The Voodoo Science of Color Correction

Yesterday, I had the priviledge of spending some time with noted industry journalist & author Jan Ozer. We got into a deep discussion on color correction — how it’s still a big mystery to most of us — and eventuallly we started talking about the uses of a Waveform/Vectorscope.

waveform.jpg
The YC Waveform Scope in Premiere Pro 2.0

Waveform/Vectorcopes generally only come into play when you’re editing something for broadcast. There are legal limits on luma (brightness) and chroma (color) ranges in broadcast signals. Even if you’re not going to broadcast, if you plan to make VHS copies you’ll wind up with that “buzzing” on the audio track if your luma range is too high.

The general idea is that you need to keep your luma between 7.5 and 100 IRE. Looking at the Waveform Scope above, you can see that the luma (represented in green) is within the legal limits, while the chroma (represented in blue) is pushing below 7.5 (in Premiere Pro’s Waveform Scope, above, the green and blue lines on the right show you the luma & chroma ranges in the image). So in this example, I’d need to look at the Vectorscope to analyze my chroma and make sure everything is in the safe zone (I’ll do a posting on the Vectorscope shortly).

There’s a lack of easy-to-understand training material on this subject. One book I highly reccomend is Color Correction for Digital Video by Steve Hullfish and Jaime Fowler. It’s got a very clear explanation of how to read Waveform/Vectorscopes, and while not extensively detailed, gives you the basic knowledge you need.