I’m suspecting it works better with environmental variations. If you had a colored cloak, the filmed color would shift based on ambient lighting, folding, shadows, etc, which might move it away from the keyed hue.
If what I’m imagining is right, what Cartooniverse is describing is a reflective coat (probably along the lines of the directional reflectors used in highway signs, also used for the Kryptonian costumes in the first Superman movie), and the camera has a ring light source around the lens projecting the chromakey color towards the cloak. That projects (say) green light, and every portion of the cloak visible to the lens reflects that hue back to the camera. I’d imagine this would give a more consistent hue to key off of for the matte. There’d probably be some color-correction needed for the stuff other than the cloak, but I think that’s fairly straightforward in movies today.
The (relatively) new digital video systems increased the popularity of green over blue for a pretty obscure reason. Some of the video algorithms (in particular DV) compress the blue channel **much ** more than the green. This means that if you try to key against blue, your resolution (and consequently the sharpness of your key) is much lower than the overall image. If you key against green, you get a much sharper key.
When all channels are merged for playback you can’t really see it but if you look at the blue channel of a DV capture, it looks like a really noisy/blocky JPEG.
The links below show the green and blue channels of some DV footage I’m keying (say hi to S/O trmatthe). The background is medium saturation green. Both images were saved with the same JPEG compression settings so the difference in image is not due to the JPEG format.
Given the trends in flat screen technology and the trends in miniaturization of cameras and video processing power, I expect this technology to be in specialized use as camouflage within the next 10 years, wide use in another 10, and it wouldn’t surprise me at all if it looked just as good as the crazy sci-fi effects we see in current movies in another 20. The technology to do so is simply incremental improvements of current tech.
Even an invisibility cloak that only provides 50% translucency with visual distortion while still is incredibly effective at concealment. And it looks like they’ve already got that.
With a few decades of incremental tech advancement, you probably could get an object to mostly vanish, from one point of view. But anyone looking from another direction could still easily see the object. To make an object disappear from many different points of view, each pixel on the object would need to be able to project different colors in different directions, and that’s something we’re still rather a ways away from.
Since it hasn’t been directly mentioned yet, I just wanted to add in that the reason for Blues-and greens is that people’s skin tone(particularly when reflectted on angle contains whites, yellows, oranges,reds, browns and blacks) And if you try to red screen or yellow screen you can get splotchy holes in people faces.
The reflective technology(I think the first company was Holosuite, at least they were the first I used) rocks. It’s a highly reflective fabric that reflects the LED light with a high and consistant intenstity and color back to the camera, regardless of angle. Fabrics that arn’t as consistantly reflective can send back variations of the color in wrinkes and folds, which makes keying out much more difficult, since you need a wider range to key.
It permits normal lighting and camera movement. Travelling mattes are achieved ( or, were before c.g. was invented ) only with motion control cameras and the frequent use of track points on a green screen. With this new system, you are freed of two important restrictions. A) A Green Screen studio, and B) Very flat even lighting. Traditionally, the exposure must be perfectly equal across the entire area being matted, or the matte cannot pull properly.
And finally, Welcome to the Straight Dope, trmatthe !!!
Cartooniverse, is ChromaFlex the fabric in question, combined with a LiteRing?
This would key out the fabric, but something else still has to be put in its place, how was that done, a pre-existing motion-controlled camera shot?
Exactamundo !!! I got to play with it again this past weekend south of Boston at a trade show. Yeppers.
The way to key in the background a la Harry Potter is a beamsplitter and dual magazine camera. Expose the IDENTICAL image onto two strips of film. “Key” out the lovely and now-rather-buffed Harry and insert the same footage from the other magazine.
I will admit that a beamsplitter camera is too bulky for a Steadicam. I think I can find the Steadicam Op through my contacts who shoots those films. I’ll email him and ask him if he used a standard camera body or not.
