[opendtv] Re: News: CEA FORECASTS CONSUMER ELECTRONICS REVENUE
- From: Olivier Houot <olho_avatar_i@xxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 13 Jan 2007 00:24:27 +0100
Bert,
Your HDTV bandwidth is for an uncompressed signal.
Where is the mathematical tool to compare
- an initial "704x480" analog SD signal occupying 6 Mhz of bandwidth
- a signal with a 1920x1080 resolution that has 6 times more pixels but
goes through a 50:1 compression step to finally force it down into the SAME
6 Mhz signal as its SD counterpart ?
Theoretically, there can be some doubt as to how much better the second option
is.
After all, shannon will limit the amount of information that you can squeeze
through this limited bandwidth in a given time interval.
And of course, a really significant calculation would be more tricky, as you
would have to consider the 10x horizontal color bandwidth reduction in analog
signals, the limitation of the luminance bandwidth to get room for color,
halved vertical colour reduction in european systems... Also, would you take an
initial 4:4:4 or 4:2:0 signal for HD? And which part of this information is
really significant for the human eye?
I am afraid mathematics are not the shortest way to the truth in this case.
A more significant test would be to use a setup with two large HD screens (that
means at least 2 meters) , one above the other, with upscaled PAL SD on the
first (a good upscaler like LetItWave's comes to mind) and true HD on the
second, both signals being provided through a selectable 6 or 8 Mhz bandwidth
channel.
It would be interesting to evaluate, after all the pain suffered to finally
make HDTV a reality, how much we have REALLY gained.
At least there is little doubt, when it comes to non broadcast applications
like blu-ray, that the public will have access to better picture quality.
The other topic was a comparison between PAL, specifically the UK
variety, and HDTV. The assertion being that there wasn't much
difference.
When all else fails, use math. The UK version of PAL, PAL-I, supports a
video bandwidth 5.5 MHz. The best PAL out there, PAL-D, supports 6.0 MHz
video bandwidth. Both of these are close to what NTSC can do with DVDs,
using the baseband video outputs. So that is (should be) what they are
most comparable to.
Other versions of PAL are 5.0 MHz or 4.2 MHz, the latter identical to
NTSC in a 6 MHz channel.
But HDTV is considerably sharper than any of these. Whether or not
actual receivers can make complete use of what's available, HDTV video
bandwidths are out in the 20-30 MHz region.
1080 at 60i or 1080 at 30p is 960 cycles/line * 1080 lines/frame * 30
frames/sec = 31.1 MHz.
720 at 60p is 640 cycles/line * 720 lines/frame * 60 frames/sec = 27.6
MHz.
I submit, a major difference between any analog scheme and HDTV.
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