Colour Sub sampling
Sub sampling: 4:4:4 / 4:2:2 / 4:2:0
In its simplest most form sub sampling is a way in which colours are illuminated in each pixel.
The definition of sub sampling and its share in producing a 4K image is subject to the frequency in which the 4K image is transmitted.
The given sub sampling and combined refresh rate is subject to HDMI various formats.
Please note that as such one sub sampling rate is not greater than another until you compare the frequency (Hz/fps) in which it is combined with.
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For instance a 4:4:4 rate as part of a 60Hz 8bits broadcast while supported by HDMI formats, is not brighter or more colourful than a 4:2:0 rate as part of a 60Hz10bit broadcast.
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This feature refers to colour sub sampling. 4:4:4 is used in content mastering, but 4K Ultra UHD is distributed via 4:2:0 standard format
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​Image courtesy of www.Audiofronitiers.com
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4:4:4 is a full bandwidth signal
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4:2:2 is displayed on 2/3rds the space
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4:2:0 is displayed on 1/2 the space
Both Blu-ray and UHD Blu-ray offer video signal stored in the 4:2:0 format.
Each pixel has a Y’ signal, odd pixel lines have no Cb or Cr and then Cb and Cr are alternated on each even pixel line.
A video content displayed on flat screen or a projector is typically subject to the following conversions:
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4:2:0 to 4:2:2
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4:2:2 to 4:4:4
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Y’CbCr to RGB
Up until now the source sent an up-sampled content in 4:2:2 format, which was routed via HDMI. The display up-sampled content to 4:4:4 and converted it to RGB. The reason for such conversion is that HDMI v1.4 and previous high speed versions did not support 4:2:0.
HDMI2.0 specifications do offer support for 4:2:0 format though only at 50/60Hz /frames per second.
Consumer UHD content is coded stored, processed and transmitted, in a colour space called Y’CbCr:
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Y’ = Luminance, or Luma, representing the brightness of the pixel
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Cb = Blue colour differences
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Cr = Red colour differences
This standard was defined back at the start of the colour TV era as a way forming colour images
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​Image courtesy of www.Audiofronitiers.com
3840 x2160
10bits
Rec. 2020
HDR
4:2:0
60Hz
70m
Guaranteed
The chart below is demonstrating the colour is noting the various colour sub sampling based on colour depth at a range of screen's refresh rates (fps/Hz)
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Chart courtesy of HDMI LLC