Originally Posted by EC1602
Guys, I have a question regarding color depth on 4K UHD Blu-ray.
I’m aware that 4K UHD Blu-rays which have HDR10 supports WCG (Wide Color Gamut) which is 10-bit color depth.
However, 4K Blu-ray titles with Dolby Vision enhancement layer is what confuses me.
They say DV supports “up to” 12-bit color depth.
From my searching, it seems that 12-bit color is used at filming/editing/mastering stage in the studio for DV.
However, it looks like they encode into 10-bit HEVC for 4K blu-rays. This part isn’t clear.
Are DV enhanced blu-ray titles encoded in 10-bit or 12-bit color depth?
It is complicated, and here is a little write-up I made for myself to reference after some research.
Dolby Vision HDR RGB Tunneling
The method Dolby Vision HDR (DV) uses to transport the signal over HDMI is referred to as “RGB Tunneling”. The 12-bit ICtCp or ITP colorspace DV signal + Metadata is encapsulated inside the regular RGB 8-bit video signal. The DV “tunneling” carries 12-bit YCbCr 4:2:2 data in an RGB 4:4:4 8-bit transport. This is possible because both signal formats have the same 8.9 Gbps data rate requirements.
DV requires dynamic luminance data which cannot be explicitly carried in an HDMI 2.0 (18 Gbps max) data stream, so it is designed to transport over HDMI 1.4 (8.9 Gbps max); at least up to [email protected]
DV base content and DV luminance (meta) data is encapsulated in an HDMI 1.4 compatible (except HDCP 2.2) RGB 4:4:4 8-bit video stream. That's why Dolby claims that DV can be sent via HDMI v 1.4, but in reality, HDMI v2.0 is needed due to the HDCP v2.2 encryption.
The DV metadata is encoded into the least significant bits of the chroma channels. Upon the HDMI EDID exchange (handshake), the sink (AVR, Display, or HDMI switch) signals the source that it supports Dolby Vision HDR "tunneling". The source then signals the sink that it's transmitting Dolby Vision HDR through an AVI Infoframe, which therefore triggers the Dolby Vision HDR mode in the sink. The display DV engine extracts the components and produces a tone mapped image.
As a result, video pass-through components must be DV 'aware' to not alter the signal, which is in effect 'hidden' inside the 8 bit RGB 'container'.
AVR’s may report DV signals in one of two ways, but both are correct:
Resolution: 4k:24Hz ->4k:24Hz
HDR: Dolby Vision
Color Space: RGB 4:4:4 -> RGB 4:4:4 -OR- YCbCr 4:2:2 -> YCbCr 4:2:2
Color Depth: 8 bits -> 8 bits -OR- 12 bits -> 12 bits