white balance issue
Posted 16 July 2005 - 04:06 PM
Posted 16 July 2005 - 04:53 PM
Do you have to match multiple cameras?
If not, I'm afraid this is one moment where I tend to hit the "auto" button if I'm not controlling the lighting. It's a situation where having something that looks vaguely reasonable second to second is more important than how it looks from hour to hour.
If you need to match multiple cameras, or if you have some other reason to need colour accuracy, then you need to pick something and stick to it. I don't think discharge-based intelligent lighting looks bad if you balance tungsten and let it go cold, and if you're relying on tungsten for your "main" lighting, then that's clearly the way to go. The problem I've had in the past is the need to have tungsten light look reasonable, then someone hits the talent with a discharge followspot - if your camera has shockless preset switching you could try to ride it, but again, I feel the automatic function would probably be more seamless. Yes, I know it's heresy to suggest auto anything, but in these situations where you just can't ride it manually and you need it to look reasonably seamless, it works. If you're in the position of having a vision engineer to sit on the CCU(s) and ride it that way, then fine, you'll be able to have them all go together.
If you need it to look like it does in reality, then yikes, you're in for some fun, because it's usually a futile endeavour to request this of any imaging system, let alone when you're throwing super-saturated colours at it from all areas of the visible spectrum. In my experience, big concert shoots tend to look rather like they would if I shot them on my own equipment, with visible single-channel clipping. The dichroic filters used in that kind of lighting have a very sharp pass band and they are capable of exciting just one CCD; this is the "solarisation" you're seeing. Most concert shoots look like this at least some of the time. It's fairly normal, and it can explain how some of your colours are getting bent - if you have a magenta that's red and blue, and you're clipping the red channel (atypical but possible), then it will start to look bluer as the red's already maxed out while the blue keeps coming.
If you do control the lighting, then naturally you can just tweak around to get what you want on the monitor, and hang what it looks like to the naked eye. Either way, you'll have a lot of fun trying to capture those very bright colours if that's what the director wants.
Posted 16 July 2005 - 05:11 PM
My older brother was the live sound mixer for the Gaither Homecoming video series. (well, 4 or 5 of them anyway) and I believe they employed a back stage engineer who adjusted the cameras, perhaps this is a 'vision engineer', Phil?
I occasionally work as a camera operator for corporate theater, you know, the kind with fiberoptic drape, hundreds of Source 4's, intelligent fixtures, and an LED dance floor.. "corporate theater" uh-huh.
For those events, we have white balanced all cameras to a white card on top of the LED dance floor, with several intelligent fixtures on "white" and a slew of ungelled leco's as well.
It's a wash of color and I'm not sure anyone there knows what the actual temp is.
Hope this helps,
Posted 16 July 2005 - 05:34 PM
> perhaps this is a 'vision engineer', Phil?
That's the guy.
Posted 21 July 2005 - 11:30 PM
Does anyone know what the high end productions do for color balance? We have about 9 moving lights (Martin Mac's) and the magenta colors turn "tron" blue and posterized; yellow looks really green. We tried white balancing at 5.6K, which is the color temp of the moving lights, which made the moving lights accurate, but we use dimmed source 4's, fresnels and pars that render faces really warm. I wish I could go behind the scenes at one of the HBO concerts and see what they do.
I recently did a shoot for a PBS program at a new multi million dollar high school autorium that was outfitted with like 8 of those to light the stage and speaker with only tungsten lights behind them as backlight. It was horrible lighting because it was directly overhead and was a nasty green that didn't seem to have the full color spectrem. The high schooler running the 20 foot lighting board knew nothing other than how to turn the lights on or off.
Here is some information of your lights that I found:
The MAC 700 Profile is designed for use with an OSRAM HTI 700 W/D4/75 lamp. This highly efficient double-ended short-arc source provides a color temperature of 7380 K, a color rendering index of 75.
So the key is at 7380 k a very weird color temp. A very bluish daylight. Though I understand some major awards shows are shot with HMIs (5600k daylight bakanced lights) this is not the norm. So you have three ways of working these in a TV production change all of your other lighting to daylight balance by using gels to change your tungsten to 5600k or higher, using HMIs as your key lights and fill lights for the stage. Or the last option which is to somehow adjust the color balance on each roboscan to be more redish. If it were me I would just use these lights behind the band for effects not for spotlights. Hope that helps. I imagine there is a way to make the base color temp 3200k but I am not sure. You could always fly me down there to help you out . Most of the tv work I do in a theatre under tungsten lights if that haven't used any really weird gels on the key lights for the actors that isn't to create a mood and they don't keep the lights on dim to much during the poduction then I just set my camera to 3200k preset white balance.
Posted 21 July 2005 - 11:46 PM