How to set the correct exposure using Zebra
If your video camera has a Zebra function then it’s handy to understand a little about it. It’s a way of setting the correct exposure.
The slanted striped pattern (hence, Zebra) that you see is set to overlay on areas of the viewfinder/LCD image that are of particular brightness – commonly somewhere between a value of 70 and 80 IRE* of the whitest white that’s possible to record. There are two basic types of zebra display, 100 IRE and another that’s often adjustable, 70-80 IRE.
Notice that this electronically generated striping plays on different parts of the image as you close down or open up the iris. This is because as you lighten or darken the image, elements in the scene fall into this 70-80 IRE value. Caucasian skin highlights occur at about 80 IRE, so you should adjust the iris to display the zebra pattern on the highlighted areas of the subject’s face. Just for practice, try this:
Frame the camera on someone as if you were shooting a portrait. Making sure that the Zebra is set to 70 IRE (or “percent” as it’s sometimes written), turn the iris adjustment so that the zebra striping is active all over the face. Now close down the iris so that the striping starts to disappear.
Leaving a stripe or two on a highlight area – a cheekbone or top of the forehead is usually the best setting. The skin tone is now correctly exposed and this ensures that everything else in the scene is also correctly exposed.
Another useful way to use Zebra function is to use it as an exposure meter. With your camera set to Auto mode, frame the camera at the scene to be recorded and note on which parts of the scene the Zebra stripes are active. Switch the camera to Manual operation and adjust the iris control so that the Zebra stripes overlay in the same place that they were in Auto.
This way, your manual exposure setting is going to be at least in the right zone. I usually then close down another stop to give the picture a little more saturation. Remember, the slanted striped pattern is not recorded on the tape.
If your camera doesn’t have a Zebra exposure control but you’d like to have manual control of the iris, then this is what I suggest: with the camera set to Auto mode, frame it at the scene to be recorded, make a note of what the overall brightness level looks like in the viewfinder.
Switch to Manual operation and adjust the iris so that the image brightness matches what you saw in Auto mode. In it’s basic form you’ve used the Auto mode as an exposure meter.
© 2013 Pieter de Vries ACS