Filming an LCD projection

Micah Fernandez · April 22, 2009

Hi all!

I'll be shooting a music video in a large auditorium with a stage. The talent will be performing on stage to a darkened auditorium, and the director wants a projection of previously shot footage to be playing in the background, with the image sometimes directly projected on her.

I figure that I'll need to boost or cut any additional lighting I have to accommodate the LCD projector's brightness, but since it's my first time to be filming a digital projection, I was wondering if there were any other issues I need to guard against, such as the projected image's color on camera, flicker or scan lines, and the like. Any tips/advice is appreciated. Thanks!

Chris Keth · April 22, 2009

Hi all!

I'll be shooting a music video in a large auditorium with a stage. The talent will be performing on stage to a darkened auditorium, and the director wants a projection of previously shot footage to be playing in the background, with the image sometimes directly projected on her.

I figure that I'll need to boost or cut any additional lighting I have to accommodate the LCD projector's brightness, but since it's my first time to be filming a digital projection, I was wondering if there were any other issues I need to guard against, such as the projected image's color on camera, flicker or scan lines, and the like. Any tips/advice is appreciated. Thanks!

Find out what projector will be used and, if needed, get a bigger one. I've done this a couple of times and both times we had to wait on a brighter projector.

There aren't scan lines and the color is easy to tweak in the projector settings. You will, as you suspect, have to watch your lighting so you don't entirely washout the projected image.

Saul Rodgar · April 22, 2009

There aren't scan lines and the color is easy to tweak in the projector settings. You will, as you suspect, have to watch your lighting so you don't entirely washout the projected image.

Indeed. There are, however, some LDC projectors that show pulsating colors in parts of the image, dunno why or precisely which kind, but I have encountered them before. I have tried changing the scan rate on the camera and the shutter speed, all to little avail. It is not as noticeable as the scan lines but it sometimes is enough of a distraction to watch out for.

Also, most (if not all) LDC projectors have daylight balanced bulbs in them, so it there are any other (tungsten) lights pointed at where you are filming, you may have to compensate for that.

This, as in pretty much every filming situation, requires some pre-production to go smoothly, so test away.

Chris Bowman · April 23, 2009

Indeed. There are, however, some LDC projectors that show pulsating colors in parts of the image, dunno why or precisely which kind, but I have encountered them before. I have tried changing the scan rate on the camera and the shutter speed, all to little avail. It is not as noticeable as the scan lines but it sometimes is enough of a distraction to watch out for.

Also, most (if not all) LDC projectors have daylight balanced bulbs in them, so it there are any other (tungsten) lights pointed at where you are filming, you may have to compensate for that.

This, as in pretty much every filming situation, requires some pre-production to go smoothly, so test away.

Those pulsating colors are from the rotating color wheel on projectors that are not 3-chip designs. The wheel spins to filter the single chip image through each of the primary colors, and usually a clear section to enhance brightness, for every frame of video. You may or may not be able to adjust the shutter speed to match the color wheel strobe, but if your camera can do clearscan that may help. The other option is to shoot 30p or 24p (assuming you can) rather than 60i. The longer exposure should give enough image persistence to overcome the color switches.

Another important consideration is that many LCDs and EFVs do not refresh fast enough to reveal if the color pulses are occurring. Make sure you use a color CRT monitor to check the projector for color pulses, as the LCD and EFV may show a perfectly good picture, but you could still wind up with rainbow-vision in post.

Micah Fernandez · April 30, 2009

Thanks to all who replied. I was able to go into the shoot better informed and prepared, and as a result the projector was the least of my worries. :)

Marc Alucard · April 30, 2009

If the projector has a color wheel it is a DLP not a LCD.

Chris Bowman · April 30, 2009

If the projector has a color wheel it is a DLP not a LCD.

You're right, I should have specified. I assumed Saul was talking about DLP rainbow, since it is similar to what he described, and he said he wasn't sure what kind of projectors do it. Too often I've heard people use LCD as a generic term for any video projector, regardless of what the actual technology used is. Sometimes I forget that there are some people who actually know and care about the difference other than me. :blink:

Keith Walters · May 1, 2009

You're right, I should have specified. I assumed Saul was talking about DLP rainbow, since it is similar to what he described, and he said he wasn't sure what kind of projectors do it. Too often I've heard people use LCD as a generic term for any video projector, regardless of what the actual technology used is. Sometimes I forget that there are some people who actually know and care about the difference other than me. :blink:

If you can get access to the projector or TV or whatever beforehand, any cheap Handycam type camcorder will soon tell you if it is going to have strobing or pulsation problems, (although there are a few rare exceptions). But generally if you get a clean picture on the camcorder chances are it will be OK on the film. Somewhere I have a little box I made up with a motor that drives a cardboard shutter to simulate looking through a camera viewfinder, when people used to keep asking about strobing on Plasma screens. The answer was then, usually they don't, but a few do.

As a general rule, most current model LCD screens and projectors don't produce any sort of strobing, generally behaving like a colour transprency backlit by a flicker-free fluorescent lamp.

However the latest LCD screens use white LED backlighting which is dynamically brightness controlled to improve the contrast range. These use pulse-width modulation of the LEDs so this might introduce new problems, so beware and Test test test!

There are also new video projectors in the pipeline that will use high-power LEDs for the projector lamp, so the same thing could occur there.

Dan Goulder · May 1, 2009

On a parallel topc: What's the best (or close) method for software uprez from SD to HD? Can the results compare with hardware devices such as the Terranex, etc., or will they be noticeably inferior? (I believe the Terranex does line doubling, and don't know for sure if this can be suitably matched in software only.)

Question #2: If one were to film the results off an HD lcd monitor, is there a typical color temperature coming off these monitors (and what would that be), or would it vary depending upon the material itself, which is a combination of daylight and nighttime footage?

(just experimenting)

Thanks.