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Video scopes make these problems even clearer. Since all major video editing software has video scopes built-in, we can easily check levels on set before beginning production for the day. There are two relevant scopes: • • Waveform Monitor, which measures gray-scale (light and dark) values Vectorscope, which measures color values We use the two scopes in tandem to evaluate an image, because, for a key to work, we need to be able to isolate a SPECIFIC background color from all other colors in the image. Since a “color” consists of three values: hue, saturation and gray-scale these two scopes help us make sure we have a clearly isolated color. A better way to work Compare that fi rst image with the one above: • Perfectly smooth background • Evenly lit background • And note that the actor is lit dramatically, while the background is lit evenly. This will look magnifi cent when the key is pulled, even down to individual strands of hair. Here’s the same shot, this time using the Vectorscope. Look how the colors are desaturated (close to the center) and range in value from close to gray to kinda-sorta-leaning-toward green. Maybe. There’s no clear-cut color to grab. This causes edges to tear, strands of hair will be lost, and, in general, the fi nal key will look awful. KEY RULE: The more of the actor’s body you need to see, the better your background and lighting need to be... or, plan to spend a LOT of money in post cleaning this up. Here’s the Waveform Monitor for that second image. Look how even and tightly controlled the background is - almost exactly at 45% and dead smooth. This is a near-perfect example of how to light a background. Rich color • Here’s that image displayed on the Waveform Monitor. See how the green values range from about 12% up to 50%? In fact, some of the green is darker than the performer. This huge difference in value will cause major problems in editing, because we won’t be able to isolate the talent from the background; all the colors are blending together. Here’s the same image on the Vectorscope. Look at how clearly defi ned that green is, and the color separation between the background and the talent. This is exactly what you should expect to see when monitoring your effects on set. Summary I know that production never has enough time, but when it comes to chroma-keys a few extra minutes properly setting and lighting the studio for a chroma-key shot can save bundles of time and dollars later in post. Whether you are a studio-owner or a producer, keep these rules in mind when considering a green-screen shoot. Pick facilities that can make your life easier and less stressful by giving you the room, surface and lights to make your keys look great. And don’t be afraid to record a quick test clip and load it into the editing software of your choice. Check the shot on the scopes. It is far easier to fi x lighting and set issues in production, than work around them in post. TV-BAY MAGAZINE: ISSUE 92 AUGUST 2014 | 41 TV-BAY092AUG14.indd 41 08/08/2014 15:28