Why Chroma 4:2:0 only for certain video output formats ?

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Why Chroma 4:2:0 only for certain video output formats ?

The Chroma selection is visible only when one of the 4K output formats is selected. Why is not available for 1080p formats ?

Even within 4K , its usually locked to 4:4:4. The 4:2:0 option shows only for certain 4K formats like only for 50hz and 60hz but not for 30hz or 24hz. What is the reason for this ?

Why can't the user have to option to select 4:2:0 regardless of what the output format is ? After all its the standard chroma format for any video (sd, hd, 4k).

Apple TV 4K, tvOS 16

Posted on Jan 13, 2023 12:50 PM

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Answer 1

Urquhart1244

Level 10

146,232 points

Jan 14, 2023 12:03 AM in response to p_f_m

HDMI standards pose additional restrictions to valid chroma settings for the HDMI signal. Verify if that applies to your setup.

HDMI 1.4 or lower requires 4:4:4 or 4:2:2 chroma. 4:2:0 sources will be converted (lossless) by the HDMI sending device.
HDMI 2.0 or later can use 4:4:4 or 4:2:2 or 4:2:0 chroma.

If one of the HDMI devices or cables matches HDMI 1.x, then the HDMI handshake will cause HDMI 2.0 devices to use the HDMI 1.x standard. For 1080p SDR, it really doesn’t matter which chroma setting is used, as the HDMI bandwidth will be under the lowest HDMI specification anyway; 4:4:4 doesn’t cause any limitations in that case.

HDMI version comparison - HDMI - Wikipedia

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Answer 2

p_f_m Author

Level 1

8 points

Jan 14, 2023 9:04 AM in response to Urquhart1244

so if all devices and cables support HDMI 2.0 then 4:2:0 option should be available in all formats ? If compatibility is the issue then I suppose it wouldn't work for any output format, but its at least allowing to select 4:2:0 for, interestingly, higher refresh rates (50hz+) but not for lower. I know the TV supports HDMI 2.0 and I think I have a HDMI 2.0 cable connecting it to the tv as well.

Using 4:2:0 allows for flexibility in external video processing like letting the TV or an external video processor do all the chroma upsampling to rgb, not too concerned about bandwidth limitation, so I am expecting to use it for 1080p as well. That way I can have all the video processing heavy lifting done by the TV or perhaps a AVR or video processor of my choice.

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Why Chroma 4:2:0 only for certain video output formats ?

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