[New to AE] Tracking a key in the background of a moving shot

[nem2201]

Now I've done plenty of normal keying work before but I've never used a key as a "prop" per say. Also its not a green screen...

So we arrived on the shoot and I intended to have everything shot "in camera". We had a real projector that I was going to use to project an image on a white screen. Unfortunately luck was not with us that day and the bulb burnt out before we started shooting. I decided I would try and edit in the projection in post.

Using Premiere I was able to achieve some success at keying out the background in the static shots.

But then we have the final shot of the scene which features a character walking in front of the screen and a pan to the left. I've tried just creating key frames with the position in Premiere but the movement proved too jittery to look like the key belonged in the shot.

Now I'm an utter novice at AE and I've been scouring for tutorials but haven't found anything that might help. I'm assuming this could be fairly simple but I'm drawing a blank. Maybe you folks could help?

[Roei Tzoref]

can we see the video so we can examine and suggest a reasonable workflow? how long is the shot? is the camera moving? if you need to cut a character from a semi-noisy background this looks like a job for Rotobrush.

you can read about it here: Roto Brush and Refine Matte in After Effects

[nem2201]

Heres the source video. https://www.youtube.com/watch?v=fGQ4Zpt8FJk&feature=youtu.be

YouTube

[kirkeric · Accepted solution]

Hey thanks for the source video.

So, based on what I see and the length of time, the roto is your likely best course of action in AE.  I took the liberty of testing one of the more complicated portions where his hand goes in the screen.  The body will roto easily.  The hand, I wanted to check.  There is also the need for some minor tracking a bit later when your camera moves, primarily of course to place your image on the screen.

So, I duplicated layer, roto'd just the arm that gets in the screen, added a Refine Soft Matte as seen in the attached image, then added the image between.  For a few minutes, not bad.

Sample - YouTube

Let me know if this helps.

Eric

[nem2201]

This is fantastic thank you. I've started the roto process and it's much easier than i anticipated, it just takes time to render.

Do you have a tutorial I might be able to follow to apply the tracking for the image? Thanks again of your time.

[kirkeric]

Good deal.  Glad it is working for you.

I'd guess that the AE Camera Tracker would probably work great for this shot.

This looks like a good tutorial on that. 3D CAMERA TRACKER - After Effects Tutorial (Easy) - YouTube

It should give you some nice points toward left side of screen and the little projector might be a good spot to pick up some track points.

The AE Tracker locks things down pretty darn good.

Also, spare yourself some time by duplicating the layer, chopping it down to the area where camera begins to move so you aren't tracking the entire length.

Eric

[nem2201]

Hey Eric,

Never could get the 3D Camera Tracker to work. Went through a few troubleshooting guides but in the end it would just freeze at somepoint during the analyzing and couldn't get past the frame. The fact that it was a different frame everytime makes me think its my computer not the program.

Anywho I think I got it to work pretty well with the AE Tracker except for one problem...

So yeah... hoping I don't have to rotoscope again, not sure what I did wrong.

[kirkeric]

Hello Nem,

So, just to understand what I'm seeing here, it appears that he is not roto'd out in this particular spot?  You mentioned the camera tracker issue but the picture seems roto related.

Roto is never fun.  The issue I'm seeing in this still is he's not roto'd out and I also note, the projector is not masked out.

What else can you tell me to better assist?

Good to hear back.

Eric

[nem2201]

Here is the mask I made with the rotobrush. I tracked this layer with the simple AE Tracker which seems to work fine but the painting appears to fill in the black space and not on the screen.

[kirkeric]

Hello Nem,

Have you figured this out yet?  What I would have done for this entire process is 1) Roto just the man who crosses the screen (placing his layer on top).  2) Used the AE Tracker not on the mask but rather on the scene, particularly using track points around the screen and the projector to place the image on.  And then 3) I probably would have using mask tracker to cut out the area where the projector overlapped the image.

The most tedious part would be the man but I think you have done that.

Eric

[nem2201]

I should note that I've tried using Mocha as in this tutorial Learn Tracking and Screen Replacement with Mocha for After Effects in only 6 minutes! - YouTube

but it seems whenever my actors steps in front of the screen it skews the tracking points.

[kirkeric]

Hello,

I'm just arriving to the forum, however I've actually dealt with this very thing on multiple occasions where someone is walking in front of the screen.  In my cases, it was repeatedly walking across the field of view of a laptop sitting on desk.  The problem being the same.

I too would be curious to see the video or at least know the length.  Not knowing that, I'd offer this.  The short answer ranges from simple manual keyframing a mask to tracking movement and applying a mask, to a roto job as mentioned.

Personally, if the gentleman just makes a couple passes through over a short period of time, manually masking around him works pretty well.  The movement can actually mask (no pun intended) much of the line.

In simple terms, this amounts to duplicating your layer, then masking around the man in the areas that he overlaps the screen.  With straight and slightly rounded edges around his waist and face, it's not too much of a task, however clearly this can become more difficult if this is going on for an extensive amount of time.

As Roei mentioned, the roto is an obvious method too.

There are other tools such as Mask Tracker for AE but don't want to boggle you with too many options right away.

v/r

Eric