Originally Posted by 8mile13
Whatever it is there is no increased bit depth when set to Wide Color.
There is no/minimal CMS being used when wide color is selected, the panel is just running at its native gamut.
To constrain the gamut to spec, you are effectively throwing away bits to implement the CMS.
So if you disable the CMS, you have better gradation (reduced banding) but less accurate color.
Here is the simplest way I can explain it:
To be clear about what this image is showing: the outer "triangle" that is colored in, covers the entire gamut that the human eye can see. The dotted triangle is the BT.2020 spec (UHDTV) and the solid inner triangle is the BT.709 spec. (HDTV) That doesn't actually matter, but it saves me having to explain it.
I have added a white line for illustrative purposes. This image is only a 2D representation of color, but the reality is that it is three dimensional. That doesn't matter so much for this explanation either.
And as note of caution, I am using the terms gradation, precision and bit-depth interchangeably.
If we are working in 8-bit RGB we have signals that can range from 0 to 255 for each red, green, and blue component.
If you were to send a 000,000,000 signal, it would be in the center of the triangle.
If you were to send it 000,255,000 that is 100% green, and would be right at the very green corner of the triangle.
If you were to send it 000,128,000 that is 50% green and it would be halfway between the center and the corner.
Now to keep things simple, imagine that you have a panel that is capable of 12-bit gradation, with a native gamut that covers the BT.2020 gamut exactly - the dotted triangle in this illustration.
But you are not watching Ultra HD content on it, you are watching regular HD (BT.709) content on it - the smaller solid triangle in the middle.
Now look at where the inner triangle intersects with that white line - it's roughly 1/3 of the way along it. By having a very wide native gamut, and using a CMS to bring it to spec, you have effectively turned a 12-bit panel into a 4-bit one along that axis.
If you look at 100% green for the BT.709 triangle (the corner) it's closer to halfway along the line, so you have the equivalent of maybe a 6-bit panel there.
Red and blue are a lot closer, so you won't lose so much precision from constraining the gamut with them - though this is a CIE xy chart rather than a CIE uv chart, so the difference is actually bigger than it appears here.(Technical note: a 12-bit panel would actually have 4096 shades of gradation, and 1/3 of that would be 1365, which is actually still more than 10-bit (1024) but hopefully you see the point I am trying to make - you're losing a lot of precision)
Now today's displays are a lot closer to the BT.709 spec than that, but the best we have on the consumer side is only a 10-bit panel with the best LCDs and SXRD displays. Depending on how you want to count it, technically you could say that a Plasma has more gradation than that (just look at Panasonic's numbers - 10-bit only has 1024 steps of gradation but Panasonic advertise thousands) though in reality, I would argue that a Plasma typically shows less than 8-bit - and that is at its native gamut. Once you start using a CMS to reduce the gamut further, you are losing even more precision.
This is why it's actually bad
for displays to have wide native gamuts - at least when they are intended for displaying BT.709 content. Once you go beyond the BT.709 gamut, you need more and more precision to make up for what you have to throw away to bring the panel back into spec.
That's why, as long as it can cover the BT.709 gamut in its entirety, LCDs using white LEDs in their backlight, rather than RGB LEDs can actually put out a better picture. White LED backlit sets have a native gamut that is very close to BT.709 and don't need much correction, so they should have very good gradation. RGB LEDs cover an extremely wide gamut, so you are losing a lot of precision to bring them into spec and potentially a 10-bit RGB LED backlit display could have worse gradation than an 8-bit White LED backlit display.
It's also why a 10-bit OLED set with its very
wide gamut can still show banding when displaying BT.709 content.