Emulating MadVR's HDR to SDR tonemapping using FFMPEG

[damian101]

Originally Posted by SpasV

Thank you for the post.
The CL generates 3840x2160 rawvideo. If 1920x1080 is needed instead, add one more resizing filter:

format=yuv420p,zscale=s=1920x1080

Resize before tonemapping to speed tonemapping up a lot.

[Anuskuss]

Is there an alternative for when zscale isn't available?

[huhn]

try libplacebo

[Anuskuss]

Originally Posted by huhn

try libplacebo

And what if that's not available either (this is not a hypothecial question)?

[huhn]

i don't know a 3rd thing that act as a scaler in ffmpeg.

[manolito]

If you are not sold on FFmpeg and AviSynth+ is an alternative for you, then you can try DGHDRtoSDR by Donald Graft.

Good luck
manolito

[Anuskuss]

Thanks for the tips but neither AviSynth+ nor DGHDRtoSDR are suitable alternatives - I need to use ffmpeg. In the end I decided to go for OpenCL:

ffmpeg -i hdr.mp4 -vf format=p010,hwupload,tonemap_opencl=tonemap=mobius:format=nv12:m=bt709:p=bt709:r=tv,hwdownload,format=nv12 thumb-%06d.jpg

The colors are not perfect but better than doing no color conversion at all. If someone knows an ffmpeg filter which improves upon this please let me know.

[GeoffreyA]

Originally Posted by Anuskuss

The colors are not perfect but better than doing no color conversion at all. If someone knows an ffmpeg filter which improves upon this please let me know.

I gave it a go and managed to get improved results:

ffmpeg -init_hw_device opencl -i HDR.mkv -vf hwupload,tonemap_opencl=tonemap=reinhard:param=0.1:desat=0:format=nv12:t=bt709:p=bt709:m=bt709:r=tv,hwdownload,format=nv12 SDR.mp4

While not perfect, it is not too far from the zscale/tonemap version that I use:

ffmpeg -i HDR.mkv -vf zscale=t=linear:npl=291,format=gbrpf32le,zscale=1920:-1:f=spline36,tonemap=reinhard:param=0.6:desat=0,zscale=t=709:p=709:m=709:r=limited:dither=error_diffusion,format=yuv420p,sidedata=delete OUTPUT

If it's too dark, raise "param" a little at a time. Another problem is that the brightness fluctuates per scene: there is a "threshold" parameter but I didn't test it.

[manolito]

Originally Posted by Anuskuss

Is there an alternative for when zscale isn't available?

I still do not understand why zscale is not available when you use a plain vanilla current version of FFmpeg. Could you upload a short sample of your source file and specify the desired target size so forum members could do some experimentation?


Cheers
manolito

[Anuskuss]

Originally Posted by manolito

when you use a plain vanilla current version of FFmpeg

I'm using a fork of ffmpeg called Plex Transcoder which is used by Plex (among other things) for thumbnail generation. In it's default state it will create washed out thumbnails for HDR content so I hijacked the command and inserted the OpenCL tonemap filter.

On my desktop I can just do zscale+tonemap which looks way better of course. Maybe someday I'll investigate how the thumbnails are stored on disk and replace them myself, although that sounds tedious and like something I'll eventually forget to do.

[GeoffreyA]

ffmpeg -init_hw_device opencl -i HDR.mkv -vf hwupload,tonemap_opencl=tonemap=reinhard:param=0.1:desat=0:format=nv12:t=bt709:p=bt709:m=bt709:r=tv,hwdownload,format=nv12 OUTPUT

Not perfect but an improvement. If too dark, raise "param" a little at a time.

[Anuskuss]

Originally Posted by GeoffreyA

Not perfect but an improvement. If too dark, raise "param" a little at a time.

While I do appreciate the effort I don't think I'll ever touch the tuning parameters, as I find them too subjective. Sure I can create some beautiful colors with some fine tuning but I have no guarantee that it will look good in the next scene, let alone in a different movie. I'd rather have some "sane" defaults that some color theorist came up with or something that is based on some sort of defined standard. I mean Plex is basically doing the same thing anyway (just with an additional scale_vaapi to get the data into the right format) and while I don't think they do the best thing possible, they must've put some thought into it.

[GeoffreyA]

I agree and am of the encoding philosophy to keep the picture "as is." (Except in cases where work is needed, such as debanding anime or fixing problematic material.) What nags me is that, while there are standard ways of tone mapping, for example the ITU-R recommendations, it seems that in practice, one always has to tune the parameters a bit. I wish this were a "solved problem" but we're not there yet and subjectivity is involved.

At present, I have a project where I'm tone mapping the Lord of the Rings 4K remastering down to SDR 1080p, trying to match the remastered 1080p Extended Edition I have access to, and while I'm getting excellent results, it is challenging to match the reference exactly, and getting one scene right may fail another.

[Argaricolm]

I delete my question. To do same as MadVR does we need to do "linear" tonemapping (libplacebo has it).