Weird herringbone pattern when cropping

Curt wrote on 10/23/2006, 9:09 PM
I'm using Vegas 5 and DVDA 2 to transfer old home movies to DVD. I've got the footage on my hard drive. I deliberately framed the shot so that the edges of the film frame are well within the video frame. I do this so that I can crop the frame later to get a nice smooth edged frame, since most projectors leave a pretty rough edge around the picture.

What I'm noticing is that when I view the cropped footage, I start to see a sort of pulsating herringbone artifact toward the end of the file. (This clip is about 30 minutes long.) When I start from the beginning, it's fine; but as it gets closer to the end, this crap shows up. Even if I start playback toward the end of the file, I see it, so I don't think it's a buffering issue.

Just to make sure I wasn't nuts, I undid the cropping, and the clip played fine.

This is not the first time I noticed this. I saw it on another similar project transfering VHS to Vegas.

My capture device is a Canopus ADVC1394. I connect a Canon MiniDV camcorder to its firewire port to capture film.

Any thoughts?

Comments

PeterWright wrote on 10/23/2006, 9:19 PM
I've had the same problem - especially when doing slight Cropping to lose a black edge - it may be that by only moving a few pixels in there's some field changing going on, but I'd love to know how to guarantee that this doesn't happen.

On one project - with hundreds of events - I gave up and removed all cropping, applied reduce interlace flicker and the problem disappeared.
MarkFoley wrote on 10/24/2006, 3:52 AM
This may or may not be releated...but when I crop my HDV footage it will always have the "herringbone" effect in the preview...but when rendered at "best", it all goes away....
Curt wrote on 10/24/2006, 8:26 AM
On the last project, I thought it would go away on rendering, but I don't think it did. I'll have to look at that.

I'll try the "reduce interlace flicker" trick, too. Did you say you had to do away with cropping to make that work?


Curt wrote on 10/24/2006, 12:41 PM
O.K. here's the latest.

I discovered that the file exhibits this problem even without cropping. Probably an anomaly in the A/D conversion process, since I never see it when dumping in DV footage. Anyway....

I did an experiment. I cropped the 30 min video clip to taste, still seeing the artifact in all it's glory. I selected "reduce interlace flicker." In the project properties, I told it to render at the "best" quality. Then I rendered the clip as an .avi.

The problem was gone in the finished render, but it took about an hour and forty minutes to render.

farss wrote on 10/24/2006, 3:04 PM
Have you tried specifying a De-interlace method in project properties?
In general if you're handling video from an analogue source cropping the image to fill the DV frame is probably not a wise thing to be doing anyway. For anyone watching on an analogue device you've now cropped off more of the image. A better approach I believe is to just mask the offending parts of the frame to solid black.
Thsi way when viewed on an CRT nothing is lost and when viewed on a LCD / plasma the uglies are just solid black. If intercutting DV and analogue the viewer will see the change in masking, that's the only downside I can think of.

Bob.
Curt wrote on 10/24/2006, 3:48 PM
The other thing I hadn't considered is using the "safe area" grid markers in video preview. That way, I'm only cropping the absolute minimum, or I may find that I don't need to crop at all since the black edges may be well within the overscan area.

What de-interlace method would be recommended? I know just enough about that to be dangerous!

farss wrote on 10/24/2006, 5:03 PM
Blend seems to be the recommended one.

The reason I mask out those ugly edges is just to save bandwidth when encoding to mpeg-2. You'll notice they're pretty dynamic so they must take up some of the precious bandwidth.

Bob.
Curt wrote on 10/24/2006, 7:33 PM
Well, fortunately it seems I can solve the problem in the final render. So I'll just go ahead and do all the other stuff I need to do (editing, adding music, etc), then make sure I have the right settings for the final render.

Problem solved!


fldave wrote on 10/24/2006, 8:56 PM
Deinterlace method: Try both Blend and Interpolate on short sections to see which one works best for you.

In general, the rule is slow panning/motion=blend; fast paced frame movement=interpolate.
Curt wrote on 10/25/2006, 7:22 AM
In that case, I'll use interpolate. We're talking about old 8mm home movies shot by rank amateurs. Some of the camera moves would make you downright seasick!