Bright Ideas (page 2)
Beyond The Basics
If your editing suite has more sophisticated video diagnostic tools like a waveform monitor (WFM), you can perform adjustments that are even more accurate. Figure 3 shows the screen of a waveform monitor reading the values of a video signal. If you feed those same split field bars to the WFM, the pluge would fall precisely at the 80% line.
We've also highlighted the 100 IRE line. If the brightness value of any part of your signal goes over 100 IRE, it's said to be illegal in broadcast video terms. And if you're hoping to get your work broadcast locally or nationally, illegal video is a very bad thing. Digital video cameras can never go over 100 IRE. Most editing programs have brightness limiting or clamping tools so that you can get your brightness levels into the correct range for broadcast.
It's also valuable to check tapes you shoot with a waveform monitor. Notice how balanced and well distributed your signals look across the face of the waveform monitor. Large patches of deep shadow will show up as troughs on a WFM. Bright areas will spike higher. Looking at the display, you can see how well-balanced your shots are with respect to brightness and whether you're capturing good mid-range tones, which is often an objective sign that a scene has been well-lit and has good visual depth.
Take Control!
Now that we've seen how the measurement tools work, let's turn our attention to the post-production brightness controls in your editing software and examine how to use them to for video problem solving.
As you know, brightness raises or lowers the overall brightness level of the entire shot. Contrast, on the other hand, defines the difference between the brightest and darkest parts of a scene. A low contrast scene is all gray, while a high contrast scene has dark blacks and light whites.
Another common brightness manipulation tool, gamma correction, is available in many video editors. Roughly speaking, gamma focuses on enhancing or limiting the brightness of the mid-tones of a picture, a range that contains much of the pictures visual depth.
There's a Limit!
Playing with the brightness tools in your editor is easy and the results are simple to interpret and watch in real time. When you work with clips with big brightness or contrast problems and apply brightness, contrast and gamma filter adjustments, improvements are obvious. And if you've properly set up your monitor with the pluge, you can trust your eyes to give you an accurate reading of the results.
Using just these controls, you can correct many of the problems of over or under exposed shots in post. Many, but not all. That's because in order to manipulate data, you need to have the data to begin with. Remember how we said that digital video cannot go above 100 IRE? You won't be able to lower the brightness of anything at 100 IRE and recover any detail at all. Likewise, 0 IRE (or 7.5 IRE) blacks will show no detail whatsoever no matter how high you drag the brightness slider.
There will never be a control on any camera or in any magical editing suite that will be a real substitute for learning to shoot good pictures in the first place.
Happy Editing!
Contributing Editor Bill Davis owns and operates a video production company in Arizona.
SIDEBAR: So What is a Radio Picture?
The IRE standard came out of the Institute of Radio Engineers: this stuff was figured out when there was no TV, hence no Institute of Television Engineers or even any television engineers. Nowadays, the IRE has been replaced by the IEEE (say “Eye-triple-E”) units, which means they’re established standards of the Institute for Electrical and Electronic Engineers. Everyone still talks about IRE anyhow. Now if we could just figure out what an RKO Radio Picture was…
