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May 2012

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How-to Guide to IMAG (Image Magnification)

We explore how to do IMAG from input to output.

by Jim Kumorek

 

START WITH THE SOURCE

The start of the signal chain in an IMAG system isn’t your video cameras, it’s the light coming off the objects/people you want to capture. And that light comes from the lighting fixtures used in your auditorium.

“There are two primary concerns when lighting a stage for video,” says Lighting Designer C. Andrew Dunning of Landru Design in Nashville, Tenn. “These are color and contrast. Both of these have to do with the limitations of video cameras. The human eye can deal with infinite color temperatures all at the same time, as well as deep shadows and strong highlights.” But video cameras cannot.

Color temperature refers to the color makeup of the light being used. Tungsten lighting (which is what’s in your typical theatrical lighting fixtures) tends to be rather yellow; fluorescent lighting is a bit green; arc-source lighting is rather blue. While our eyes and brains can deal with different color temperatures implicitly, video cameras need to be told what color temperature lighting they are “seeing” (or what color “white” is), so that they can accurately record the colors of the image. If you’re ever noticed photographs that look very blue or very yellow, that happens when the camera is set for the wrong color temperature. When this happens, skin tones look wrong, and the video looks terrible.

“In an ideal world, all your lighting would be of the same color temperature,” Dunning adds. “In the real world, get things as close as possible without alienating the audience. If you’re using a lot of moving lights that have arc-source lamps, color-correcting Tungsten up to the arc source color temperature would alienate the audience because it looks very cold and harsh. So, try to find a happy medium. Color correct your arc-source and video projectors down towards Tungsten, and correct the Tungsten up towards the arc source, and meet somewhere in the middle.”

Additionally, video cameras can’t deal with a lot of contrast between the shadows and highlights. “The steeper the angle of your lighting, the more shadows on facial features will be created that are hard for the camera to capture. Minimize shadows and dark spots on the stage,” Dunning says.

Other lighting considerations are the quantities of light on the platform. The lower the lighting levels, the better cameras and lenses you are going to need, and the better your camera operators need to be. Low light levels mean you need to open the iris of the camera more to get more light into the camera; the larger the iris opening, the shallower your depth of field, which can result in more dramatic on camera images.

The trade-off is that camera operators have to work harder. With the iris wide open, having your pastor move just a few feet towards or away from the camera may put them out of focus. The more light you have on stage, and smaller the iris can be, and the more leeway your pastor has to move without your needing to adjust the focus of the camera following him or her.

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Jim Kumorek is the owner of Spreading Flames Media, providing video/media production and writing services to the A/V/L, technology, architectural and hospitality industries. He has led audio, video and lighting teams in churches as both staff and a volunteer for over 10 years. He can be contacted at james@spreadingflamesmedia.com.