Blue Screen


Dear Mr. Stapleton,

I've recently watched the Ingmar Bergmann B&W movie 'Wild Strawberries', when I
came across a (for me) common question. Near the end, the old man is sitting in his
car during the day. The car and himself are lit by the sunlight (probably
not real sunlight), and then all of a sudden everything blackens and the
light is only on the man. The background is in dark, expressing his
loneliness and isolation. How is that done?

Thank you in advance.
Jan Wilm

This could have been done in one of two ways. All the car stuff in the movie used back projection for the views outside the windows of the car. This used to be done before blue screen came along. Back projection is still used occasionally as it means when you finish the day the work is “in the can” - no costs in post. I have used it many times, as recently as 2000 for a driving sequence in Buffalo Soldiers. This time I used video back projection as it was a night sequence and did not require the kind of detail and resolution that film gives. I did the same thing in Kansas City.
So back to the question. I looked at this a number of times. The interesting thing is that the background fades out uniformly. If they used plates for the trees etc in the deep background and had the kids at the window of the car and the old man sitting there, then they faded out the plate and the light on the kids at the same time, leaving the light on the old man. I suspect this is what they did. The plate may even have been a still or a painted backing as the trees don’t move. There is a tiny bit of light left on the elbow of one of the kids which is why I think it was done this way. The other way would be to shoot the kids, the window of the car and the BG as a plate and then sit the old man in front of it. This would mean the actor would be talking to the kids on the projection (!) ; then fade out the projection. Being in B&W, this type of fade would not suffer from the increasing warmth as you fade out. If you did this in colour you might want to use shutters/blinds to fade the lights so the colour temp does not drop.
There is a slight possibility that it was done in post using an optical fade on the selected part of the picture but Bergmann is such a good director that I’m sure they pre-visualised this idea!
Thanks for an interesting question and the opportunity to view a Bergmann film I hadn't seen.

As a DP, I'm in the planning stage for a low-low-budget short set in daytime on a train during the 1940's. Since this is a noir-adventure-period movie, we will shoot it in B/W on Super-16. We will use back projection and rock the set to create the illusion of movement. And here the trouble and fun begins...
My first question: in order to save some money, would it look like crap if I shoot the plates on progressive-scan video (like CineAlta or similar)?
Second question: while shooting the plates, is it wise to overexpose them in-camera to achieve a "semi" blown-out effect on set?
Third question: some shots will be in slow-motion (it's an adventure flick, remember…), and this will cause sync-problems with the back-projection. Since it's on B/W we can’t use chromakey (we don't have any CGI-money either), and I think it would be a too obvious cheat to totally blow out the windows just during these shots. Any suggestions?

Unfortunately you didn't tell me if the back projection is on film or video. Lets assume it's video, with video projection. If you are in the USA then you have the problem of 24fps in the camera and 30fps for the video. If we are doing this professionally then the video can be changed to 24fps so there is no rollbar. However, there are other ways that are coming into play now. There is an in-line gismo that somehow gets rid of the scan lines and enables you to shoot at any frame rate. There is also LCD projection that doesn't scan in the same way.
In order to figure it out you need to do the following:
Find out what video system for shooting the plates may be available. Get a test tape from this system and find a projector to put it on. Back-Project the picture to a size at least 9'x6'’, or whatever you think will cover your shot(s). The screen needs to be at least 6’ back from the train and preferably more. This is to allow you to bring in “interactive” lighting through the windows to hit the actors and interior of the carriage. This lighting obviously must not hit the screen in any way (and ruin the blacks). Unfortunately there is no “gismo” that will substitute for a film test, as far as flicker is concerned. You just have to assemble the components and try it out. Even at my exotic level of film making, we still have to do this as there are so many factors that can come along and mess up the shoot.
Shoot the plates normally, but then make the projection bright (one or two stops) in relation to the foreground lighting. You might like to think about filtering the plates if you intend to filter the scene... Or test this aswell. The thing about tests is that you don’t need to shoot more than a few feet of film: most of the work is in making sure all the components work together and not embarassing yourself on the day by being ill-prepared.
By the way, viz-a-viz the b/w, if the film is to be seen only on tape you may get a better result shooting on colour (500ASA which could be useful) and turning it to b/w afterwards. Or not.
Good luck!

When actors are not filmed against a blue/green screen or other nuetral background, how are computer backgrounds superimposed directly behind them?
Rob LaPoint

The answer is: with difficulty! The technique is called Rotascoping and involves a painstaking frame-by-frame extraction of the actor from the original background, then matting him or her back on to the new background, then adjusting things like contrast, colour and motion blur to suit the new background. Things like long hair are a particular dread of the matt artist in this situation.
If you have access to a laptop with Photoshop installed, you can have a go at his yourself with a still image, and you'll see how hard it is to create a convincing combined new image - and that's just for one frame, not 24fps!

On commentaries on the DVD's, they sometimes mention the use of a blue screen, to fill in the background at a later time. But they also mention the use of a green screen for the same purpose. My question is: what is the difference between blue and green? Do they have a different effect in the end? ??--Stephanie

No they have no effect on the end product. They are interchangeable and the choice is more to do with the colours in the foreground. If an actor has on a blue coat, guess which screen makes more sense! Black and white are also used on occasion. Every year the CGI people tell you something new about how they want screens, because the technology they are using to "pull a matte" changes all the time. Sometimes they just say: Don't bother using a screen at all!

Animation Techniques
Bleach By-Pass
Blue Screen/Back Projection
Books to Read
Budget Considerations
Car Photography
Cider House Rules
Clubs etc
Digital - Scanning
Director/DP Relationship
Dp's - where to get them
Exposure Techniques
Exterior Shooting
Film versus Digi
Filming Monitors
Frame Rates and Digi
Framing Techniques

Future Outlook
Jobs in the Industry
Learning Film Technique
Lighting Issues
Multiple Cameras
Panic Room
Picture Quality
Pre-Production Testing
Production Designers
Slow Motion
Special Shot Techniques
Student / Career
Super 35 versus Anamorphic
The ;Look;
Timing/Grading Issues
Women's Issues