Graphics Cards

[offler]

Hi.

I paired my Radeon VII with LG 27GN950B display, which has 4k resolution and up to 144Hz refresh rate and  HDR10 color depth.

For the convenience here are technical details of both:
https://www.amd.com/en/products/graphics/amd-radeon-vii
https://www.lg.com/us/monitors/lg-27gn950-b-gaming-monitor

The problem lies with the Display Port 1.4 specification and DSC feature - which is a compression.

The display allows in its OSD to switch between DP 1.2, DP 1.4 and DP 1.4 (DSC).

Each of the settings allows different bandwidth and thus resolution/refresh rate/color depth, while DP 1.2 would be most limited.

DP 1.4 allows 4k resolution on 120Hz and 8bit color depth (sRGB).

DP 1.4 (DSC) should allow 4k resolution on 144Hz and 10bit color depth, however display downclocks to 95Hz..

I know, the problem might be with cables, but atm i am using "Vention DisplayPort (DP) 1.4 Cable 8K 1,5 m Black", while i also tested the display/card with cable which was bundled with the display and both seems to work in exactly same way.

Good news for me is that i want to use the display mainly on following modes:
3840x2160 @ 120Hz 8-bit sRGB - for gaming and viewing photos
3840x2160 @ 60Hz 10-bit HDR/WCG - For UHD
3840x2160 @120Hz 10-bit calibrated WCG for photo editing

Even when i WANT to avoid DSC (as its not a lossless compression) i would like to ask what can cause that display/card are not working up to the specs, even when driver indicates 8,1x4 Gbps.

[elstaci]

Read this previous Thread where a User was also asking about DSC but on his professional GPU card and AMD Expert on Professional GPU card replies: https://community.amd.com/t5/drivers-software/w5700-dsc-support/m-p/453422#M139762

@fsadoughmight be able to answer your question since the Radeon VII consumer card uses Professional GPU drivers and is similar to the Radeon VII PRO professional GPU card.

[offler]

Thx for the links, however it seems that the situation is very different from mine.

I have directly connected Radeon VII to the display. No hubs...

[elstaci]

I realized that but I mentioned it because is involves DSC and I was hoping some of FSADOUGH's answer might have been useful to you.

[fsadough · Accepted solution]

We have started supporting DSC with our NAVI boards. Radeon VII is a VEGA board.

[offler]

Thanks, that explains it.

Just out of curiosity HDR10 media profile is obviously supported, what about Forward Error Correction?

[fsadough]

This is a consumer product you have. The pro version supports HDR10 and the consumer version should do as well. In terms of FEC, I am not sure, if this applies to GPU at all. FEC is for data transmission. IN GPU technology we talk about ECC (Error Correction Code) and the Pro version of Radeon VII does support it. You can check in Radeon Settings if the option ECC is available.

[offler]

I proceeded to test both Radeon VII and the display with UHD content in Windows. Unfortunately i ran into a different issue, which i am going to consult with LG support.

Compatible bluray optical drive should arrive by Sunday, so far I am testing demo videos.

GPU/ Displayport Settings:
4k at 60Hz at 10bit RGB 4:4:4 PC standard
HDCP 2.2 Enabled

VLC Player:
Its configured to Direct3d11 video output. Using any other renderer results in SDR content.

Windows setting
HDR: ON
The display automatically switches into "Vesa Certified HDR Mode" (HDR600). Any color calibration becomes unavailable, and the display announces this mode by HDR icon in upper right corner.

When tested video is opened in Window, colors look OK (richer and bit oversaturated as its typical for those demo videos).

When i enter fullscreen mode, display switches to bit different HDR mode. OSD allows to alter "Variable Backlight" setting which  is not available in any other mode.

The issue now  is, that image is very dark.

Windows setting:
HDR: Off

Windowed video starts in SDR mode, but once setting fullscreen, and cursor and all controls disappear, display enters the HDR mode and colors are displayed properly, and "Variable Backlight" is not available as a setting in display OSD

Unfortunately VLC does not work properly with BluRays and UHD Blurays.

Cyberlink Power DVD20 ultra
When opening any UHD content, software asks to turn on HDR mode in windows. If On, behavior is same as with VLC - Windowed mode has correct colors, fullscreen goes very dark.

If Off content is displayed in SDR mode.

Windows media player:
Its capable to display the content only in SDR mode and output colors are used a baseline to tell the different.


I suspect that the UHD issue is on monitor side (yes i tested 3 different cables) and the variable backlight does not work at all, and i am already asking LG support about it.

If there is anything which could be related to GPU, please let me know.

Edit:

The issue has been found, its in Windows itself.

Settings>Display>Windows HD Color Settings>Enable HDR

Then there is a slider at the bottom. If its set to 0, every HDR video content has correct brightness, however brightness of Desktop and the other content is dark. Those two values are in some way inverted.

In some situations, when HDR video is started in fullscreen the brightness may be displayed correctly, but its limited to specific videos.

[fsadough]

Feel free to file a support ticket, if you think this is related to GPU. I am not dealing with consumer products.

[offler]

I managed to overcome this issue.

combination of Media Player Classic and madVR renderer allowed me to enable HDR and pass the HDR Metadata to the display, BUT...

- Refresh rate has to be on 95Hz or less. Then and only then 10bit colors will be available.
- System should NOT use a custom display mode. It will force 8bit colors.

Renderer itself will use "AMD GPU" mode instead of "OS HDR" mode and the brightness will be correct.

Also to confirm that the colors are OK, i viewed Blade Runner (final cut) on three different media - DVD, Bluray and UHD Bluray. Colors visually matched.

Also on custom resolution... Using it for getting custom refresh rate (matching the movie) is good for overall experience. However Custom resolution and 10bit colors dont work together.