What is RGB/YCbCR?

[Jaguar007]

I recently purchased a Samsung 1400 and while setting up my Sharp Aquos TV I noticed it has a setting for HDMI that gives me 3 choices
RGB
YCbCr 4:4:4
YCBCr 4:2:2

I don't really understand the techinical info I was given when I did a search on it, I just want to know which setting I should have it on.

Thanks

[jeremy_williams]

It's how chroma and luminance are measured on the TV.

The 4:2:2 setting is the most accurate color

[JAGUAR1977]

I have the same TV, select 4:2:2 on your TV, also select YCbCR on your player.

On the HDMI setup also select Colour Matrix 'ITU709', which is the correct setting for HD, and Dynamic Range 'Normal'.

[CGYBLU]

Originally Posted by jeremy_williams

It's how chroma and luminance are measured on the TV.

The 4:2:2 setting is the most accurate color

Maybe i'm way off here, but shouldn't RGB be the best, followed by ycc 4:4:4 and last should be ycc 4:2:2

Wouldn't a link with no chroma subsampling such as RGB or ycc4:4:4 (just color conversion) be better than the 4:2:2?

Then again, I guess it all comes down to how the videos are stored at the source... DVD used 4:2:0, but I know some of the high profile AVC stuff allows 4:4:4, it's whether blu-ray actually uses this, I don't know?

[MouseRider]

Originally Posted by CGYBLU

Maybe i'm way off here, but shouldn't RGB be the best, followed by ycc 4:4:4 and last should be ycc 4:2:2

Wouldn't a link with no chroma subsampling such as RGB or ycc4:4:4 (just color conversion) be better than the 4:2:2?

Then again, I guess it all comes down to how the videos are stored at the source... DVD used 4:2:0, but I know some of the high profile AVC stuff allows 4:4:4, it's whether blu-ray actually uses this, I don't know?

If you look at it from a pure technical perspective, you are absolutely right.

RGB is "best" because it provides the unencoded color information for each pixel.

YCrCb, which is an encoded format that takes the video signal and encodes it as Luminance (Y) and two color difference signals Cb (which is blue-Y) and Cr (which is red-Y).

The numbers that follow 4:4:4 or 4:2:2 represents the number of bits used to represent each of the channels Y, Cr and Cb.

Because Cr and Cb contains difference information, it can be represented by less bits, so often it is done as 4:2:2 or and 8-bits signal.

So 4:4:4 is better as the amount of color space that can be represented is larger with a 12-bit word as compared to an 8-bit word.

The other thing to note is that RGB and YCrCb has different color spaces as well.

[welwynnick]

Originally Posted by Jaguar007

I recently purchased a Samsung 1400 and while setting up my Sharp Aquos TV I noticed it has a setting for HDMI that gives me 3 choices
RGB
YCbCr 4:4:4
YCBCr 4:2:2

I don't really understand the techinical info I was given when I did a search on it, I just want to know which setting I should have it on.

Thanks

Whichever one looks best.

It's unlikely that there will be large differences, as the conversion processes (while not foolproof) are generally fairly straightforward to implement.

Whether SD or HD, interlaced or progressive, what is stored on disc is digital component YCbCr 4:2:0 video, which takes up the least space.

The 4:2:0 means that the chroma resolution is sub-sampled to half resolution both horizontally and vertically. So for every square of four luminance (brightness) pixels / samples, each colour difference signal only has one sample. This signal is internal, and is never output by any player.

4:2:0 video is up-sampled internally by the video decoder to 4:2:2 video. This has full vertical chroma resolution, but only half the horizontal chroma resolution. So one pair of chroma samples for every two luma samples. This signal can be output over HDMI.

4:2:2 video is then up-sampled by video processing in the player or display to 4:4:4 video, where the chroma resolution is the same as luma. It's rather like scaling the chroma - there are more pixels, but there's no more information than the low-res signal.

Finally, YCbCr 4:4:4 video is then transcoded to RGB video, which is always full resolution (4:4:4). This is the final process to restore the original, native, RGB signal.

All of these processes have to be performed at some point in the replay chain before the video can be displayed. None of these signals are "better" or "worse" than any other. All of then exist at some point or another in every system. Which is best to use for HDMI connection simply depends on the difference in performance between the respective decoders and transcoders in the player and the display. And I wouldn't expect those differences to be very large at all. But by all means try them and see. It won't do any harm, and you might get a slight improvement.

regards, Nick

[Paolotto]

Thanks for the beautiful explanation welwynnick!

