HDR to SDR conversion: V vs 4K+

While I’ve been pleased with the V in some respects, one thing I’ve been disappointed by is its HDR to SDR conversion. I’d understood that the V might actually be better than the 4K+ in that regard, but I’m finding the output from the V to be far too dark. The display I’m using for testing HDR to SDR conversion is an old Panny plasma, and the 4K+ is doing a much better job. I just compared with both on December OSMC, same settings throughout Kodi, and I don’t find the V’s output to be watchable, it’s so dark. For example, in Back to the Future 3, when Marty is chased from the saloon bar through the town, the sequence is shot in brilliant sunshine. Played on the V, HDR to SDR almost makes the sequence look like it was shot on an overcast day. With the 4K+, the bright sunshine is present and correct.

Is this something that others have picked up when comparing SDR conversion across the devices?


The first thing I’d check is if your settings are the same on your Vero 4K + and Vero V as that can make a significant difference.

There are different tonemapping algorithms on Vero V and we also have a separate presentation layer for video vs UI.

I’m sure with some screenshots of what’s expected vs what you see we will be able to make further improvements.


Thanks for the reply. I’ve checked that the 4K+ and the V are on the same settings, both have max display luminance set to 100 and I’m switching the HDMI lead from one Vero to the other to ensure there’s no confounding with the input to the TV. I’ve struggled to get useful screenshots for a couple of reasons: it seems Kodi still doesn’t support screenshots for HDR sources even if they are being output in SDR; and because the display is a plasma, my camera is struggling to get a useful shot (whereas it can with an OLED).

What I would say with the V is that the underlying colour profile of the SDR conversion is actually very good, it’s just that the brightness is too low . If that could be fixed I suspect the SDR conversion would be better than the 4K+. I’ve tried different values for max display luminance but have not been able to achieve a satisfactory result.

Can you get a better picture by adjusting contrast or brightness?

Playing with the Kodi in-play brightness and contrast controls turned out to reveal a possible HDR10+ bug with the V.

I first went to Back to the Future 3, and was puzzled to find that the contrast/brightness controls had no effect on the picture. I tried a couple more titles, and they worked. Rebooted, and BTTF 3 again had no-effect from the contrast/brightness controls. So I thought, what is different about my mkv of BTTF 3? And then I realised: it’s HDR10+. So I went to the small number of other HDR10+ titles that I have (Hot Fuzz, Shaun of the Dead, The Shining), and in all cases, the contrast/brightness controls do not work.

I switched over to the 4K+ and the contrast/brightness controls work just fine when playing HDR10+ via SDR conversion, so this is an issue with the V.

No idea if helpful, here is a log of in-play attempts to adjust contrast/brightness on an HDR10+ file played to an SDR display.


And to answer the previous question, on my regular HDR10 titles I’d say that pushing the contrast up to the high 50s gives a much better result, but appreciate there is an element of subjectivity here!

Thanks for testing and pointing up the HDR10+ issue. We’ll look into that.

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Upon further investigation, it appears to me that the “Display maximum luminance” GUI setting is having no effect on the V, whereas it has a clear effect on the 4K. When comparing the V and the 4K into the same old plasma, changing the max luminance setting on the 4K has an obvious effect when playing HDR10 content (eg max luminance=50 has a lot of contrast, whereas 350 is very dark). With the V, I’m not seeing any difference at all regardless of where I set the max luminance value, everything is just dark.

For now I have a workaround, i.e. I just use the 4K for now (max luminance=75 is pretty good for the TV in question), but sharing this in case it provides a potential lead as to why I’m finding the V is so much darker when converting HDR.

I’ve been aware that doesn’t work. We left tonemapping on the V the way AML coded it - they have some automatic dynamic tonemapping for HDR10 material which we didn’t want to mess with. TBH I was waiting for customer feedback - now I’ve got it, thanks!

We’ve implemented brightness and contrast for HDR10+ and HLG when converting to SDR now. It will be in the next update, or you could test it from staging right now.

perhaps the automatic tonemapping is fine for a relatively bright LCD, but the plasma I still have running is rather old and not bright at all, so that’s where the user adjustment comes in handy. I’ve looked at replacing the TV but it does the job fine for the type of use it gets.

Try this:

echo 50 | sudo tee /sys/module/am_vecm/parameters/panell

If it works, we’ll get that setting brought out to Kodi.

thanks for the suggestion, but no difference that I could see, regardless of which value I use in the command. Still get the same, very flat image. Happy to post a log if that helps.

No need. Here on my Panasonic LED if I send 50 and 400 (the default) alternately while watching a HDR10 movie I can easily see a difference though it’s not huge.

on the V4K, I find the difference between max luminance=50 vs 350 to be quite dramatic. I can try this with a terminal open in the same room as the TV, but the level of adjustment that I need on the V is quite large, and even at the low end of the range I’m nowhere near the contrast I get from the V4K at max lum=75.

OK, well what AML actually do with that value is buried in the code somewhere. One day I’ll investigate further.

thanks for trying, looks like I might have a spare V for a little while.