HDR to SDR Near-Full Conversion

[jay123210599]

How do I convert HDR videos/movies to SDR, to the point where people will not notice the difference?

[microchip8]

You do tonemapping. Most people will not notice it's been converted if done right. Tonemapping is not perfect and will never be

[GeoffreyA]

Originally Posted by jay123210599

How do I convert HDR videos/movies to SDR, to the point where people will not notice the difference?

https://forum.doom9.org/showthread.p...51#post2011951

[jay123210599]

Originally Posted by GeoffreyA

https://forum.doom9.org/showthread.p...51#post2011951

But none of them will achieve the result I want?

[GeoffreyA]

Originally Posted by jay123210599

But none of them will achieve the result I want?

Use the libplacebo version. Its results are excellent and, I reckon, will solve your problem. I'll post a cleaner version of the command tomorrow, but you can use that for now; it's the same and will work. The target resolution is 1080p, which you can adjust.

Are you aiming for a bit depth of 8 or 10 bits?

Also, what about your audio? Are you downmixing or copying straight over?

[wonkey_monkey]

Originally Posted by jay123210599

How do I convert HDR videos/movies to SDR, to the point where people will not notice the difference?

If we could do that, there'd be no point in HDR in the first place.

[jay123210599]

Originally Posted by GeoffreyA

Use the libplacebo version. Its results are excellent and, I reckon, will solve your problem. I'll post a cleaner version of the command tomorrow, but you can use that for now; it's the same and will work. The target resolution is 1080p, which you can adjust.

Are you aiming for a bit depth of 8 or 10 bits?

Also, what about your audio? Are you downmixing or copying straight over?

About my HDR video: It's a clip of a 2160p HDR movie with black bars. I want the output to trim out those black bars and I'm aiming for 10 bits.

[GeoffreyA]

This script will convert the video stream, discarding audio, to 10-bit BT.709 SDR, encoding as HEVC. Place in a BAT file, collapsing the FFmpeg command onto one line, set the crop values highlighted in bold, as well as x265 settings.

setlocal
set crop=Width:Height:Left:Top

ffmpeg -init_hw_device vulkan -i INPUT -map 0:v:0 -map_metadata -1 -vf libplacebo=upscaler=spline36:downscaler=spline36:w=1920:h=-1:
                                                                       tonemapping=spline:gamut_mode=perceptual:
                                                                       colorspace=bt709:color_trc=bt709:color_primaries=bt709:range=limited:format=yuv420p10le,
                                                                       crop=%crop%:exact=true,sidedata=delete -c:v libx265 [...] OUTPUT

endlocal
pause

For my part, I prefer to add the cropping filter after libplacebo has processed everything, avoiding issues with scaling. The simplest way to get the cropping values are to open the source in VirtualDub2, add a resize filter to shrink to 1080p, and a crop filter after that. Crop the picture on a bright scene and note all numbers.

Now, where it says crop=Width:Height:Left:Top above, take your values from VD2 and substitute them. Generally, Height and Top are key. For example:

crop=1920:804:0:138

As others have noted, converting from HDR to SDR is a lossy process, and there is no one "right" way of doing it. A reasonable aim would be to match, come close to, or surpass the official 1080p version.

[Z2697]

It's not possible unless there's little to none highlight (when you playback them on non-crap HDR devices)

If the device is not HDR or crap HDR, it's likely been doing tonemapping already (or clipping which should be worse) so good tonemapping will give you similar or better looking

[wswartzendruber]

Question: Do you have control over which playback devices are used? I ask because I have found converting to HLG to work quite well. Most of the highlights are preserved on devices that can show them, yet it naturally looks like SDR when played back as such. The reason you need to control the playback is that some players absolutely suck at BT.2020->BT.709 color mapping.

[GeoffreyA]

Originally Posted by wswartzendruber

Question: Do you have control over which playback devices are used? I ask because I have found converting to HLG to work quite well. Most of the highlights are preserved on devices that can show them, yet it naturally looks like SDR when played back as such. The reason you need to control the playback is that some players absolutely suck at BT.2020->BT.709 color mapping.

