OT: Photographing DLP projectors

jeremyk wrote on 7/13/2009, 9:47 AM
I'm shooting an opera production that has a lot of background projections from DLP projectors, and the color balance that the camera sees is noticeably bluer than what the eye sees.

Does anyone have experience with this? Is it ultraviolet light from the projectors? Would a skylight filter on the camera help? Should I shoot with daylight balance and adjust in post?




rs170a wrote on 7/13/2009, 10:00 AM
As I recall, those bulbs have a colour temp of 5600 (daylight) or higher so you need to make the difficult choice of ignoring it or fixing it in post (shudder!!).

musicvid10 wrote on 7/13/2009, 10:07 AM
Standard stage lighting is typically 3200-3600K.

Problem is, those things are often able to project up to 9300K, so the solution is to catch the guy in the booth when he is having a good moment, and ask him to change the color temperature in the projector's settings. You probably will not be able to get it down to 3200K, but the warmest color temp available should be quite a bit better than what you have now.

Correcting in post, you would probably have to set the stage quite warm and the screen cold in order to achieve any kind of a balance.
apit34356 wrote on 7/13/2009, 10:20 AM
The underlaying problem with lowering the projector's K is that it will darken the stage, which means an increase in brightness maybe required to make up the "loss" K, possibility outside the bulbs range. But maybe it will work! ;-)
musicvid10 wrote on 7/13/2009, 10:32 AM
Right you are, apit.

Another problem of doing this, essentially with the same effect that you mentioned, is that lowering the projector's color temperature decreases the perceived contrast between the projected image and the ambient "wash" from the stage lighting, increasing its (undesirable) effects and muddying the image. For that reason alone, you may never get the lighting designer to go along with such a plan.

It's amazing the range of color temperatures the human brain is able to adapt to in life, but how sensitive we are to those same differences when they are recorded on film, photographs, or video ("But the bride didn't "look" green at the reception!")
rs170a wrote on 7/13/2009, 11:25 AM
Another (albeit slim) chance is to see if you can put a piece of colour correction gel in front of the projector lens.
Other than getting permission to do this, the biggest hassles would be finding the right one to use and seeing how much of a light loss you'd get by doing this.

jeremyk wrote on 7/13/2009, 12:03 PM
Thanks, everybody!

Actually, the projections are mine as well, so I have complete control over the situation.

The odd thing is that looking at the scene directly, the color balance between projections and stage lighting is fine. (I'm using a warm color temperature setting on the projectors.) It's just in the camera's viewfinder that the projections are blueish. The recording is mainly for archival purposes, so it's not totally tragic if I can't get the projections accurately rendered, but I can't help wondering if there's something odd going on with the camera vs. the human eye.

I observed a possibly related problem shooting a show a few years ago that had quite a bit of purple in it. The human eye sees purple at the far blue end of the spectrum because the eye's red sensors are still active as the blue sensors reach the edge of their sensitivity. I would look at the set and see purple, but the camera was seeing only blue.
musicvid10 wrote on 7/13/2009, 12:29 PM
Doubt it will help much in this situation, but you might also try a clear UV filter over the lens. They're cheap enough that it's worth a try. However, they are less effective in reflected light situations such as yours.

. . . or, if you can find something that will fit, a clear UV filter over the projector lens. That might be even more effective.
farss wrote on 7/13/2009, 2:04 PM
"I can't help wondering if there's something odd going on with the camera vs. the human eye."

The video system cannot represent all the colors that the eye can see. Out of gamut colors end up as colors that the system can represent. To compound the problem LCDs are generally unable to reproduce all the colors that the video system can represent.

Chienworks wrote on 7/13/2009, 2:23 PM
"It's amazing the range of color temperatures the human brain is able to adapt to in life, but how sensitive we are to those same differences when they are recorded on film, photographs, or video ("But the bride didn't "look" green at the reception!")"

Very true. Photograph a typical living room scene under incandescent lights, showing the television in the picture. While you're sitting in the room you never notice how much bluer the TV is than the room lights. In the photograph the TV will look painted blue and the people will look sunburned.

I notice analogous issues with audio too. When i'm in a noisy situation i can usually make out what people are saying without too much trouble. Listen to a recording made in that same situation and it's often impossible to discern the words. Consider all the posts in these forums about removing wind noise. The brain is able to use other cues when experiencing the situation live in order to help filter. When listening to the recording all those cues are gone and the brain can't perform the job as well anymore. Video has a similar problem in that it doesn't reproduce all the information necessary for the brain to interpret it correctly.

The other issue i've always had to deal with is dynamics. The typical stage show i record has a 30 to 40dB range between the spoken lines and the big chorus numbers. People sitting in the audience absorb the difference without trouble. Play back an unmodified recording in someone's living room, and they'll be leaning towards the speakers struggling to hear the lines and covering their ears and cringing during the music. I usually have to compress that 40dB range down to about 10dB before people are comfortable with it. In a live performance a 10dB range would seem very flat and uninteresting.
Woodenmike wrote on 7/13/2009, 4:03 PM
stage lighting and projections are always at odds for all the reasons mentioned. doing lighting for ballet and now incorporating projections in much of it, i have found that the best solution albeit not perfect, is to color balance with a warm card in an un-gelled down pool in front of a bright portion of the projection to get some of the ambient light from that onto the balance card, similar to balancing for daylight from a window in a tungston lit scene. both color temps will shift towards the between area, but it will be closer to one another than balancing for just one source.
rs170a wrote on 7/13/2009, 5:07 PM
Woodenmike, the reason I don't like doing that is that it throws off the colour scheme that the lighting designer came up with.
This becomes apparent when you're watching it later on video.
If this isn't important, then go ahead and do it but I personally balance for the on-stage lights only.
For the same reason, if I have an indoor scene lit with tungsten, I leave my white balance at 3200 preset.
If some daylight creeps in (like a window) and I can't gel it, I'll just leave it blue.
I've found that the audience is more concerned with the main action and will tolerate blue windows.

musicvid10 wrote on 7/14/2009, 6:23 AM
Both good comments.
I think the key word here is "intrusiveness."

A bit of daylight coming in a window (what kind of theater do you work in??) is going to be less objectionable, and setting the WB warmer won't do much to enhance the overall lighting.

However, a projected sequence or subjects under a daylight-balanced follow spot (we had a previous discussion about this) are going to look bad, because they are the center of attention, even if only for a scene or two. A compromise WB is one approach, but the differences are so extreme in some cases as to make both types of scenes look bad.

I think if needed good balance for a projected sequence or cold-spotlit scene, I would set up a third camera, if only a DV, WB it for the cold-lit scenes, and splice in that footage in post.

Also, the projectors make a big difference. One theater we used a lot this decade used some high-priced Eiki's and the balance always looked fine on the video. Don't know what settings / tricks the lighting designer used to achieve this, because I never had a question about it. Now, about follow spots, that's a different story entirely . . .