Color correction filter for video projector

Has anyone tried attaching a color correction filter to the lens of a video projector to match tungsten?

One one shoot, I had the cooperation of an AV support person at the college where I was video recording. The particular projector did have a color temperature and brightness control, so I was able to pretty closely match the exposure and color temperature for the presenter and presentation, but this is the rare exception. I did learn that the lumen output is higher on the blue end of the LED or DLP used (not sure which), which is why a highre color temperature is often preferred.

At least for portable presentation projector on a table, stand, or cart, I was thinking something like a matte box on a plywood base,upon which I could place the projector with an inch or so gap to the filter holder.

This is something you should only set in the menus of the projector. If that doesn't work out then the footage itself needs more calibrated color grading.

Noah

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Noah,

I don't want any post production work. I want to match as close as possible the color temperature of the projector to the color temperature of the room. I suppose another solution would be HMI lights or color correction gels on all the lamps, but it seems a lot easier to correct the projector with filters when there is no menu option to change the color temperature toward tungsten.

Oh! I think I get it. Tell me if this is what you mean: You're shooting in a space that's lit with tungsten lights, but there's a projector in the room that's putting out cooler light? So if you balance for the screen the room looks orange, but if you balance for the room the screen looks blue? Is that the quandary?

Sure, I guess you could theoretically throw a CTO of some grade in front of the projector, but that would almost certainly defocus the image on the screen too much. The better choice is to light the room differently, if that's even an option. It might not be. Are you using room lights, or windows, or bringing in your own lamps to light the room?

(As to why projectors have cooler lamps in them, it's got to do with "spikeyness" in the spectrum. Projectors work by pushing light through some sort of medium that absorbs part of the spectrum, so you need as broad a spectrum as possible to start with in order to get a good chroma response off the screen. Because metal halide lamps put out a very "spikey" spectrum, the average spectrum is really broad. The downside is that the average color temperature of the light from a metal halide lamp is around 6000K, which is much bluer than 3000-3500K tungsten light, and even perceptibly bluer than the 5500K average of daylight. Now, they do make metal halide lamps in various temperatures these days, all the way down to about 3000K, but whether you could get one in that temperature that fits your projector is an open question.)

Yeah I guess you can experiment with that but I think you'll find that the filter you try to put in front of the projector will do more harm than good as Jeff suggests. I'd suggest another projector or you just live with the best you can do menu wise and correct further in post. A projector screen is a nice geometric shape that's easily to track and correct with secondaries in Color or whatever color corrector you use.

Noah

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Color-correcting or replacing the screen might be pretty easy, but color-correcting the interactive light from the screen would be a pain in the butt.

This is getting pretty far from what you were asking about, but would it be possible to just pump green through the projector, and replace it in post with whatever's supposed to be on the screen? This is obviously not an applicable suggestion if you're shooting a live event, but if this is a setup, it might be simpler to treat the screen as a greenscreen with an assload of spill and handle it that way. Of course, that depends on what your toolchain is and what kind of video "stock" you're shooting on.

Yeah and believe me, nobody ever wants to deal with an assload of spill.

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I was assuming that there might be optically correct color correction lens filters that I could put in front of the video projector. E.g.: [www.bhphotovideo.com]

These filters are pricey, and it would be a real gamble which one to get. Also, there is no orange, just red and yellow.

I know it It isn't the best way to do things, but I did set two different white balance settings and switched from one to the other while the camera was panning toward theprojector screen. However, it didn't work because I hadn't set auto iris.

For live events with PPT, eventually I will capture a split of the DVI from the computer to projector.

I'm going to be trying out BoinxTV, a program I found with an internet search which can take multiple camera inputs and composite them with graphics, and output from the screen to AVC h.264 or even to Quicktime Broadcaster for live streamed events. Once I figure how to input the DVI split from the computer to the projector --this is my holy grail.

>>Yeah and believe me, nobody ever wants to deal with an assload of spill.<< Tsk. Leave you guys alone for five minutes, and look what happens

Blimey! I wasn't even in the room!



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It is difficult, but spill can be kept to an acceptable level. The problem is matching exposures between screen and subject. Modern video projectors are pretty bright and can overcome rook light, but it can be possible even with out a large separation between presenter and screen.

I've done it before with good results by adjusting the projectors color temperature and output. This gets it in to the ballpark. I still insert the powerpoint slides, but it makes the video much more interesting if I can capture both presenter and screen.

Not all projectors are controllable this way, however. So it is tempting to think about using filters apart from the projector to achieve similar results.

I never said it was easy.

If time permits before the shoot starts what I do is dial in a manual white balance setting to a color temp on one of the more colorful powerpoint slides with the lights dimmed down to what they will be during the shoot. I get the color close to being true by simply eyeing the color until it is close to looking real...And, of course, use one of the white balance preset positions for color balance when the lights are up at normal operating conditions.

If you have a camera that has a "Shot Transition" button (Sony's terminology) you could have the white balance and iris setting recorded into a button push and you would be completely set for your projector conditions during the shoot.

-Andrew