Mind blown - how is this done?

PistolPete · 2 May 2012 at 12:37

http://www.bbc.co.uk/news/uk-politics-17920260

I understand the principles of chroma keying, but how do they manage to move the camera around without any obvious signs of tracking markers and how do they get the graphics to appear in front of the presenter - is that a simple overlay? Again, how do they track it??

SteveOBHave · 2 May 2012 at 12:52

That is extremely cool - live green screening when done right is an epic tool. I do wonder if they track the cameras relation to the room rather than relying on position markers. That would make more sense to me.

PistolPete · 2 May 2012 at 13:18

Ah, never thought of that.

Andy90 · 2 May 2012 at 14:08

PistolPete said:
http://www.bbc.co.uk/news/uk-politics-17920260

and how do they get the graphics to appear in front of the presenter - is that a simple overlay? Again, how do they track it??

When they first remove the graphics and show the green floor, you can see a rectangle painted across the map of the UK. He knows that when he stands behind that box that the graphic overlay is in front of him and that when he stands in front of it, the overlay is behind him. Simply a case of positioning the overlay properly on screen.

Clever use of technology really.

PistolPete · 2 May 2012 at 14:46

Andy90 said:
When they first remove the graphics and show the green floor, you can see a rectangle painted across the map of the UK. He knows that when he stands behind that box that the graphic overlay is in front of him and that when he stands in front of it, the overlay is behind him. Simply a case of positioning the overlay properly on screen.

Clever use of technology really.

So you do..... however the tracking bit is still very clever.

alexthecheese · 2 May 2012 at 14:48

Yeah I think the tracking bit is the cool part, not the bits painted on the floor.

Andy90 · 2 May 2012 at 17:06

It is certainly nice and smooth, however I suspect it isn't much different to the technology employed in most modern 3D games, ie if you have a fixed point of view and rotate it or move it up and down, the background gets rendered and scaled accordingly.

Bearing in mind the computer that is doing this, doesn't have to render any other 3D models such as characters or work out that you've just been shot by a sniper 1 mile away

It would be interesting to see just how powerful the computer is that is running the rendering.

D.P. · 2 May 2012 at 17:19

alexthecheese said:
Yeah I think the tracking bit is the cool part, not the bits painted on the floor.

Lots of ways to do the tracking. For starters the camera appears to be in a fixed position on some kind of articulated arm and pan-tilt head, which will have encoders on them to record the angle the camera is pointing at.

The presenter isn't being tracked and if he was that is also very easy with such a setup, think what MS Kinnect can do on the cheap with a distracting background, a dedicated professional tracker with the green background will be very accurate. It is really only the camera angle. Even if the camera was being moved there could be overhead camera trackers, IR trackers, wheel encoders on the camera dolly.

gord · 3 May 2012 at 12:25

What would have been interesting is if they brought the graphics back on while you were looking at the back of the set or if he walked through the overlaid graphic.

So is the entire room mapped? That way it wouldn't matter how you positioned the camera, it's basically looking into a 3D environment. Then you've got him keyed in so you can still see him moving around the environment. Then you've got the overlaid graphic, which may work purely on the room mapping. I'm not sure you'd need positional tracking on him at all.

SteveOBHave · 3 May 2012 at 23:21

I'm more impressed by the lighting that they employ so as not to get inadvertent green 'bounce' off the presenter. That's why there's little perceptible fringeing on him.