What causes this vertical "jitter" on TV?

riredale wrote on 8/16/2006, 1:33 PM
I was going to label this "OT" but then thought that maybe there's a lesson here somewhere regarding burning our own projects.

Sometimes I notice on our NTSC big-screen Mitsubishi DLP TV that some commercial movies (shown on popular cable channels) seem to have a subtle "up-down" jitter every half-second. It's as though certain edges of objects in the movie jump up one pixel, then down. Since it happens every half-second, I'm assuming it has to do on a GOP level, but what's causing it?

The effect seems most noticeable on high-contrast lines that are horizontal, or largely horizontal. I don't think it has to do with the TV set, since other material looks fine. Could there be a tie-in with 3-2 pulldown, since it happens only to stuff shot on film?

Anybody have an official explanation?

Comments

Former user wrote on 8/16/2006, 1:37 PM
Probably related to the compression they used on the movie.

Also, sometimes the movies speed has been altered to fit in a certain time span. This will cause the occasional bump up and down.

Dave T2
farss wrote on 8/16/2006, 3:59 PM
Line Twitter,
nothing to do with compression. More to do with interlacing and / or having frequncies close to the Nyquist frequency going into A->D converters with poor low pass filters. You'll see it a lot on HD that's been down converted and even high res stills in SD video.
Bob.
Former user wrote on 8/16/2006, 6:15 PM
Or it could be that :)

Dave T2
autopilot wrote on 8/16/2006, 8:05 PM
"You'll see it a lot on HD that's been down converted and even high res stills in SD video."

So should these pictures be interlaced or de-interlaced, or maybe something totally different?
TheHappyFriar wrote on 8/16/2006, 8:56 PM
this is exactly that AA in 3d games was designed to combat. Maybe we need HDTV AA. :)
craftech wrote on 8/16/2006, 9:33 PM
The default settings on those units exaggerate the problem.

To minimize it try the following:

1. Turn off DefinEdge
2. Set Video Noise to Reduction
3. Set Contrast to 31 or less
4. Set Brightness to 46 or higher
5. Set sharpness to 0
6. View it from a distance of 9-10 feet if possible.

John