If you mean in reference to libplacebo, I'm not too sure but expect it to be able, having a rich selection of settings.

https://github.com/haasn/libplacebo/...ocs/options.md
https://ffmpeg.org/ffmpeg-filters.html#libplacebo

[wswartzendruber]

Originally Posted by GeoffreyA

If you mean in reference to libplacebo, I'm not too sure but expect it to be able, having a rich selection of settings.

https://github.com/haasn/libplacebo/...ocs/options.md
https://ffmpeg.org/ffmpeg-filters.html#libplacebo

I wasn't referring to libplacebo specifically. I have written a tool set for converting from PQ to HLG:

Source: https://github.com/wswartzendruber/hlg-tools
Wiki: https://github.com/wswartzendruber/hlg-tools/wiki
Binaries: https://github.com/wswartzendruber/hlg-tools/releases

I'm not going to act like this is objectively the best way to go about things, but it does address what I believe to be the elephant in the room: 4K UltraHD discs are mastered with wildly varying levels of brightness. Fundamentally, if someone is downconverting from absolute brightness (HDR-PQ) to relative brightness (HDR-HLG and SDR), they have to know where reference white is on the PQ source. This is because the implicit definition of HDR-PQ over HDR-HLG and SDR is expanding the room between reference white and max white. And because of this, downconversion is the inverse: compressing the space between reference white and max white. If you get reference white wrong, you'll either over-compress or under-compress different brightness ranges.

[lollo2]

Originally Posted by wonkey_monkey

If we could do that, there'd be no point in HDR in the first place.

the only appropriate comment in this thread

[wswartzendruber]

Originally Posted by lollo2

the only appropriate comment in this thread

That's kind of why I proposed HLG as an alterative to SDR. Again, this depends on:

1. Correct brightness adjustment.
2. SDR playback on a BT.2020-aware player.

[GeoffreyA]

Originally Posted by wswartzendruber

I wasn't referring to libplacebo specifically. I have written a tool set for converting from PQ to HLG:

Source: https://github.com/wswartzendruber/hlg-tools
Wiki: https://github.com/wswartzendruber/hlg-tools/wiki
Binaries: https://github.com/wswartzendruber/hlg-tools/releases

I'm not going to act like this is objectively the best way to go about things, but it does address what I believe to be the elephant in the room: 4K UltraHD discs are mastered with wildly varying levels of brightness. Fundamentally, if someone is downconverting from absolute brightness (HDR-PQ) to relative brightness (HDR-HLG and SDR), they have to know where reference white is on the PQ source. This is because the implicit definition of HDR-PQ over HDR-HLG and SDR is expanding the room between reference white and max white. And because of this, downconversion is the inverse: compressing the space between reference white and max white. If you get reference white wrong, you'll either over-compress or under-compress different brightness ranges.

I think it's an interesting tool. Using HLG as an alternative to SDR hadn't occurred to me.

[lollo2]

Originally Posted by wswartzendruber

That's kind of why I proposed HLG as an alterative to SDR. Again, this depends on:

1. Correct brightness adjustment.
2. SDR playback on a BT.2020-aware player.

Makes sense. But note that the OP is a well known troll (videohelp forums are full of his non-sense) and he asked in purpose "to the point where people will not notice the difference?"

[wswartzendruber]

Originally Posted by lollo2

Makes sense. But note that the OP is a well known troll (videohelp forums are full of his non-sense) and he asked in purpose "to the point where people will not notice the difference?"

Perhaps by that he means that someone should not realize just from watching the video that it comes from a PQ source.

[GeoffreyA]

Originally Posted by wswartzendruber

Perhaps by that he means that someone should not realize just from watching the video that it comes from a PQ source.

That's what I think: that the video should be indistinguishable from the "official" SDR version.

[rwill]

Originally Posted by lollo2

Makes sense. But note that the OP is a well known troll (videohelp forums are full of his non-sense) and he asked in purpose "to the point where people will not notice the difference?"

Regarding noticing if something has been hand graded to SDR or tonemapped down from HDR, it is more or less the same concept as at which point do people notice the difference between an honest question and a troll. Some will notice right away, some will if it is pointed out to them, some will never.

[lollo2]

Originally Posted by GeoffreyA

That's what I think: that the video should be indistinguishable from the "official" SDR version.

OP meant SDR indistinguishable from HDR, that’s why he’s trolling