HDR to SDR and 2020 to 709 on Vero4k

Help and Support Vero 4K / Vero 4K +
1

I’m wondering if there is any control (even if via command line only) over HDR processing (tone mapping) and color space conversion on the Vero4k?

My setup is perhaps “a little” odd, I have a projector which is kinda-sorta capable of UHD and a wide color gamut (more than rec 709) but has no HDR support. I use a HDfury Linker to convert the HDMI/HDCP 2 signal from my UHD bluray player to HDMI/HDCP 1.4 and also provide a custom EDID that specifies support for the rec.2020 color space but not HDR. This works quite well, the player outputs the correct colors and does the HDR to SDR conversion for me (with controls available to tweak the brightness etc).

I am now trying to get the same tricks working for the Vero, but I have two problems:

  1. Although my Linker claims to receive a rec 2020 signal from the Vero, the colors are very over-saturated unless I use a rec 709 setting on the projector. I conclude that the Vero is outputting rec 709 values.
  2. The overall brightness is lower than from my bluray player, and I have not found any adjustment for this.

I assume this processing is done entirely in the SoC hardware and is a black box with limited control?

2

Hello,

It sounds more like your display not handling dithering from Rec 2020 → Rec709 properly. I understand that projector implementations of 4K are quite new and I don’t believe there are any projectors yet on the market that can take Rec2020 signal and output as such. Instead, there seems to be some internal conversion.

root@osmc:/sys/class# find /sys/class | grep brightness
/sys/class/video/brightness
/sys/class/video/vpp_brightness
/sys/class/amvecm/brightness
/sys/class/amvecm/brightness1
/sys/class/amvecm/brightness2

There are sysfs parameters, but no GUI based control for this.

You should be able to toggle HDR output during playback with:

echo 1 > /sys/module/am_vecm/parameters/sdr_mode

It should also be possible to force an EDID to change the display’s supported parameters. This is a more unique use case; but I can appreciate the potential for allowing EDID overrides beyond what we currently support. Currently we allow for changing supported video modes to be changed trivially.

Sam

3

HDR/rec2020 to SDR/rec2020 is definitely not working right with the vero.

This is from my bluray player, with the projector set to rec2020:

D75_1740_ub700_sdr_2020
D75_1740_ub700_sdr_20202048×1369 931 KB

The same file (which is HDR and rec2020 format), on the vero;

D75_1737_revo_sdr_2020
D75_1737_revo_sdr_20202048×1369 1.01 MB

And the same, but with the projector switched to rec709:

D75_1738_revo_sdr_709
D75_1738_revo_sdr_7092048×1369 963 KB

On the other hand, if I change my EDID to allow HDR output both devices produce identical colors (but the “gamma” is all wrong because the projector doesn’t understand HDR and doesn’t have a PQ tone curve. I will probably try creating a custom curve rather than rely on the SDR conversion at the source device, but thanks for the pointers anyway.

4

Adjusting /sys/class/amhdmitx/amhdmitx0/attr might give some clues.

5

@sam_nazarko

What does/should happen with the Vero 4k if you are watching BT2020/HDR 4k on a non 4k system?
My setup is Vero4k -> Marantz HDMI 2.0/2.2 4k ready AVR -> Panasonic HDMI 1.4 1080p plasma.

4k HVEC bluray rips look superior to me but I assume it’s the higher bitrate/superior encoding over H264 as I’m not getting the benefit of wide colour gamut or HDR.

I’m not having any problems - Just interested.

By the way - I’ve been a XBMC/Kodi user back since the hacked xbox days and used pretty much everything from a Shield TV to a custom built PC. For ease of use, ease of maintenance, reliability and picture quality the Vero 4k beats them all!

1 Like
6

You have colour space dithering and HDR to SDR conversion kicking in

Sam

7

Thanks for the info.

Is that done is software or hardware?

8

Hardware: as the very signal sent out differs.
This is controlled by the hdmitx module