Converting UHD HDR to SDR?

[tommy2010]

Hi there,

I'm running a 1080p Panasonic projector fed by content from Dune HD Base 3D media player and not ready to give up on it as the quality is phenomenal (scales 4K to great effect) and so I'm trying to find a solution for UHD HDR content. Here is what I learned thus far.

HDR uses the extended color gamut bt 2020 and as a result colors look muted, lacking in brightness and contrast when viewed on a non HDR HD display that uses the rec 709 gamut.

UHD blu-ray players usually can down-convert from bt 2020 to rec 709 for non HDR display users but there have been reports of the results not being too great.

This brings me consider video conversion but am stuck in finding more info. I love handbrake when it comes to video quality but unfortunately there aren't any settings when it comes to color processing. Going deeper down the rabbit hole it seems that MeGUI with AviSynth is the way to go and am hoping that someone will be able to point into the right direction or a guide that deals with color conversion. It seems that the AviSynth command "ConvertToYUY2(clip, matrix="rec709")" should convert the color matrix from bt 2020 but I believe it's not enough and some other color processing still needs to be applied for the right color, brightness and contrast, etc.

I'd appreciate any help on this subject and if someone has actually done a successful video conversion from HDR to SDR and could guide me through it then that would be even better.

Many thanks.

[Cornucopia]

First, rec2020 is not necessarily HDR (it is WCG), though HDR was built on 2020. Or rather they created the rec2100 extension to 2020 to support HDR.

Next, AFAIK, there is not yet any consumerware (free or not) that supports proper hdr -> sdr conversion.
That includes avisynth, ffmpeg, etc.

Scott

[usually_quiet]

I did a Google search and found what looks like an answer, but the method I found won't be useful for most consumers.

It appears DaVinci Resolve Studio can be used to convert from HDR to SDR, but DaVinci Resolve Studio is $299 pro software and using it for this sort of conversion requires some knowledge of color grading. See "Cross Converting HDR to HDR & HDR to SDR" at https://www.mysterybox.us/blog/2016/10/27/hdr-video-part-5-grading-mastering-and-delivering-hdr

There is a free version of DaVinci Resolve, but I have not used any version of DaVinci Resolve and don't know if the necessary features exist in the free version.

[tommy2010]

Thank you for your answers and yes it seems that there isn't a straight HDR to SDR conversion tool yet but I'm exploring the possibility of a run around. If Avisynth can be used to convert the color matrix to rec 709 followed by applying color adjustments, boosting brightness and saturation, etc wouldn't you achieve SDR that way or at least something that doesn't look so bland? Is there a guide somewhere for color correction using Avisynth?

Thanks again

[Cornucopia]

What is happening here is akin to automatic Tone Mapping, and if you have ever tried to tone map an hdr picture - without having visual feedback - you would know how complex a problem this is to even get a reasonable image much less an accurate one.

Scott

[little-endian]

@Cornucopia

The approach to get a "reasonable" image out from HDR content displayed in SDR can't be that huge of a problem as the renderer madVR clearly shows. After all, it supports that in real-time and even if not accurate to the latest coordinate of BT.709 or whatever, it should at least fit the first category of being reasonable.

The task would be to capture madVR's output and encode that with x264 for example. This way, not only the colorspace conversion but also even the necessary dithering part (only too often to be forgotten) would be taken into account.

[flashandpan007]

it may look easy in madvr, but it is a very complex problem.

[little-endian]

The underlying problem for sure and my highest respect to the author and all the ones who have contributed to the project, no question. But what I mean is that it has already been solved at least when it comes to "reasonable" results and the software required is out there.

So why not go from there and try to capture the output and feed some encoder with it?

[veresov]

HDR->SDR for Avisynth+:

http://rationalqm.us/DGTonemap.rar

[Ollie947732B]

handbrake and ffmpeg are the solutions to convert 4K HDR x265 10bit video to SDR video. find detailed guide