Track Motion verses Event Pan Crop

Former user wrote on 2/4/2003, 10:09 AM

I have a 2400 x 480 graphic that I'm using as an overlay on an open sequence. It is on a track by itself. My issue is that using "Track Motion", the graphic aliases badly, but creating the same effect using "Event pan crop" within the graphic clip itself gives me a very clean graphic. I have included two links to the frame grabs to illustrate what I'm talking about. You can see problem along the curved edges of the graphic element. The text on the graphic image is the entire height of the image. Shouldn't either method of "panning around" on a large graphic work? And BTW - This shows up in both VV3 or V4.

http://www.cox-internet.com/woodruff/vegas/track_motion.jpg
http://www.cox-internet.com/woodruff/vegas/event_pan_crop.jpg

Comments

mikkie wrote on 2/4/2003, 10:34 AM

My *guess* is that with the pan crop Vegas automatically resamples the picture -- be consistant with the way it handles clip frame sizes. If motion works better, what if you apply a slight blur to the still before importing it?

mike

jetdv wrote on 2/4/2003, 10:43 AM

Yes, I've noticed the same thing. It's like pan/crop looks at the picture while track motion looks at the current video frame. Here is what I do: If I want to zoom in on the picture, I use pan/crop. If I want to resize/reposition a video frame, I use Track Motion. When using pan/crop, make sure you right click the positioning window and choose "Match Output Aspect".

Ritchie wrote on 2/4/2003, 11:14 AM

Ah, I had this problem awhile back as well, however, didn't test the difference betwean Pan Crop and Track Motion.

Unfortunately I am not at home and can't check the exact settings, but somewhere in the settings for that event you can check a box that says reduce interlace flicker. That fixed nearly all of my problems. One of the SoundForge people also recommended going into your project settings and changing the project output/render? quality to best, because it uses a better resizing algorithm. I didn't test this myself though as I was satisfied with the results of the reduce interlace flicker.

Good luck.

SonyDennis wrote on 2/5/2003, 11:04 AM

That's how it's supposed to work. The signal flow is that the graphic gets resized using pan/crop, mingles with other events and FX on the track, and then the final result of the track gets composited over the track beneath it using track motion.

In this particular case, the signal flow using pan/crop on your graphic would be:

Select 655x480 portion of 2400 x 480 graphic, resample as necessary to 720 x 480 (DV resolution). This ends up doing a small amount of scaling in X only, no big deal. Composite this over track beneath -- no artifacts. The single scaling step is necessary to convert from the graphic's 1.0000 pixel aspect ratio to DV's 0.9091 PAR.

The signal flow using track motion looks like this:

Because there is no pan/crop, scale 2400 x 480 graphic to fit into 720 x 480 project size. This reduces the resolution to 720 x 131. Now, track motion blows it up and select a 720 x 480 portion, compositing it over the track below. Result: artifacts due to massive 3.6x scaling of done in track motion.

You'd think the two scaling operations that I listed above could be coalesced into a single operation, but there are a number of things that can happen between them, such as transitions, FX, opacity, etc., so they must remain independent operations.

Think of tracks as little factories generating 720x480 content for the compositer, which then composites everything together using track motion settings.

Moral of the story: Track Motion should not be used for zooming, that's not what it was designed for. That's what Pan/Crop is for.

///d@

Erk wrote on 2/5/2003, 12:11 PM

Sonic Dennis,

Thanks for taking the time with that explanation. Clears up some questions I had as well.

G

Ritchie wrote on 2/5/2003, 12:59 PM

Wow, is there a flow chart available that explains the order of operations in Vegas? I think it would be very interesting and possibly a useful tool in debugging our own user error.

jetdv wrote on 2/5/2003, 2:55 PM

How about page 42 of the manual?

SonyDennis wrote on 2/5/2003, 2:59 PM

Yes, search for "Video Signal Flow Diagram" in the help.
///d@

Former user wrote on 2/5/2003, 3:13 PM

Thanks for the detailed description. That explains the "issue" I was seeing. Obviously I was able to get the effect I was working for by using the Event Pan/Crop. In this particular case it would have much easier to use the Track Motion because I had multiple graphics to move (one dissolving into the next) and Track Motion would have let me apply a single "move" that could be tweaked as a single entity. Instead, I ended placing event pan/crop on each of the four graphics and timing the moves to coincide with each other.