another motion tracking question…yikes

[Dave Allbritton]

Hmm, not sure of your specific issues, but I have found that working with time remap can help. Of course it all depends on many variables and your footage, however you should be able to key frame critical points of the window footage to match with your interior car footage. You’ll have to be careful not to “freeze” or reverse the re-timed footage. I personally get the comp (lets say the window footage) where I am happy, then I pre-compose and use time remap on the precomposed comp. Hope this helps!

BTW- if I have missed this completely, and your issue is more with the window footage reacting when the camera dips, you should be able to scale your window footage a bit larger (to later compensate for the camera dips) add a track matte the shape your window opening and key frame the window footage to correspond with the camera dips.

dave allbritton
info@daveallbritton.com
http://www.daveallbritton.com

[Jim Dodson]

Yes it is possible!! Simply motion track your handheld footage and then edit the “target track” to be your window reflection layer… then “APPLY” the motion tracking data to that reflectiopn layer

In motion tracking your handheld footage you’ll need to pick a good spot to track for example the door handle of your car — something with well defined edges and good contrast.

As for your keying problems, take a look at Andrew Kramer’s superb tutorial on greenscreening a car:

https://www.creativecow.net/articles/kramer_andrew/colorkey/index.htm

Jim Dodson

Quad 2.5 gig Mac – OSX

[Raine Parrish]

thanks for the response-I’ll explore your reply- what I’m trying todoshould be simple- get the window footage to track the car footage! But so far, it’s proven very tough!
rp

[Raine Parrish]

Yeah- his stuff is great- bought the DVD- but the green screen stuff has major spill.
Right now the car footage is the top layer and the alley (woindow) footage is below- showing thru the roto subtraction masks.
Everything is hand held.
I’ll look at your reply and see if I can figure it out.
Thanks
rp

[Raine Parrish]

BTW- I followed along with Andrew’s tutorial- stacked the layers just like his- and didn’t track. I have 2 shots that require tracking. One is a neon reflecion on the front window shield the other is alley footage flying past the open window.
Neither are tracking. Both have masks set at subtraction.

[Tony Kloiber]

Is the camera (appear to be) in the car with your guys? If so then the camera bumps along with the simulated car bumps? In that case the window footage would appear to be more stable relative to the car window. If the car bumps up then you would see more of the outside space at the top of your background layer (scene outside the car) and then the opposite when the car bumps down. There will be some motion blurring in the direction of the car bump motion on you background layer as well.

Use the window roto on a solid layer, use that layer as a matte for the background footage. Track the motion of the window layer and apply it to a null, parent the solid layer to the null. To use the y variations in the track as a variable for a vector blur on the background footage you might have to poke around a bit to figure that one out.

TonyTony

[Raine Parrish]

Man, I didn’t even think about that- thanks- you’re right- as the car footage appears to dip down- you would see more of the bottom of the alley wall outside of the window.
I’ve never attempted any of the techniques you’ve described however!
Just about everything after that advice is a….fast blurrr!
If you could point me towards a tutorial- or if you have the time and patience to explain further, I’d appreciate it a great deal.
Thanks again
rp

[Tony Kloiber]

Well assuming I’m right in my thinking here (I could be wrong, I have no example footage to verify my thinking) lets name the layer for clarity.

Footage of two guys in car against green screen = TwoGuys
Footage of street wising by used for filling in green screen area = Bkg
Solid layer = Bkg matte
Null layer = Well… Null

Ok you talked about rotoscoping, I was reading that as a way to improve the key. So I thought you had roto’d around the TwoGuys shot. Assuming that there isn’t a lot of movement of the camera independent of the TwoGuys shot the shape of the window should not change that much so.

Draw a mask (rotoshape) around the inside edge of the window (also assuming you can only see out one window). Disable this mask on the TwoGuys layer, you won’t use it here. Copy that mask and paste it to the Bkg matte layer.

The Bkg matte layer now has the shape of the window, but you need to add the movement of the TwoGuys shot to the Bkg matte (remember your simulated bumps).

Open the TwoGuys layer in the layer window (double click the clip) and setup a track. I’m assuming everything is the easy way here so you can us a single point tracker and get the x and y movement of the TwoGuys shot.

Pick a point on the window, some where that isn’t obscured during the whole shot and track it. There are a lot posts and links about tracking in AE if you have problems with it or it isn’t the assumed easiest track.

Once the tracking is complete and it looks like it’s matching the movement well, then apply the track to the target layer which would be your Null. People have lots of reasons to use a Null for the target of a track. At this point its kind of a habit for me.

In AE you can’t apply a track directly to a mask (rotoshape) so to achieve this you apply the mask to a solid (Bkg matte) and then the track is applied to a Null.

Parent the Bkg matte layer to the Null layer.

Now if everything was easy the solid layer should be covering the TwoGuys car window area and moving along with it.

Use the Bkg matte layer as a (wait for it) matte layer for the Bkg layer. You want the Bkg layer to be big enough that as the Bkg matte layer moves around it never reveals the edge for the Bkg layer. If you shot the Bkg layer with the same camera, lens and focal length and the scene filled the frame you’ll be fine, just watch out for the proportions of the two clips (Bkg and TwoGuys) if the relative sizes of objects in the two clips are very different you will have a hard time making a convincing composite.

To sweeten the composite you can feather the mask on the Bkg matte layer just a little (2 or 3) this will allow a simulated light wrap from the Bkg layer onto the TwoGuys layer.
Also If you had shot the Bkg layer with the TwoGuys layer (as one shot) the motion blur from the cars movement over the bumps would effect the Bkg Layer.

To get this motion blur you could use the Y axis information from your track of the TwoGuys layer and apply it to a motion blur (plug-in) on the Bkg Layer.
I’m not sure how to do it exactly but I would imagine that you might be able to write an expression that would give you the amount of blur relative to the amount of change in the Y direction. I’m just considering the vertical motion blur here to make it simpler as well as the assumption that there already is a great deal of horizontal blur from the forward motion.

TonyTony

[Raine Parrish]

Wow- this is an incredibly generous reply-thank you so much for taking the trouble to teach me this, very thoughtful. I really appreciate this. So, I’m gonna print this out and give it a go this weekend. If it doesn’t stink too bad- I’ll post the link for you to take a look! Thanks again – I’ll be diving in!
rp