www.ssontech.com

peterspence · Joined: 15 Aug 2008 Posts: 5 Location: Oslo

I find myself in the luxurious position of having some time to do some tests for an upcoming VFX shoot for a feature film.

The basic scenario is one of a small animatronic character needing a digital head replacement. I'm currently testing different options for tracking points to get the best data possible.

The character has a very small head (about 8cm high by 3cm wide) and will be carried by an actor - often quite roughly. I'm considering whether large, prominent markers would be better than many small discrete ones. I'm currently experimenting with LEDs and fibre optic cable to get a point-cloud effect.

Any experiences / advice?

Kind regards,

Peter Spence
Visual Effects Supervisor
Qvisten Animation

ssontech · Posted: Wed Aug 20, 2008 8:49 pm Post subject:

Beware point light sources smaller than 1 pixel in size, all sorts of bad things happen in the camera electronics and compression. You're better off with some sort of uniform diffuser at the end that increases the point size to a few pixels across. Some sort of plastic bead on the end of the fiber, maybe (or right-sized LEDs)

peterspence · Joined: 15 Aug 2008 Posts: 5 Location: Oslo

We're actually shooting either 16mm or 35mm, so I'm hoping that we can get some pretty clean footage back. We're running a test shoot on Monday to check for film grain issues.

Thanks for the Tip tip. I'll experiment with diffusing the light at the end in to a bigger dot.

When it comes to tracking these bright points, is it recommended to blur the footage first? (We'll be working with 2K footage, so the level of detail should be ok.)

Kind regards,

Peter Spence
Visual Effects Supervisor
Qvisten Animation

NickJushchyshyn · Joined: 14 Aug 2008 Posts: 3 Location: Philadelphia, PA

[EDIT: ARGH ... sorry ... didn't realize this thread was so old.]

I'd recommend against blurring ... especially since you can down-rez in Syntheyes if you really feel the need.

Is the animatronic head to be completely replaced?
If so ... green LEDs or fiber tips on a black base would be a good way to go.

The physical size of the marks in the real world are secondary to their pixel size in your finished film scans. Ideally, the marks will be a few pixels in size or larger. If they're moving quickly, you should prepare yourself for a good bit of roto-tracking (using the mouse and/or numeric keypad to manually track through the motion blurred marks)

Make sure your markers are completely ridged in relation to the skull of the character ... and shoot some slow "survey" plates (turn table) of the head so you can use Syntheyes to build a 3d model of the marker relationships which will make 3D tracking your shots MUCH easier.

Don't forget to shoot distortion grids so you can undistort the shots easily to take lens distortion out of the mix when solving your shots.

peterspence · Joined: 15 Aug 2008 Posts: 5 Location: Oslo

Nick,
Thankyou for your reply - not too late at all! We finished shooting principal photography a couple of weeks ago, but still have some second unit stuff to do in a few weeks.
All tips are good tips!

Distortion grids are an excellent idea that I had overlooked. We'll be using the same camera set up for the last round of shooting, so hopefully I can get something useful there.

The diffused tips of the fibre-optic cables worked fantastically! I've done a first batch of tests and the results were rock-solid. The main stretch of post work starts in January. I'll try to update the board with some examples once I get clearance - nothing before next year though!

Kind regards,

Peter Spence
Visual Effects Supervisor
Qvisten Animation