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Shane,
I should not generalize on this subject, scaling is an art in addition to a science, Faroudja is the
perfect example of this. But a few general ideas could give this person a feeling for what to
expect:
Horizontally:
The 1280 horizontal pixels of a line of the 720p signal get converted to a line in the 1080i format
(with theoretical horizontal capacity for 1920). The resultant image would end up being displayed
on a device he already knows can not render over the 1200 horizontally for its technical
limitations. The horizontal interpolation of additional horizontal pixels (from 1280 to 1920, if
actually does that) is calculated and based upon scaler design decisions made from the existing 1280
original resolution, but all those added pixels, it can never increase the "original" resolution
(again, if the scaler bothers on doing that), and even with that they might actually never get to
the screen because of the tube limitations no matter how good the scaling circuitry could be. In
summary, the tube is the bottle neck horizontally, and a 720 signal "would probably" look as
spatially resolved as a 1080i signal.
Vertically:
Without knowing how the internal scaler/video processor of the Sony tube was designed one option
could be that each 720p frame "might" end up scaled down to a 540-line field to match the raster
speed of the 1080i tube, and use the following 720p frame to create the next 540-lines field of a
1080i image, one can imagine the video artifacts created if the video processing is not done
correctly to compensate for the blending of the two images. Another option is that the 540-line
images end up as individual 540x1280 progressive frames every 60th/s, less vertical detail but
keeping the plus of the progressive format, I do not believe the Sony is doing that. The magic and
secret of how this is done is usually proprietary and maintained behind body guards by each
manufacturer. The conversion could produce a loss in detail vertically in addition to the
interlaced artifacts introduced by the conversion, and if the video processor is poorly designed you
do not want to see that image.
Those are theoretical lines. We all know that we can never see the full 1080i lines of a 1080i
signal for technical reasons so the loss of vertical detail could be assumed to be worst than the
simplistic math above.
In other words, horizontally he could be OK because the 720p signal contains horizontal detail that
his tube display would be able to handle better than when feeding a full 1920 line of 1080i signal,
but vertically the conversion might suffer in picture quality in a more noticeable manner. However,
since his tube is relatively small I would not consider the impact to be as noticeable as viewing
the same on a 50+ set, so chances are that he would be OK vertically as well, unless his plays his
games with his nose touching the glass surface of the tube.
One final thought about both formats:
One has to remember than a 720p signal contains about 1 million pixels that record the action in
front of the camera, the next frame records another 1 million of whatever moved on the action, but
"of the same pixel position" of the image. A 1080i signal might have interlaced artifacts but it
captures detail of 2 million "different pixels positions". Imagine looking thru a mosquito screen
that has only 1 million holes thru which detail can be captured, versus looking thru a mosquito
screen that has 2 million holes to capture "different and finer" detail, granted in two phases of 1
million each but the human eye gets fooled as happening on one single phase of two million different
pieces of detail when viewing it. The key word on comparing these formats is "different pixel
positions" that provide "different" detail, most people concentrate only on the factors of
progressive/interlaced and speed.
Best Regards,
Rodolfo La Maestra
-----Original Message-----
From: HDTV Magazine On Behalf Of
M. Shane Sturgeon
Sent: Tuesday, June 07, 2005 10:02 PM
To: HDTV Magazine
Subject: More on the XBox/Sony question ...
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As a follow-up for the reader who asked about his Sony TV and XBox
compatibility, two more questions are posed:
"I will be purchasing the Xbox 360 when it debuts. Knowing that the Sony
KV-30HS420 converts a 720p signal to 1080i, my two final questions are:
1. When playing 720p games on it, will I be loosing picture quality?
2. If so, would it be drastic or barely noticeable? "
Thank you for your help,
-- M. Shane Sturgeon
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