[opendtv] Re: NHK demos UHD TV broadcast
- From: "Albert Manfredi" <bert22306@xxxxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Sat, 03 Jun 2006 18:24:17 -0400
Craig Birkmaier wrote:
>Think of it this way. In a cell phone image, If I quantize an
>8 x 8 block to a single value i will see a very visible 8x8
>block in the image (assume 240 samples per line, so the
>block represents 1/30th of the line). In a 1920 x 1080
>image, that 8 x8 block represents 1/240th of the line,
>thus it is only likely that you would even notice the
>quantization artifact on a VERY large screen.
Cell phone use typically QVGA in a 1.5" X 1.25" screen. So at equal viewing
distances, compression artifacts will actually be quite a bit MORE
noticeable in the HDTV screen than in the cell phone.
The cell phone's 320 X 240 screen needs 4800 8 X 8 blocks to paint the
image, or 2560 8 X 8 blocks per square inch.
The HDTV 1920 X 1080 display needs 129,600 8 X 8 blocks. Assuming a 45" X
25" display (which is 51" diagonal, so not all that large for HDTV), that's
only 115.2 8 X 8 blocks per square inch. Fewer blocks per square inch means
more noticeable artifacts, at equal viewing distances.
Sure, an HDTV screen is not viewed at the same distance as a cell phone.
Still, I don't want to lose track of real numbers. 2560 blocks/sq.in. for
cell phones is significantly more than 115.2 blocks/sq.in. of that 51" HDTV.
And the numbers are more skewed with 1280 X 720 HDTV, of course.
Higher resolution means more information in the image. With the bigger HDTV
screen, we can discern more information than we can in the tiny cell phone
screen. Similarly, in an even larger UHD screen one might expect that more
information will also be discernable than in the HDTV screen.
So, to get back to the original point, is their claim of 250 Mb/s required
for UHD transmission ridiculous, or is it plausible? If it's plausible, my
argument was that it would require a whole new compression alrgorithm to
make UHD a household term, just as H.262 was required for HDTV to become a
household term. Because you need to reduce that 250 Mb/s way down to make it
fit in standard TV distribution channels (which is what it took to make HDTV
practical).
You claimed 250 Mb/s wouldn't be required, because MPEG compression would be
more efficient and/or because we would not need so much more info than we
already get with HDTV.
Here are the relevant quotes from that article:
"NHK terms the technology as Super HiVision featuring 7680x4320 pixel
resolution with progressive scanning at 60 frames per second." And, "Using
16 MPEG-2 encoding chips, the signal was compressed to 250 Mbits per second
for transmission."
Did they take this into account your objections? Apparently, they did.
Scale up what it takes to transmit a 1920 X 1080 at 30p image to UHD at 60p.
All else equal, using H.262 compression, the 20 Mb/s HDTV transmission
scales up to 640 Mb/s. Yet, they only claim 250 Mb/s.
Basically, that's 32 times as much potential info (60p vs 30p, and 33 Mpels
vs 2 Mpels), transmitted with only 12.5 times as much channel capacity. They
must be taking into account that UHD screens will not be 16 times larger in
surface area than HDTV screens.
Bert
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