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SvennoJ on 05 October 2017
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Peh said:
SvennoJ said:

4K at 60hz 10 bit is 'only' 13.9 Gbps, within the max 14.4 Gbps max video bandwidth of an 18 Gbps cable. 3840x2160x60x30 / (1024x1024x1024)
I can't find any hard info on actual support though, nor do my tv or the ps4 pro offer any info on the bit depth, color space used or chroma compression. Just 2160p RGB all frequencies upto 60hz supported with HDR. I guess I'll need to find/make some test patterns to check for chroma subsampling and bit gradients.

HZD looks great though, but with nothing to compare, who knows what I'm looking at.

I've found a site which does the calculation and explanation, bit it is in german.

 

https://www.professional-system.de/thema/4k/

 

For 8bit 60hz he calculates 16.7gbps

and for 10 bit 60hz it is 20.4 gbps. This exceeds the 18 gbps for the hdmi 2.0 port.

 

On different forums they also conclude the same, that it can't run on 10 bit 4k 60hz and chroma 4:4:4. This also explains why I cannot choose this setting on my PC.

 

Well at least it passes the 4:4:4 test http://vah.dy.fi/testcard/3840x2160.png
No chroma subsampling anomalies at 2160p60 mode with that test image.

Yet the bit depth isn't that easy to test as I have no picture editor that supports 10 bit files. No way to check if it's actually 10 bit to start with. This image looks absolutely smooth via ps4 pro on my tv http://www.abload.de/img/16-bitetck4.png, looks dithered in my browser on my laptop.

Then ofcourse what happens when HDR switches on. HDR is basically just meta data, same 10 bits is used regardless, so it shouldn't have any effect on the actual bandwidth.


Not sure how that site calculates it as 3840x2160x60x24 / (1024x1024x1024) is 11.1 Gbps, not 16.7 Gbps
They start with a massive overhead of 4.176 × 2.222 per frame to get to 16.7 Gbps for 8 bit 4:4:4 60hz, yet 4:4:4 works at 2160p 60hz I just confirmed, while 16.7 Gbps exceeds the 14.4 Gbps max video bandwidth (sound needs to go through that 18 Gbps as well) That site must be wrong?

Anyway the official site says only 4:2:0 is supported for 10 bit 4K 60hz
https://www.hdmi.org/manufacturer/hdmi_2_0/hdmi_2_0_faq.aspx#146

So yeah I guess it must use chroma subsampling at 10 bit. So basically you can choose between 4x the color depth for 1/4 of the pixels (4:2:0), or stick to 8 bit and have color info for every pixel :/ I guess 10 bit 4:2:0 makes more sense with checkerboard rendering.