Film-Tech Forum ARCHIVE: Video Scaler Problem

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Posted by Martin McCaffery (Member # 37) on 02-08-2010, 02:39 PM:

Using a Extron 7SC with our Sanyo PLC XF40 to show a DVD at 16:9

When using the Extron switch to scale the picture at 720p some of the subtitles on the movie get blurred. Up close it looks like a line is drawn through them and the line moves back and forth horizontally. From the seats, it just looks blurry and unreadable. This is not happening on the rest of the screen, in fact it is not happening on all of the subtitles, just from slightly viewer left of center to about 1/2 of the right.

Switch to 480p and it does not happen.

Use the projector to switch to 16:9 from the 480p and again, no problem.

Does this sound like the switcher going bad, the projector, or just some strange DVD artifact to be expected now and then? Haven't had many DVD's with subtitles that we ran in 720p, but have never noticed it before.

Posted by Bruce Hansen (Member # 281) on 02-08-2010, 04:54 PM:

It may be just "normal" artifacts from the conversion done in the Extron. There is some strange interpolating that goes on, and the top and bottom of the image is considered somewhat unimportant, since it is overscaned, and not seen a lot of the time. I find that the best idea is: the less equipment you go through, the better.

Posted by David Stambaugh (Member # 1102) on 02-08-2010, 05:16 PM:

Is it a single horizontal line, or is everything from that line down to the very bottom of the image doing that? I know you said the rest of the image is ok but it might be easy to miss that kind of artifact continuing below the subtitles.

Posted by Steve Guttag (Member # 268) on 02-08-2010, 05:31 PM:

The System 7SC, though current, is a rather old scaler design. It is very much a 4x3 scaler. Its accommodation of 16x9 output rates is just that, an accommodation...it really wants to output 1024x768. I can believe you have scaler artifacts. I'm sure there could be an issue for the scaler dealing with the motion or 3:2 pull down and the static image of the subtitles.

Another artifact you may be generating is that you are taking the 480 source, scaling it to 720...then the projector has to rescale it back to 575 or so. It would be surprising if there weren't artifacts!

When using a scaler...KEEP IT TO A MINIMUM. Just like with gain...you don't want to do a little here, a little there...do it once and be done with it.

Since your projector is a 1024x768 projector...why not set it to that?

Steve

Posted by Martin McCaffery (Member # 37) on 02-08-2010, 05:52 PM:

Good to know. It's never been a problem until now (we don't do a whole lot). I'll make the appropriate changes.