how to improve quality of panned/cropped (zoomed) video?

jeh wrote on 6/24/2003, 5:26 PM
Zooming out works fine. However, if I try to zoom in and do a little panning, the resulting rendered video looks awful. There are thin horizontal black lines that lead and follow any rapidly horizontally moving object (person). It might do something similar for vertically moving objects, but I don't have any. :)

I realize that I am trying to fill 720x480 pixels with somewhat fewer pixels here, the equivalent of "digital zoom" in a still digicam. But, sheesh, a still digicam interpolates between the pixels a lot better than this!

Similarly, if I take a 360x240 jpg and "increase image size" in Photoshop, or even little old PaintShop Pro, I don't get artifacts like this. I do get a bit of blurriness (of course), and I expected that in the video too - but I figured I could tolerate the loss of resolution for brief shots - esp since the subjects are moving rapidly anyway, and this project is just going to end up on VHS. But I can't tolerate these ugly black lines. The result is unusable. In fact I don't see how on earth can anyone use this as it is.

I tried keeping the zoom ratios low (no more than 2:1). Didn't help. It even shows at a very modest zoom ratio like 1.3:1.

Is there any way to tell Vegas to "work harder" to interpolate this stuff? I'm already rendering at "best" quality.

Hmmm.... I don't suppose there's any reason why "track motion" would work any better than "event pan/crop" ?

Comments

Sab wrote on 6/24/2003, 6:49 PM
You're likely to get a lot of suggestions on this one. Here's what we do.

Photos are scanned at 655x480 - 150dpi or a higher multiple of those dimensions if you're going to do a lot of zooming (2:1 is a pretty substantial zoom for video). For subtle zooming or panning, 655x480 works really well. Stay at the best setting for optimal results.

Photos with a lot of tight busy patterns usually require re-sampling which is a switch on the event.

Mike
jrlogan1 wrote on 6/24/2003, 6:58 PM
It sounds like you aren't complaining about the resolution of the zoom, which will obviously degrade the closer in you get, but that you are getting artifacts. I have done lots of pan/crop zooming on both stills and video and never had even a hint of a problem with vegas. I know this doesn't solve your problem, but it does tell you that there must be something wrong in your setup somewhere.
I agree with mike, you can try resampling the events you are zooming. You can also try the other switch, reduce interlace flicker which is sometimes helpful.
Do you get these artifacts in the preview window while working in the project, or only in the final render? That should give you a clue where the problem is.

Good luck,
Jon
AZEdit wrote on 6/24/2003, 7:25 PM
I posted a video presentation that was done entirely with V4 Pan and Zoom. I think the images look fine... it's a little large, but if you have the time...

You need to digitize, scan or shoot your stills at a higher resolution to give you room to zoom into the pictures. Also, I have used pan and zoom on video and went in pretty far and still looked very clean...

http://www.vegasusers.com/vidshare/textdisp?azedit-johnsonbank
Chienworks wrote on 6/24/2003, 7:44 PM
I think you're zooming in on video clips, not stills, right? What you're probably seeing is the problem that when zoomed in, the scan lines that would normally appear only in their own interlaced field can now appear in both fields. Changing the clips' properties to add Reduce Interlace Flicker should help. This will combine the two fields together either by blending or interpolating (as specified in project properties) and help fill in the empty scan line areas that you see as black lines.

You don't see this problem with stills or progressive video because they're not interlaced.
The_Jeff wrote on 6/24/2003, 10:10 PM
deinterlacing may help. Setting reduce interlace flicker may help..

But, I am pretty sure that reduce interlace flicker does NOT actually deinterlace the video. I think it applies a soft blur effect in the verticle direction with the "other" field but it does not appear to be impacted by the "deinterlace method"

The deinterlace method only applies when vegas is trying to reder interlaced video as progressive.

Chienworks is of course pretty respected here and I am mostly a lurker so I could be wrong. Documentation could be better here..

But try this.
Take a short video segement (interlaced) turn on reduce interlace flicker.
render as interlaced mpg with the deinterlace method blend.
do it again with deinterlace method interpolate.

The resulting files are identical (via diff command..byte by byte comparison).

Futher evidence.

http://www.sonicfoundry.com/forums/ShowMessage.asp?ForumID=4&MessageID=175567

http://www.sonicfoundry.com/forums/ShowMessage.asp?MessageID=94138&Page=0


Having said that, it might still make sense to deinterlace that video segment before using it. Try using a one of the smart deinterlacers from something like virtualdub.


Chienworks wrote on 6/24/2003, 10:42 PM
Jeff, well, to be honest, i wasn't sure what this would do either. I tried zooming in about 4:1 on a DV clip and then panning across the frame. This produced some noticeable black lines around high contrast edges. Then i turned on reduce interlace flicker and most of the lines disappeared. The image did get slightly softer too. Blend seemed to help more than interpolate, and this seems sensible to me since i was zooming rather than changing the speed (spatial alteration rather than temporal alteration).

I only made a visual comparison, but the difference did seem to be there.
PhilHemel wrote on 6/25/2003, 1:03 AM
I was getting HORRIBLE artifacts and 'wobbling' on pans and zooms until I selected 'Interpolate Fields' in project properties.

I tried all 3 deinterlace settings with and without Reduce Interlace Flicker and Interpolate Fields gave by far the best results.
jeh wrote on 6/30/2003, 9:10 PM
Thank you, chien, jeff, and phil - "interpolate fields" or "blend fields" does the trick, depending on the speed of motion.
musicvid10 wrote on 6/30/2003, 10:24 PM
I would deinterlace first in VirtualDub using Donald Graft's Smart Deinterlace filter, and then proceed (rendering in Best mode), or use satish's frameserver to do the same. But then I am a bit old-fashioned, as has been amply demonstrated in previous threads. . .