I have one more question: I have seen other unknown options that are about color space: for example "xvYCC".
I have a special option both on the player (PS3 calls it Super-white) and on my TV (Samsung F86 uses "xvYCC"). It seems that it is about an extended color space...
What does it mean?
Should I enable it both on the player and the TV?

Thanks for your help,
Paolo

[Getus]

That is what iám trying to figure out as wel,

apperantly xvYCC has somthing to do with "deep colour" witch provide better colour reproduction.

In order to see "deep colour" your tv must support is, your blu-ray player (ps3 supports it) and it had to be on de disk. You olso need a hdmi 1.3 cable in order to transmit it from the ps3 to your tv.

there is olso a topic that is called: playing games with RGB limited or RGB full.

I recommend reading that olso.

[MouseRider]

Originally Posted by Getus

You olso need a hdmi 1.3 cable in order to transmit it from the ps3 to your tv.

Actually, it's not called a 1.3 cable, but rather a Category 2 or High Speed HDMI cable.

It also doesn't mean that if you don't have a Category 2 HDMI cable that it won't work with Deep Color or 1080p, it might just mean it wasn't certified.

Not all cables you can buy are certified and like all other forms of certification, just because it is certified doesn't make it better than one that isn't. The certification simply provides the consumer potentially with peace of mind that it will perform as expected. You can also expect certified cables to cost more of course.

For those that are interested, you can find out about HDMI certification at www.hdmi.org.

The two levels are "Standard" or "Category 1" which are tested to perform to 75MHz and "High Speed" or "Category 2" which are tested to perform to 340MHz which is currently the highest HDMI bandwidth available.

[welwynnick]

Unfortunately even Wikipedia is confused about deep colour and colour space, so it’s no surprise even most enthusiasts are, too.

Extended colour space is referred to in many different ways: broad colour space, extended gamut, xv colour, xvYCC, IEC 61966-2-4. All of those apply – but NOT deep colour, which is something quite different. Colour space refers to the range of colours that can be represented, not the number of colours or the precision of reproduction. It’s about how deep the red can be for example, not how many million shades of red you can have.

Colour space is most easily visualised using the familiar CIE chromaticity chart, which is hopefully reproduced here. This shows how the wavelength of the light relates to the colours that we see, and how each colour is derived from the RGB component colours. The gamut (colour space) of a display is often represented with a triangular area within the chart. The SD and HD colour spaces are designated ITU-R BT.601 and 709 respectively, and these only cover about half the area of the chromaticity chart.
http://upload.wikimedia.org/wikipedi...ckianLocus.png

Xv colour covers very much more, and is intended to take advantage of the improving performance of cameras and displays, but widespread adoption is a long way off. HD-DVD and Blu-ray only use BT.709 colour space, so extended colours cannot be encoded.

I’m very fond of drawing analogies between video, and my old love, audio. Here, extended colour space is analogous to the extended bandwidth that you get from faster sampling rates (such as 96kHz instead of 44.1kHz).

Deep colour has greater depth of modulation, there are more bits per colour, so there is greater dynamic range between saturation at the top and noise/distortion at the bottom. Noise and distortion are really two different things, but I simply mean the inability of the system to maintain resolution of the smallest signals, where the colour steps are simply too big. Note that this doesn’t necessarily mean the darkest signals, though this is often where you see such limitations first. Lack of depth of modulation is first seen in large areas of gradual variation in colour and brightness, such as dark shadows or blue skies. What you see is colour banding or noise.

Digital video is generally encoded with 8 bits per colour (RGB), making 24 bits per pixel. Deep colour extends this limit with either 10, 12 or 16-bit resolution per colour. This can be encoded in either RGB or YCbCr colour space. I would say that deep colour can be considered the video equivalent of 24-bit audio (instead of 16-bit).

Having said all that, just because you see some colour banding on a display, it doesn’t mean that 8-bit video is the cause. Displays very I their ability to resolve the lower bits in a signal, probably due to poor digital video signal processing, and a good display with 8-bits may show less banding than a poor display at 12 bits.

Now, the important bit - don’t get too hung up on this. DVD, HD-DVD and Blu-ray do not, and will not, carry either deep colour or extended colour. The only sources that will support them in the foreseeable future will be a few video games and
camcorders. That doesn’t mean you shouldn’t have it, it’s just that there may not be any advantage.

Whiter than white and blacker than black are legitimate video signals, but they do not affect a properly calibrated video picture (they are like calibration setting that facilitate it) and my fingers are getting too tired….

Regards, Nick