T.V. Replacement

[Zander]

i was just talking to one of my professors, and he recomended not eve green screening and just use tracking dots to place the image (simaler to andrew kramers tutorial)

would this work (assuming nothing crosses the plane of the TV

[Joseph W. bourke]

Zander –
Your prof is right. I did one of these projects a couple of years ago, using Combustion, but with a long, sweeping shot done with a motion control camera rig, which meant that we could reproduce the shot perfectly over and over. I would suggest you use a motion control rig if you can afford it; this will allow you to use the coordinates directly in your software (no tracking necessary). If you can’t, use the tracking dots (I think we used 9 on each TV set (make sure there’s one in the center of the screen, plus ones at top center and the very edges of the corners). We used bright orange dots that they sell at office supply stores.

What I did to track each TV (the people who did the motion control rig on my project neglected to save the tracking data, or were too lazy to save it – I’ll never know) was to first go to the middle of the tracking shot, where the screen was as close to full as possible, and do a frame grab. I then brought the grab into Photoshop and cut a master mask, to track to the TV. That way, I could replace the footage very easily in my compositing app (which happened to be Combustion, but AE should be able to do the job).

Be prepared for time-consuming project. I had to track much of the project by hand, frame-by-frame, with multiple tweaks of the mask to get it to look perfect). It definitely helps to stabilize your footage first, just to get any bumps and dips out of it – this will make your track smoother and more believable.

When you’re shooting the footage, since you’ll only get one final master shot, make sure you pull focus on the dots, or you’ll really have a nightmare on your hands. With a motion control rig, you can do two identical passes – one with pulled focus for tracking and with lighting on the tracking dots to make the tracking easier (it’s real tough to track an out of focus dot), and one with the final lighting and depth of field for the final pass with effects, gleams, and anything you need to add in post. Without the motion control rig, you have to compensate for any low-key lighting you might want to have by making sure the dots are sharp, lit, and in focus. It’s a compromise, but you have no other choice, unless your shot is very simple and you can get extremely close to reproducing it. This might give you the chance to pull a track, then drop it into the final shot with a few tweaks.

The main reason you don’t want to do a green screen is that with the reflectiveness of most sets, you’re bound to get some green reflections or hightlights, which will add a whole other color correction project to your already complex project.

Anyway, good luck with the project. It will really hone your skills!

Joe Bourke
Art Director / WMUR-TV