Cinematography Mailing List - CML

Car Rear Projection


Hi all,

I want to shoot a car scene via rear screen projection. My experience has always been with greenscreen.

I am interested in any ideas on this, although my main points of concern are:

1.) What projector and screen to get?

2.) How much space I'll need?

3.) Is there a screen that might wrap a bit if I want a camera move from side window to front window?

4.)Lighting the car for day (city with buildings) and night and what kind of light moving devices are used/ available?

5.) How camera should be rigged when shooting from outside the car to give a nice realistic aesthetic movement and feel? -And not to feel bolted to the hood of the car.



Tom Peters wrote:

>>I want to shoot a car scene via rear screen projection.

Adding to Mark Weingartner's great reply...

I've only used LCD projectors from Background Images - formerly Background Engineers (LCD's = no sync cables needed). Tweaked to tungsten - good color and strength perfect with DigiPrimes t1.6 to 2 - in fact we had to fight to keep it from getting too warm on the day/ext plates. HD primes wide open is your friend on RP.

As Mark mentioned, you can move screen close to vehicle to hold some focus (you can always defocus the RP). I tended to do the opposite and get the screen as far away as possible, as we were moving camera outside of vehicle to slide from front seats to back, and was trying to get as much "perspective shift" between the car and the distant background to be "real".

As Tom asks, trying to wrap a move from front window to back would be challenging and would require larger screen(s) - I've never done it and was pretty much filling the frame with the screens just on more basic setups. Also our 2nd projector was used to project window reflections upwards into a white bounce, which helps sell it. Take care to sync thereflections with the BG's, and to cheat from that when needed (some window reflections better than nothing for too long)

Don't underestimate how much space you'll want versus how much you'll
need. It really does help to get big sources far away, and have room to tease it off the RP screens.

I also moved the sunlight just a bit on an old lighting crane our lot best-boy had found - movement as the car passed through curvy mountain roads. If I had more guts I would've let an a-pillar shadow go over the actor's face as in real life. Initially I thought it might look fake to move the sun, but done subtly it really helps.

I learned this simple trick and lots more from watching Rodney Charters on "24" - he's a master at this RP stuff. I've only scratched the surface. For night I'd motivate from the BG, and likely use a spinning menace-arm for a streetlight and some judicious use of headlights/brakelights as I'd do on poor-man's process, but less of it as the BG's selling it.

I also was glad that we shook the cameras realistically. IMHO, if there's not a bit of bumping its a tougher sell. "The Game" had some amazing RP shots, and many wider angles and not bumpy... just as a reference. If I recall correctly from the AC article, they shot some (if not all) of the BG plates with same lenses/focus - really matched it perfectly - check it out.

When you take care of covering your bases, its amazing how well it works, and frankly the "real" tow shots from an insert vehicle end up looking far more fake than RP ! Not to overlook: best stock BG plates were from Primary Colors - the quality and options in BG plates makes all the difference.

Mark Doering-Powell
Los Angeles based DP

> I want to shoot a car scene via rear screen projection.

As usual, it all depends more info please...

What format are you shooting, film, tape, HD?
Are you delivering in film or tape? (big screen, little screen?)

Things that work for one format may not work for another for a variety of reasons.

Have you shot your background plates yet?

Mark Weingartner
LA based VFX DP/Supervisor

>>I'm shooting HD (1280x720) and the final most likely won't go to film. >>Haven't shot plates yet.

I have not researched this for a while, so this may not be the absolute most up-to-date info, but conceptually it should be somewhat useful.

I will assume for the moment that you will shoot your background plates electronically and not on film, so figuring that you will project electronically, you have two basic technology choices. The best color rendition is currently with DLP projectors, which use micro-mirrors to reflect light from a Xenon lamphouse. Disadvantages with DLP projectors include the need to sync to the camera to avoid artifacts from the refresh and the possibility in some situations of additional artifacting having to do with the frequency driving the mirrors in some mid-tones.

Slightly less fabulous with regard to color rendition, ( but prevalent in this use) are high powered LCD projectors. They tend to use some sort of metal halide (or sometimes pairs of metal halide) lamps and as such, their color spectrum is not quite as complete as DLP's, but in most cases this is not a problem. One GREAT advantage is no need for sync cables or genlock since the LCD's persist until told to change each frame... no blanking. If needed, multiple projectors can be stacked, electronically aligned to each other, and driven with the same material to double or .triple the output until you run out of money.

In terms of screen materials, the two big players are Da-lite and Stewart... traditionally for motion picture rear projection we tended to use stewart, but both make quality product. screens come in different gains, the higher gain screens transmitting more light but being much more prone to hot-spotting... the lower gain screens having more diffuser material in them and a texture built into them that renders their brightness more uniform from center to edge and from straight-on viewing to off-axis viewing. Rephotography builds in contrast... any hotspotting is more noticeable in RP work than to the eye, so go for low gain screens designed for wide angles of view.

In spite of the short projection throw distances claimed by the outfits that rent RP projectors and screens for convention/trade show/ rock concert work, you can vastly improve your hotspotting problems by putting the projector as far away from the screen and using a long projection lens rather than having it close... the more acute the angle between the rays hitting the ctr and edges of the rp frame, the less hot-spotting... and no, you do not lose nearly as much light output adding all that air between the projector and the screen as you gain in overall flatness of field.

These projectors are native daylight balanced and are most efficient at daylight.... they can be partially re-balanced electronically, but using daylight lighting on stage and balancing for daylight or partially correcting the projector with filters can both help out color balance issues.

In principle, you want the screen as close to the car as possible in order to keep focus from the actors to the background, but you want the screen far enough away that you can control the spill falling on it from the sources with which you are lighting the car. I have worked with screens as big as 36 feet wide, so setting a screen that will work for a camera moving from a front shot to a side shot is possible.... but you had better do your math and figure out how to shoot the plate for that shot... you can't fix perspective that you have built into the plate.

Light spill on the front of the screen should be avoided, and the lower gain screens which have more white pigment in them will show the spill worse than higher gain screens... but light spill on the screen from behind MUST be KILLED.... ALL OF IT... exit signs, work lights, grid lights, all of it. In doing RP, I would always build a black Duvetyne tunnel down which I would project, including Duvetyne on the floor, to reduce spill to a minimum.

As far as vendors in NY (if that is where you are shooting) I have not recommendations, but test test test...and remember that doubling screen size quarters light brightness for a given projector.

I happen to love RP... or "in-camera compositing" as we can call it....but it takes discipline and accuracy to get it right. Of course bad digital post comps with poorly shot or inappropriate plates suck too, but a bit more fudging is available in post.

Zoran Peresic's book on Special Effects Cinematography is a good primer on plate-shooting issues.... likewise various editions of the American Cinematographer Manual discuss plate photography for process rephotography.

Gotta run, but this is some of the starting stuff to think about.

Mark Weingartner
VFX DP/Supervisor

LA based

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