Track Motion causes resampling even when it doesn't need t

RichMacDonald wrote on 2/16/2005, 4:46 PM
Just ran a test: Took a clip and set track motion to X=1.00, Y=1.00 with everything else unchanged. Rendered normally and again with the track motion.
The clip with track motion has significant softness, indicating that Vegas is resampling the clip.

Resampling is of course necessary if one changes the width, height, or rotation. But afaik resampling shouldn't be necessary if one is simply shifting in X and/or Y with an integer value.

Maybe I screwed up my test. Can anyone confirm/refute?

Comments

johnmeyer wrote on 2/16/2005, 4:55 PM
See my note in the script forum about smart resample.
RichMacDonald wrote on 2/16/2005, 9:27 PM
John suggested I turn off smart resample, but that made no difference. I've continued looking and now I'm confused:

1) With an interlaced sample the result was definitely soft, however I'm looking at the result on a computer and not a TV. (My TV is such junk I couldn't tell the difference anyway ;-)

2) I just tried the same test with a still and the project in progressive mode and the result was perfect, i.e., Vegas shifted the clip without any loss in accuracy.

I'll keep working on this. I hope someone has some time to run independent tests and double-check me.

One real gotcha. If resampling occurs in general (this remains TBD), then dinking around with motion tracking is dangerous. Even if you reset all track motion values to zero, if you don't also delete all your keyframes thenVegas will still apply the effect and soften the result. IOW a zero track motion still resamples if you have any motion keyframes on that track. Don't forget to run the script to remove all traces of motion keyframing.


Edit: Take the interlaced sample and look at it in the video preview window: In preview mode (auto or full), the track motion clip looks fine. In best mode (auto or full) yikes, the resampling is applied and the picture is soft. Can I render in preview quality :-? Let me see...yes I can and the result looks good! The preview quality render is better than the best quality render. Holy cow! My best guess is that the preview quality render uses a nearest-neighbor resample while the best quality render uses bicubic resampling, and in this particular case (a high-frequency picture) the nearest-neighbor does "better" because it keeps the high-frequency content. Big difference in the scopes too.

Edit2: I saved a Vegas project that hopefully demonstrates the phenomenon.
taliesin wrote on 2/17/2005, 12:27 AM
Looking to your project file I can state what you said. But I'm not sure this is based on resampling. I think resampling cannot work before the render. But the bluring caused by Track Motion is visible in the preview window even before rendering. So maybe the cause is different from resampling.

Marco
Liam_Vegas wrote on 2/17/2005, 1:04 AM
I see what you mean. That second frame is very soft in comparison to the first one.

I did one change that which appeared to work... and that was in the project properties where I set the "Interlace Method" to none. As soon as I did that the preview window view of that "moved" frame became as sharp as the original.

[Edit]... and I guess this means I don't really understand what that project setting does.... this is from the help file

Choose a setting from this drop-down list to determine the method used to render effects and deinterlace the two fields that make up a frame.

So.... is that setting just related to the Preview monitor.. or is it also applied when truly "rendering" FX? The help file just seems a little contradictory.

Hmmm... interesting.
taliesin wrote on 2/17/2005, 1:23 AM
Hey, that's it. I also tried to improve the result and changed the "Deinterlace Method" of "Project Properties" from "Blend" to "Interpolate". I know there are several fx besides of deinterlacing itself which depend on the "Deinterlace Method" settings. Sometimes there are differences in fx (I don't mean real deinterlacing) whether you selected "Blend" or "Interpolate" there.
Then I was bit frustated to see there was no difference here in that TrackMotion example.

But selecting "None" really did the job.

I whish we could have a better documentation about what some settings like this "Deinterlace Modus" does. It isn't that easy to find it would also affect things like TrackMotion.

Marco
Liam_Vegas wrote on 2/17/2005, 1:58 AM
I agree... this "problem" has really left me wondering what the heck that setting would really do to a project.

It might cure this particular issue... but would setting de-interlace to none have a huge impact on lots of FX's that you might want to use? I just <need> to know now.
farss wrote on 2/17/2005, 4:27 AM
The de-interlacing method shouldn't have any effect unless you are de-interlacing. So if all your footage is PAL DV LFF and you're rendering to the exact same thing Vegas I believe will never look at it.
However if you're doing a frame rate conversion such as going PAL to NTSC then it really comes into play.
But I have to agree the Vegas manual is pretty verbose but seriously lcking in technical detail. To this day I still don;t know what "Reduce Interlace Flicker" does precisely. I use it a lot because it fixes a lot of problems but as to hwy the problem was there to be fixed and how that switch fixes I'm still totally in the dark.
Maybe that's the one thing we should be requesting in V 6, better documentation!
taliesin wrote on 2/17/2005, 5:11 AM
>> So if all your footage is PAL DV LFF and you're rendering to the exact same thing Vegas I believe will never look at it.

But it does. Take this TrackMotion-issue as an example.

Marco