Isn't the CIE color space is a 3D model?  I've seen it in layers before.  I always assumed the standard 2D pic is at the HSB equivalent of the "brightest" slice (desaturating toward the middle where the colors add).

 

If this is true, I cannot find any pictures of what 709 and 2020 look like (using all 3 axes.)

 

Shouldn't that be part of the spec, or am I misunderstanding something?

this?

Here's a video of all the valid YCbCr codewords in BT.709.

http://www.w6rz.net/overscancrop.zip

Ron

 

I've done several such google image searches.  Which one were you thinking showed the full 709?

Can we get rec. 2020 with the current hdmi? Or is that why we need the new standard?

A color space is defined using the color coordinates and the white point. A 3D chart is a nice way to show that information but it isn't needed.

No current video connection supports the Rec. 2020 color space and hopefully HDMI 2.0 will support it.

You don't need a new connection for BT.2020 color.
Only for 4K at higher framerates and bit-depths.

If the current hdmi can do rec. 2020 color, I wonder why there haven't been much comparison between 709 and 2020

There's no BT.2020 content.

Ok, my thinking was off

HDMI can only signal a color space that is listed in the HDMI specification which is why the press release for HDMI 1.3 mentions the addition of the xvYCC color space. The Rec. 2020 color space was only defined last year so the current version of HDMI does not support it.

xvYCC was different because it operates using the 0-16 and 235-255 range which was previously off-limits for video content.
I don't think there is anything "special" about BT.2020, and it's just a standard colorspace like BT.709, sRGB, Adobe RGB etc.

I just read its supposed to be better color. I assumed BT.709 is not good enough for 4K

The sRGB color space supports full range video and has been supported by HDMI since the first version. And limited range video allows for video to be in the range of 1 to 254 (only 0 and 255 are not allowed). That is how calibration discs allow you to calibrate your display with images that are below black or above white. Also here is a link to an explanation of how xvYCC works and the article mentions that it only uses the video range of 1 to 254.

If a color space isn't supported by the HDMI specification than HDMI can't send it. That is why the xvYCC color space had to be added with HDMI 1.3 and why the Rec. 2020 color space will need to be added.

You can send any color space you like over HDMI. xvYCC is not handled the same way as normal color spaces because it uses the below-black and above-white ranges.

Color is essentially sent as percentages. So if you send "100% red" that does not actually define a specific color.
The device on the receiving end can map this "100% red" input to whatever colorspace it likes. Right now, displays only understand BT.709.

If you send BT.2020 content to a display that only "understands" BT.709, it will just look very desaturated, because the values are intended to be viewed on a display with a much wider gamut.

The HDMI website put versions 1.0 to 1.3 of the HDMI specification on their website and I am just telling you what I have read.

The only way that you can send 100% of a color is if that color is defined, color spaces are used to define those colors, most color spaces don't use monochromatic colors, even when a color space uses monochromatic colors there are many possible colors that can be chosen, almost all HDTVs understand both the Rec. 709 and Rec. 601 color spaces, and many professional displays support larger color spaces such as the Adobe RGB color space or the DCI P3 color space. I would recommend reading up on this subject. The cheap way would be Google and Wikipedia though if you are really interested I would recommend the book "Digital Video and HD" by Charles Poynton.

I use computers every day that are calibrated to custom color spaces over HDMI. (because I need to go beyond BT.709/sRGB for photo editing, and no display matches up to the "standard" color spaces perfectly)
As I said, HDMI is basically just transmitting colors as percentages.

It may be "flagged" as BT.709 (I'm not even sure that it is) but you can send any colorspace you like over HDMI as long as the device on the receiving end can be set to display it correctly.
If you send Adobe RGB values over HDMI to a display with an Adobe RGB gamut, everything displays correctly.
If you send Adobe RGB over HDMI to a display set up for BT.709, the image will look desaturated, because it's just displaying RGB percentages, but assigning them to the wrong colorspace.

HDMI supports several color spaces and you might just be using one of the larger color spaces. A computer can be set to use only a portion of a color space but that doesn't have anything to do with HDMI.

It would do much more than that since it would shift any of the colors that include green (which has a different color coordinate in the Adobe RGB color space). Even with a color space that only uses monochromatic primary colors you still have to pick the frequency of a color and for example there is a very noticeable difference between 610nm red and 630nm red. Both are red but they are not the same frequency of red. For displays to maintain color accuracy the primary colors must be mathmatically defined.

The output device knows that it is outputting BT.2020 color, or whatever other colorspace it needs to, and adjusts the values it is sending to the display accordingly.

100% red, 50% green, 20% blue is a different color depending on the colorspace it's assigned to.

In the case of computer calibration, measurements are taken of the display with a meter, and a custom profile is created based on those measurements, so the computer knows exactly how much of each color component to send to the display, to display accurate color.

Any values a player supporting BT.2020 will output, will be specific to the BT.2020 space, rather than being custom tailored to your display, just like any player today outputs values assuming they are being displayed in the BT.709 colorspace, and applies the transformations required to convert BT.601 to BT.709 in the case of upscaling DVD players.


If you play a Blu-ray (BT.709) on an upscaling 4K player which is outputting BT.2020 color to the display, it would for example transform "100% red in BT.709" to a value of 50% red - assuming that BT.709 red is only 50% as saturated as BT.2020 red; I don't know the real value off the top of my head.

It is very likely that all 4K UHDTVs will be capable of accepting the Rec. 709 color space for 4K resolutions. The only reason that Rec. 601 to Rec. 709 conversion was needed with HDTV was because analog video connections were used. There is no need to do that with digital video connections (DVI, DisplayPort, and HDMI) since they send the color space information with the video signal.

This is done because it is assumed that an HD signal is going to be using the BT.709 colorspace. Because the player is upscaling from SD to HD, and outputting an HD signal, it also has to perform colorspace transformations to convert from BT.601 to BT.709.

The same situation is likely with 4K players and displays. (though not the first displays, because none of them support BT.2020 yet)
They will be assuming a 4K signal is BT.2020, so the player will have to convert BT.709 to BT.2020 when upscaling HD to 4K. (or BT.601 to BT.2020 when scaling SD to 4K)