Originally Posted by tamahome02000
Damn this stuff gets complicated. So deep color just means the color of every pixel is represented?
Nope! "Deep Color" also uses the "trick" I mentioned.
A pixel is represented by 3 "component" data values: The gray scale brightness, or luminance, denoted as "Y" and two "color difference" values that tell how to color that gray scale, denoted as "Cb" and "Cr" for blue and red respectively. The Cb and Cr values denote adding or subtracting blue and red from the gray. So for example, if you subtract all the blue and all the red from a pixel of a given, non-black luminance or "Y" value, you get a GREEN pixel of that brightness.
The simplest "data format" that works this way is called YCbCr 4:4:4. The "4:4:4" in that means what you had in mind -- i.e., there is a Y value, a Cb value, and a Cr value for each and every pixel.
What gets transmitted in broadcasts on the other hand is YCbCr 4:2:2. The "4:2:2" means that there are only half as many color samples across the line as luminance samples. Like this: Y,Cb,Y,Cr,Y,Cb,Y,Cr.... Analog color TV broadcasts do a similar trick, and have done so since the dawn of "compatible" color TV broadcasting.
When you want to record stuff on a disc however, even that's not enough! The imagery on the disc needs to be "compressed" WAY more to take up less space on the disc, and even more important to require a less demanding bit transfer rate when reading the disc. That compression is made up of two styles of things. First there is micro-compression which reduces the information content in each frame of imagery and then there is macro-compression which uses the similarities from frame to frame to reduce things even more.
The most important micro-compression is that the YCbCr 4:2:2 data is cut down even further to YCbCr 4:2:0. This is the step where the vertical color resolution is also halved. The people setting up the disc transfer may also apply softening filters that reduce detail in the imagery so that adjacent frames are more similar -- which makes the macro compression step more effective.
The result of that is sent to the macro-compression encoder: MPEG2, MPEG4, AVC, or whatever. It discovers similarities from frame to frame and encodes things by recording blocks of similar stuff plus how they move from frame to frame.
When reading the disc, the player decodes the macro-encoded stuff to get YCbCr 4:2:0 and invents the missing vertical color information to turn that into YCbCr 4:2:2. Depending on the output format you have set for the player, it may also go the extra step and invent the missing horizontal color information to turn THAT into YCbCr 4:4:4. By "invent" here, I mean the player extrapolates the "missing" color information from the "present" color information surrounding it.
OK, now one thing I haven't mentioned here is the SIZE of each of these pixel component values.
"Normal" data format for home theater stuff uses 8 bits each for Y, for Cb, and for Cr. When jiggered up to YCbCr 4:4:4 data format, that amounts to 24 bits per pixel -- 3 components per pixel of 8 bits each.
But of course the data coming off the disc is not that. It is YCbCr 4:2:0 -- and yes, with only 8 bits each per component. Since the horizontal and vertical color resolutions are both halved the "real" bit count per pixel is quite a bit less than 24 bits.
This works as well as it does because, as stated above, the human eye just can't distinguish color detail all that well, and because the brain does a fantastic job of "seeing" smoothly changing imagery from a series of pictures each of which may not be all that great looking on its own.
"Deep Color" on the other hand, means that the Y, Cb, and Cr components are processed and transmitted at MORE than 8 bits per component. Common supported values would be 10 or 12 bits per component. HDMI V1.3 allows even higher but no hardware does that yet.
If you had a YCbCr 4:4:4 data stream at 12 bits per component that would add up to 36 bits per pixel! Pretty cool, right? Until you remember that the data actually coming off the disc (be it standard DVD, HD-DVD, or Blu-Ray) is really only YCbCr 4:2:0 at 8 bits per component.
The extra bits per pixel are created by the magic of mathematics -- built around a series of assumptions as to what the result ought to look like. You could, for example, decree that nearby pixels must always represent a smooth transition of the colors between them. That means you could extrapolate from the colors you have for certain nearby pixels to the colors of the pixels in between because you know it must be a smooth transition. [If your assumptions are wrong, then of course the result will also be wrong.]
You could do this with 8 bits per component math (pretty much obsolete these days) or you could do it at higher precision with 10 or 12 (or higher) bits per component math (pretty much what all modern video processors and TVs do internally for their own, individual video processing steps).
But wait! If you want to transmit that stream to the next device in your "video chain" you are stuck! "Normal" color HDMI only lets you retain 8 bits per component. So even if you send YCbCr 4:4:4 you can only retain 24 bits per pixel!
Well the optional "Deep Color" feature in HDMI V1.3 allows you to break free of that limit. You can send 30, or 36 (or even more, although nobody does it) bits per pixel!
So this is a "good thing". But don't confuse that with seeing something that you've been missing up to now. Because the data on the disc is still YCbCr 4:2:0 at 8 bits per component.
And that's not going to change for standard DVDs or HD-DVD or Blu-Ray discs. Not ever. It is part of the disc spec. If you tried to make a disc with higher bit depth, no player would know what to do with it. At some point (think years from now) there may be a *NEW* disc format for recording Deep Color content, but that won't be Blu-Ray. It will be something else. Time to buy a new player for one thing.
There is a lot of speculation at the moment as to whether passing these extra "rounding bits" between devices will make a real, quantitative improvement in what people see on screen. It is also really REALLY hard to evaluate this stuff in real world products because each new product also comes with OTHER changes that are designed to enhance its video. So ascribing any improvement you might see entirely to Deep Color is likely incorrect.
But we are just now (this month) seeing the first devices that are trying to stake out a marketing position for this -- the Pioneer 51 and 05 Blu-Ray players -- so this forum should be full of opinions pro and con within the next few months.