PSA: AMD and NVIDIA GPUs can't do 10-bit HDR color over HDMI 2.0

German tech publication Heise confirms new AMD GPUs like the Polaris-based Radeon RX 400 lineup are incapable of delivering 10-bits per cell to generate HDR images when you have a display hooked up via the HDMI 2.0 interface instead of DisplayPort 1.2.

Rather than delivering 10bpc (1.07 billion colors), as promised in some marketing materials, AMD scales back the color depth to 8-bits per cell (16.7 million color). This is a bit of an issue considering most currently available HDR-ready displays are TVs, and those don't have DisplayPort. But it's not AMD's fault and this applies to NVIDIA too because it's due to bandwidth limitations of the HDMI 2.0 specifications.

It was already known that it would not be possible to deliver 10-bit 4K resolution at 60Hz with 4:4:4 chroma over HDMI, and AMD's own marketing material explained the cards would scale down output to 4:2:2.

The desired 10 bits per cell (1.07 billion colors) palette is available only when your HDR display runs over DisplayPort. This could be a problem, since most HDR-ready displays these days are TVs. Heise.de observes that AMD GPUs reduce output sampling from the desired Full YCrBr 4: 4: 4 color scanning to 4: 2: 2 or 4: 2: 0 (color-sub-sampling / chroma sub-sampling), when the display is connected over HDMI 2.0.

This slide from AMD was a bit misleading though:



Via: TPU