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Basic Question re screen update speeds

#1
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6/2/08 at 10:34am
  • Joined: May 2008
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This is going to be a very basic question. There haven't been many occasions when I could examine an high-def TV screen outside of a best buy. One of the few such occasions was when I watched the Super Bowl this past January. I need a little clarifictaion on a display problem.

I'm sure you've noticed that odd phenomenon when areas in motion on the screen get fuzzy for a few moments. In the case of the Super Bowl, it'd be like this; Right before the snap, the camera's on the quarterback. Once the ball is snapped, there's a blur in the center action. Or, if the camera moves slightly, the crowd gets fuzzy for a moment.

Now, I understand that this may have been due to the slow response time of the screen's LCDs. I also understand that newer sets have faster response times. That's fine.

But when I see demos in the stores, it crops up in sports events more often than with movies. The question I have is this: does this phenomenon also crop up with broadcast HDTV, as an artifact of the compression algorithms used to get a high-def signal to the TV set? Or is it due entirely to the TV set being used?
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#2
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6/2/08 at 12:55pm
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Re: Basic Question re screen update speeds

Some of both, I'd guess. A plasma screen probably has about the fastest response time, but even they will have compression artifacts - the blurring on moving objects phenomenon that you describe.

Unless the broadcast has a super-high quality speed (least compression) there's little you can do about it. Oh, and by the way, most cable signals are more compressed than over-the-air signals.

--ignore the man behind the curtain

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#3
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6/2/08 at 3:48pm
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Re: Basic Question re screen update speeds

To answer your final question. I suspect it is mostly or entirely a signal issue. The bitrate of the signal. Not the TV.


They flutter behind you, your possible pasts.
Some bright-eyed and crazy, some frightened and lost.
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#4
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6/3/08 at 5:23am
  • Joined: August 2000
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Re: Basic Question re screen update speeds

Quote:
Originally Posted by chuckg
Oh, and by the way, most cable signals are more compressed than over-the-air signals.
And that varies by station. Our local NBC station devotes 1.8Mb of alotted transmission space to a 24 hour weather channel and 1.8Mb of space to dead air that used to be The Tube music channel. Another of our local stations just cut their bandwidth in half in what seems to be preparation for adding multiple sub-channels.

Most people won't know or just don't care. It's the few of us out in there that have to notify the local station that these compression artifacts are visible. The guy locally that measures this information via an ATSC video capture card regularly sends the stations e-mails with bit rate readings.

-Robert
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#5
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6/3/08 at 10:34am
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Re: Basic Question re screen update speeds

It is not unusual, if you are up close, to see that anything that starts moving becomes slightly less sharp, and sharpen up when it stops moving. Such is the nature of handling 1080i (and also 480i) material. The state of the art plateau is called motion adaptive de-interlacing where moving material is constructed using all even or all odd scan lines with interpolation of what goes in between while stationary material is constructed by combining even and odd scan lines from two adjacent fields for added picture detail.

720p and 480p material should not exhibit this behavior.

Less sophisticated processing uses interpolation all the time in which case moving material does not necessarily become less sharp but the entire picture is always less sharp than it could be. Also there are some lesser methods where the entire picture, if of stationary subject matter, may be as sharp as is possible but if something moves, a region surrounding it may become less sharp as well.

There are still better methods, but these are expensive and not very common.

Filmed subjects may become blurry when they move when the shutter speed of the camera is not that great.

Video hints: Line Doublers and De-Interlacers

.

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#6
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6/3/08 at 11:02am
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Re: Basic Question re screen update speeds

Thanks for all of your responses. Broadcast material's going to be of lesser quality than recorded material, so the glitches on things like football games is sort of a fact of life. (Good thing I don't watch football.) It'd be great if we could test out a 1080p screen with a DVD recording of a football game: if the blur-fuzz artifacts turn up _then_, then we can avoid that particular screen.
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