Questions on Component Video...

[Akai Rounin]

YPbPr vs YCbCr...

My Brother's 51" APEX projection television is 480 progressive, but is not HDTV and does not accept VGA input. It does have two different sets of Component video inputs. One is labeled YPbPr, the other is YCbCr... What exactly is the difference between the two, and which standard does the Xbox use? Can this video output be used for both games and DVDs? I seem to remember that for some reason the PoSPSPoo allows the component video output for one, but not the other (not sure which).

HUN-YA!

Akai Rounin

[KingJohn]

http://bmrc.berkeley.edu/frame/research/mpeg/faq/mpeggloss.html

[Akai Rounin]

Colors of Components...

Thanks, KingJohn! Actually, I found the same information through a search on Google. I guess asking for the exact difference between the two display standards was not really what I wanted to learn after all... It's been far too long since I bothered to actually study such equations with an intent to understand them. Here it is if anyone else is interested:

YCbCr
The international standard CCIR-610-1 specifies eight-bit digital coding for component video, with black at luma code 16 and white at luma code 235, and chroma in eight-bit two's complement form centred on 128 with a peak at code 224. This coding has a slightly smaller excursion for luma than for chroma: luma has 219 risers compared to 224 for Cb and Cr. The notation CbCr distinguishes this set from PbPr where the luma and chroma excursions are identical.

For Rec. 601-1 coding in eight bits per component,

Y_8b = 16 + 219 * Y Cb_8b = 128 + 112 * (0.5/0.886) * (Bgamma - Y) Cr_8b = 128 + 112 * (0.5/0.701) * (Rgamma - Y)

Some computer applications place black at luma code 0 and white at luma code 255. In this case, the scaling and offsets above can be changed accordingly, although broadcast-quality video requires the accommodation for headroom and footroom provided in the CCIR-610-1 equations.

CCIR-610-1 Rec. calls for two-to-one horizontal subsampling of Cb and Cr, to achieve 2/3 the data rate of RGB with virtually no perceptible penalty. This is denoted 4:2:2. A few digital video systems have utilized horizontal subsampling by a factor of four, denoted 4:1:1. JPEG and MPEG normally subsample Cb and Cr two-to-one horizontally and also two-to-one vertically, to get 1/2 the data rate of RGB. No standard nomenclature has been adopted to describe vertical subsampling. To get good results using subsampling you should not just drop and replicate pixels, but implement proper decimation and interpolation filters.

YCbCr coding is employed by D-1 component digital video equipment.

YPbPr
If three components are to be conveyed in three separate channels with identical unity excursions, then the Pb and Pr colour difference components are used:

Pb = (0.5/0.886) * (Bgamma - Y) Pr = (0.5/0.701) * (Rgamma - Y)

These scale factors limit the excursion of EACH colour difference component to -0.5 .. +0.5 with respect to unity Y excursion: 0.886 is just unity less the luma coefficient of blue. In the analog domain Y is usually 0 mV (black) to 700 mV (white), and Pb and Pr are usually +- 350 mV.
YPbPr is part of the CCIR Rec. 709 HDTV standard, although different luma coefficients are used, and it is denoted E'Pb and E'Pr with subscript arrangement too complicated to be written here.

YPbPr is employed by component analog video equipment such as M-II and BetaCam; Pb and Pr bandwidth is half that of luma.

This sort of makes me yearn for the good old days, when it was easy to understand why 12 bits per pixel, 4 bits per color register equalled a 4096 color pallette for the Commodore Amiga... Anyway, I posted the same question elsewhere and learned that the Xbox uses YPbPr Component connection via its optional HDTV Pack for progressive scan television sets. Too bad there is no official VGA adapter, like on my trusty Dreamcast. I guess my Brother's APEX GB5108 will have to do...

HUN-YA!

Akai Rounin

[KingJohn]

I guess they did that on purpose... Give it time, I'm sure something will be sold, especially when those things can play DivX movies, I bet we will see a lot more come out, before we see a DivX DVD again.