Friday, December 28, 2007

Glittery things

There were a lot of things in the production of this movie that were responsible for it's rich tapestry of looks, but it is all too easy to forget that no post production took place.
While Roger Rabbit had the optical printer, the Thief came straight out of the camera, the way it was shot.
Also in the city, there lived a thief who shall be nameless...
Also in the city, there was some birefringence, which shall be called the Sellotape trick.
I am talking here about, what in computer terms is called, colour cycling.
The effect of coloured patterns cycling through all the hues in relation to each other is probably best known from the swirling background in the "Return of the Pink Panther" titles, but I think I am correct in assuming it is also responsible for the water effect in the fountainand most definitely the treatment of all the "gem effects" throughout the film.

Here's how it works:
The cameraman shoots the whole scene, camera-moves and all, but with the water area of the fountain painted black.
Film is rewound and the same move is shot again on the same piece of film, this time with a matte (black card or painted cel), the shape of the water surface, on the camera light box.
Behind the matte is a polaroid screen, (polarizing filter) that covers the matted area.
On top of this screen is a cel with the shapes of ripples stuck on from various layers of clear sticky tape (Sellotape in the UK).
Some 5 or 6 layers of tape have to be applied to get nice strong colours, so the whole shebang can become quite thick, which doesn't matter as it is all backlit and shadows are not an issue.
To the naked eye, this is still totally devoid of colours, but when seen through a second polaroid screen, turns into a veritable aurora borealis.
The second screen can either be a motorized filter that rotates on the camera or a second screen, applied to the top of the matte, the only important thing being that the cel with the tape is between the filters.
Polarizers restrict the light that falls through them to wave action in one direction only, that means, if you put a horizontal polarizer on top of a vertical one, virtually no light penetrates, rotate the top screen to horizontal and the screens become clear, the principle behind the display on your pocket calculator.
Stretched polythene, such as cling film (Ceranowrap) and sticky tape, has the weird property of twisting light that falls through them, but, and here is the trick, not all colours by the same amount.
So if for example enough layers are applied to twist red through 90 degrees more than green, than, with the filters above and below at right angles, no green penetrates, but red goes through unhindered.
If the top filter is allowed to rotate, the generated colours cycle through their respective hues.
A colour filter would be added to tint the whole effect. Blue, in this case.
The process is called birefringence, but we never called it that of course.
If any Rostrum camera person out there knows what they called it, please enlighten us.
There are added back lit water effects on top of these two exposures and there would probably have been some top lit effects as well but I'm sure we will come to some of those techniques later when we arrive at (what Dick called) the Star wars scene.
If you have children and come back from the Imax 3-D one day, with your pocket full of cheap cardboard 3-D glasses, get the Sellotape out and have some fun...
Your kids'll love it...


Aaron said...

Interesting technique.So for all backlight effects was it necessary to paint black matte shapes or could you just back light a cel that's painted normally to get the matte shape? Or did the water animation only exist as a series of black shapes that were given color through backlight filter process? And how many passes were necessary? Just the regular top lit pass and one fx pass or more depending on the complexity of the effect?

Jennifer said...

i love this blog!!!
thank you so much for doing this!!

Bert Klein

Michael said...

Hi Aaron
In most cases, the thickness of celpaint to cover the background on a top lit shot is not opaque enough to survive a back lit pass.
In commercials the cel is often backpainted in grey, but on this film most mattes were specifically produced and painted black.
If the water animation was back lit, there would indeed have been negative mattes for the animation and coloured filters for the colours.
They may however have been top lit, whereby the animation is shot on top of the background and then shot again on matte black.
The sort of glow achieved by this is limited as too much exposure will pick up the matte black backing and show up as a grey haze.
My Guess is that on a shot like this, there would have been at least 4 passes:
Top-lit BG and animation
Back-lit Polaroid FX
Back-or top-lit water
Top lit pass for colour correction or colour change within the scene, or transparencies of shadows etc.
How many passes there really were...
...who knows...

Michael Sporn said...

I've often wondered and guessed at how this effect was produced. Thank you for enlightening me. How simple, boring, and predictable it all is to do effects with computers. They aren't as rich. But they are easier.

Andreas said...

Hallo, Schlingel,
as always totally fascinated at your grasp of these things. no wonder you never had any problems with any of the new technologies.wish i had some of

LM said...

From "Inside the Yellow Submarine" by Dr Robert Hieronimus
pg 321

Charlie Jenkins:
I used to work with one of the illustrators that The Beatles employed called Marijke Koger [of The Apple Boutique and The Fool], a Danish art nouveau illustrator, did beautiful work. I used some of her work to make stained glass windows with a technique using Polaroid filters and light which transforms just regular Scotch tape into rainbow colors. When you turn the filters, all the colors change. I discovered this, I think by accident when I was working with Richard Williams. I assisted with some sequences for a film called Ivor Pittfalks, a short film which was never finished. I discovered that by working with Polaroid big filters that were used for the lighting in animation to get rid of the glare from celluloids, you put them on the lamps and the cameras. Having the filters there, I think it was just laying on the light box one day and I stuck a piece of tape on it to get it to hold it on the glass. I realized that by looking through the other filter these pieces of tape had a bit of color. I think it was red or something. When you turned the filter, it turned to blue. Oh, that was very nice. It turned to art work, transparent art work, just in Scotch tape. When you turn the filters, the whole thing lights like precious stones, like turns in all the colors in the spectrum.

Then I met Marijke Koger who did beautiful drawings of peacock ladies like the Mucha stuff. I had them printed into photo lights which are black and white and transparent, and then with celluloid fitted it into all the parts, and then shot them with a Rostrum camera through Polaroid filters, turning the filter with a motor. All the colors, all the details, changes its colors. It looks fantastic, like precious stones in the light. I did those for their concert for the Queen, the background for their concert. The backgrounds were back projected films that I did with this Polaroid thing, with Marijke Koger’s drawings. There was a whole thing going on in London in the 60s and 70s. If you wanted to do it, you could.
(Note: Jenkins stated in a later interview that Sellotape subsequently lost the properties that made this work.)