One of the by-products of video from HDSLR is the banding artifacts that can result from the rolling shutter used to capture the video image.
When shooting under fluorescent light (very common in commercial locations) the flickering of the light source can create colored bands across your image which move across teh frame and pretty much ruin your shot.
Simplest fix is to make sure you're shooting at the correct shutterspeed. For the purposes of keeping motion-blur and strobing under controll, the 180-degree shutter rule dictates the shutterspeed be set to 2x the framerate. A 24p framerate would require a shutterspeed of 1/48" (functionally 1/50"). Only problem here is this framerate is too slow to avoid banding.
In the US fluorescent bulbs have a frequency (flicker) of 60Hz so setting your shutterspeed in multiples of 60 (e.g. 1/60", 1/120", etc.) will negate the banding. Same rule applies for Euro countries where the bulbs are 50Hz. Here's a quick cheat sheet:
- IF: Framerate = 24p, 30p or 60i
- THEN: Shutterspeed = 1/60"
- IF: Framerate = 60p
- THEN: Shutterspeed = 1/120"
- IF: Framerate = 25p or 50i
- THEN: Shutterspeed = 1/50"
- IF: Framerate = 50p
- THEN: Shutterspeed = 1/100"
BUT MY FOOTAGE ALREADY HAS BANDING, WHAT NOW?
This can be a tricky fix to make in post -- but not impossible. All it takes is a little time with a Color-Correction Filter and tweaking some of its masking properties.
Here's a great guide from DSLR Video Shooter walking through the fix in FCP7: