In 4:2:2 color sampling, how much of green is sampled?

[Luba C]

In 4:2:2, the first digit means Y' (luma) is fully sampled, the second digit Cb' means that Blue minus out the luma is sampled at 50%, and the third digit represents Cr' (red minus out the luma) is also sampled at 50%, is that correct?

What about green, there's no mention of green in 4:2:2, how much of green is sampled?

Finally, if most of the color is green, followed by red, and the least is blue, then why sample more green versus red, and more red versus blue?

In 4:4:4, luma, blue, and red are completely sampled, but again there's no mention of green. I assume green would also be fully sampled??

Thanks for clearing up this mystery for me.

 

[Graeme Nattress]

YCbCr attempts to de-correlate luma from chroma, as we're more visually sensitive to luma resolution and it allows easier removal of visual redundancy from the three RGB channels.

What that means is that any brightness change is fully sampled, but the chroma is sub-sampled by the indicated factor. R, G and B are reconstructed back from the chroma and luma. Green is makes up a lot of luma so it's sampling is effectively that of luma, whereas pure red or blue will be sampled at the reduced rate. Colours in-between will have effective sample rates in-between those extremes.

Graeme

 

[Andrew M.]

Is it true that monitor with YCbCr input of 1.5GHz shows better color fidelity of 1080p video feed that the one with HDMI interface?

I am thinking to start converting to some digital feeds for large monitors here.

 

[Luba C]

I think I read the green makes up 67% of luma, so it is correct to think that green is being sampled at 67%? Or it is more accurate to think that green is sampled at 100%, just like the luma is being sampled at 100%?

And since pure blue and pure red make up a small portion of luma, they are separated out, and sampled at 50% in 4:2:2?

YCbCr attempts to de-correlate luma from chroma, as we're more visually sensitive to luma resolution and it allows easier removal of visual redundancy from the three RGB channels.

What that means is that any brightness change is fully sampled, but the chroma is sub-sampled by the indicated factor. R, G and B are reconstructed back from the chroma and luma. Green is makes up a lot of luma so it's sampling is effectively that of luma, whereas pure red or blue will be sampled at the reduced rate. Colours in-between will have effective sample rates in-between those extremes.

Graeme

 

[Graeme Nattress]

REC709 luma coeficients are: 0.212671, 0.715160, 0.072169.

Green alway looks like it's fully sampled - I don't think you can just say it's 71% luma so rest must be chroma and say 71% at 100% + 29% at 50%

Graeme

 

[Stacey Spears]

Is it true that monitor with YCbCr input of 1.5GHz shows better color fidelity of 1080p video feed that the one with HDMI interface?

No. As a side note you can send Y'CbCr 4:2:2, 4:4:4, or R'G'B' over HDMI in 8, 10, or 12-bit. One is not automatically better than another for various reasons. Some displays, for example, convert everything into 4:2:2 for processing. The Panasonic VT20/25 does this. In fact, if you send in anything other than 4:2:2, you end up with a slight YC delay.

I published an article almost a year ago discussing this in the context of Blu-ray.

 

[Andrew M.]

Stacy, very god article, thank you.
I like the test procedures you are proposing.

I see the analog world even for video is slowly going away.
Even reference monitors for video material have to be scrapped.
I have to get up to date with monitor calibration for RED digital camera and the best color space to use.

I think good 50” + monitor 4:4:4 10 or 12 bit with 120fps will be the standard for the near future.

Though I will wait for 4K monitors before the upgrade.
I presume 4:4:4 monitors can accept any color space, correct?

But what if I load the LUT and calibrate the monitor, will I restrict the color space it can handle?