/watch?v=1QlnhlO6Gu8 is a great resource. IIRC, this video focuses on SDR, but this channel has many good resources. TL;DR for HDR content, you need to figure out _exactly_ which OS and which video player (or web browser) you want your content to be consumed in, and you can match that. It's difficult to achieve cross-platform color-correct output, even in SDR, and I'm not sure it'll be possible for HDR.

throwaway290 4y ago

Ifff you are sure you got everything else right, look into color space / gamma tags. Latest versions of Resolve allow to provide these tags in export settings. Sometimes you may need to use tags different than Resolve's default to make it render with correct gamma/color in QT, vimeo etc.