12G Video Assist HDR Limited Contrast

Hi All:

Looking for some clarity on black/white levels on the 12G Video Assist HDR. Here are the details:

Windows 10 Resolve Studio 17.4.6->Thunderbolt
Ultrastudio 4k Mini Desktop Video 12.4->SDI
12G Video Assist HDR Firmware 3.7

Signal Chain:

Toolbox->Generators
10 Step Contrast
BT.2111 Color Bar HLG Narrow

Resolve set for Rec.2020 (Rec.2100 HLG) timeline, HDR 1000 timeline luminance, Rec.2020 (Rec.2100 HLG) output color space. DRTs are both DaVinci, Graphics White Level is 200 nits, White Point Adaptation is enabled, HDR mastering is 1000 nits. HDR10+ Metadata is on.

Under video monitoring, UHD 2160p 29.97 is selected, SDI configuration is set for single link, data levels are video (YCbCr), with sub-black and super-white data retained.

Video bit depth is 10 bit with bilinear monitor scaling and HDR metadata is enalbed over HDMI.

I've confirmed these settings look good in the UltraStudio 4k Mini SDI Output Settings. The only additional info is that the 3G-SDI is set to SMPTE Level A (there is no difference made when it's toggled from Level A to Level B)

The two generated test patterns are missing the lowest gradation of black and all of my video looks like the blacks are being crushed similar to a YCbCr/RGB (limited/full) mismatch. This is not the case.

I've messed with the brightness and contrast on the 12G HDR, my current settings are 50% contrast, 80% brightness and 30% saturation.

I've confirmed that I can see the entire range on an LG C1 that is currently connected to the HDMI output of the UltraStudio.

It seems like the contrast control isn't centered on the 12G Video Assist, either the whites clip out or the blacks clip out.

At 100% contrast the lowest black level is visible, but the white levels above step 6 are clipped. The lowest black level disappears on contrast levels below 64%, but at 64% the top three white levels are clipped.

The highest white level only returns at contrast values of 54% or lower.

All of this differentiation remains across the entire brightness range.

I have no usable settings where I can see the entire range.

What's going on with this device? Is this a workflow issue (as potentially indicated by tech support)?

Thanks in advance for any advice.

Hi, seeing similar issues here with the same(ish) hardware setup - I'm using SDI instead of HDMI as I couldn't find an HDMI cable.

What do your scopes say, both on the Video Assist and in Resolve?

Inside Resolve, the 10 step pattern clips out on the high end (step 8 is truncated 1/2 step above 7 at 1000 nits), but steps 1-7 are clearly visible. There appears to be a scaling issue with the generator in HDR mode, and it's trying to land step 10 at 10k nits even if HDR mastering is set to 1000 nits. Curiously if you change the HDR mastering levels in project settings, the clip stays at the same place - 1000 nits.

Bypassing color management on the 10-step (right click in the timeline) stops the clipping at 1000nits, and both in Resolve and the Video Assist now show a full 10 steps in the waveform all the way up at 10k nits. Additionally, the video assist now renders the 10th step, but no way is it at 10k nits output so there's a scaling issue here. The metadata still says ST2084 (1000) so there is something funky going on if it is able to render the 10th step and not clip at 2500nits or whatever the native capability is. Notably my MBP display is also HDR capable and is rendering the top few steps >white, but the image does still clip at the same place regardless of whether "Bypass Color Management" is set or not.

All of the above has to do with the top end. The Video Assist appear incapable of rendering the bottom 3 steps, which it should have plenty of information for. There is no evidence in the waveforms on either Resolve or the Video Assist that the bottom end is clipping, it just won't draw them. Changing the display brightness on the Video Assist doesn't seem to affect the visibility of any of the bars, so it seems like they're getting clipped prior to the brightness control.

The BT2111 Color Bars (either Full or Narrow) do not agree in the waveforms between Resolve and the Video Assist, so not sure what is going on there.

I have not yet had a chance to validate with an additional display downstream of the Video Assist, will get to that tomorrow.