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RGB vs. YPrPb
Excellent tip from Allan Joyner, Jr:
"You can vaguely think of Y,Pb,Pr as RWB (W for white) when comparing with RGB. In
reality all three subsignals are different (contain different proportions of red, green,
and blue; the R of RGB is 1.0R + 0.0G + 0.0B).
The "white" (Y, luminance) carries full horizontal resolution while the Pb
and Pr carry half. Whereas for RGB all three lines must carry full resolution.
An RGB cable set may look the same as a Y,Pb,Pr cable set although the plugs and jacks
may differ. The RGB cable needs more quality overall, specifically all three lines need to
have the full bandwidth that only the Y line of a Y,Pb,Pr cable needs for the reason
mentioned above.
Y,Pb,Pr was invented for use in place of RGB to save on total bandwidth requirements.
Technically the term Y,Cb,Cr is for digital while Y,Pb,Pr is for analog (all consumer
products with component video nowadays) but often either is substituted for the
other."
Here's more...
"In practice, there should be no difference in performance although there may be
idiosyncrasies in the way two particular components behave such as the iScan versus your
TV. RGB is theoretically better but at the same more expensive and was impractical for
over the air broadcasting. RGB (which VGA is) is superior for computer data, but that only
has to travel a few feet from PC to monitor. There is no common video source material,
including HDTV, for which RGB will exhibit its superiority.
The reason why Y/Pb/Pr was invented was to save on bandwidth, only the Y (luminance)
carries the full resolution while the Pb and Pr need only carry much less, it is half the
resolution both horizontal and vertical for DVD, DTV and U.S. HDTV. Whereas video
transmitted via RGB needs full resolution on all three lines/channels/cables. When the
iScan delivers RGB output all three output lines must have the full bandwidth even though
the input might have been S-video with
effectively 1/4 the resolution preserved on the incoming chroma line that later becomes
the Pb and Pr.
Ultimately the video has to end up as RGB to feed the picture tube(s) or LCD panels. If
the TV takes RGB, converts it to Y/Pb/Pr for intermediate processing (mine does ^@#%%$!)
and then back to RGB, there is more of a chance there will be some idiosyncrasy compared
with RGB straight to the picture tube that a regular computer monitor does.
Roughly speaking, if RGB is red, green, and blue, then Y/Pb/Pr is red, white, and blue.
Slightly more precisely,
R is 1.00 red plus 0.00 green plus 0.00 blue,
G is 0.00 red plus 1.00 green plus 0.00 blue,
B is 0.00 red plus 0.00 green plus 1.00 blue.
Y is 0.30 red plus 0.59 green plus 0.11 blue,
Pb and Pr are also blends, I don't recall the numbers. Subject to the bandwidth of the Pb
and Pr and the preciseness of the blends, RGB can be regenerated perfectly from this.
Also of note, RGB comes in three flavors, RGsB sync on green, RGBS sync as a fourth
line/cable, and RGBHV horizontal/vertical sync. on fourth and fifth lines. The iScan has
some adjustment for this and needs to be set to match the TV. Y/Pb/Pr and S-video always
has sync on Y."
Allan has other video hints at his website.
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