Pan Crop and artifacting

PeterWright wrote on 2/10/2005, 9:36 PM

My almost-pensioned-off DV camera is one of those which shoots with a thin black line up each side of the frame a few pixels wide.

Normally I ignore this as it cannot be seen on TV, but a recent project is also being output on CDRom, so I decided to do a slight Pan/Crop to lose the black edges, keeping the aspect ratio the same.

The resulting render, when output to tape, had some artifacting - mainly a couple of thin horizontal bands near the centre which "swayed" every now and then, like a hula dancer's hips, only far less attractive.

I went through and restored the pan crop on every event (wish I could have done 'em all together!) and the picture was back to its former excellence.

So the question - when cropping like this, are there other things, such as force resampling, supersampling etc, which should also be done to avoid these artifacts?

Peter

Comments

Spot|DSE wrote on 2/10/2005, 10:04 PM

You've probably created a field error when you did your pan/crop. There are quite a few posts on this from somewhere in the past, and nothing will fix this if you are manually setting it and shifting a field. It would be nice if Vegas had a way to catch this for you, but it's a problem in many applications.

PeterWright wrote on 2/10/2005, 10:17 PM

Thanks Douglas - is this caused by "starting" the new rectangle at the wrong place vertcally - in other words, if my crop rectangle was one field (one pixel?)"higher" up the frame, it should be better?

Peter

Spot|DSE wrote on 2/10/2005, 10:23 PM

Exactly. One field up or down. I keep meaning to do an article on this, in the footsteps of Rich Harrington's excellent FCP article relating to the exact same prob, but I'm too lazy.

PeterWright wrote on 2/10/2005, 10:30 PM

Thanks - now, the pan Crop preset I have been using has position co-ordinates of X = 359.9 and Y = 287.4, so should I change Y to say 288.4, or is it the "part pixels" setting that could be contributing?

And incidentally, I couldn't think of you as "too lazy" - If I had three lives I doubt I'd get through what you do!

Chienworks wrote on 2/11/2005, 3:22 AM

It seems to me that if you crop in slightly, you'll end up stretching, say, 476 vertical source lines over 480 vertical output lines. It seems like no matter where you start the top of the image, you will end up with numerous lines being spread over the wrong fields in a varying pattern. If you have source line 2 on frame line 0 it's fine (even to even), but as you progress down the image this will get out of sync. By the time you reach source line 119 it's being displayed on frame line 120 and is now in the wrong field.

Or is Vegas more intelligent than this?

My personal opinion is that i would rather have the barely noticeable black lines around the edges than to have the artifacts that cropping produces.

PeterWright wrote on 2/11/2005, 4:47 AM

> "i would rather have the barely noticeable black lines around the edges than to have the artifacts that cropping produces."

Yes, Kelly, that's the conclusion I've been coming to - it was such a relief to get my decent looking footage back again, but I thought it worth investigation in case there was a simple "cure".

Peter