Fringing

Fringing appears on the edges of objects — mostly greenish or bluish halos that look like an unclean transition. This happens because the color channels (especially chroma) are not synchronized during the keying operation. While you're isolating the green screen, a color cast remains around your subject, which matches neither the background nor the foreground color. You'll recognize it immediately: the talent in front of the new background looks like they have a colored halo.

The causes usually lie in the setup. Weak or uneven screen illumination leads to a grainy keying signal — the keyer cannot precisely define the edge and overcorrects in the color channels. Poor camera focus also exacerbates this: blurry edges are treated aggressively by the keying process. Another classic: an incorrectly calibrated chroma key mask or too much despill aggression. If you're too aggressive when removing green screen reflections, you erode the edge information, and colorful artifacts are created.

Practically, you combat fringing on multiple levels. On set: illuminate uniformly, check focus, maintain distance from the screen. In editing or in the VFX suite, there are tools like chroma-subsampling-aware keyers (which treat the U/V channel separately), edge sharpening after keying, or edge-light-wrapping — this creates soft halos around the edge that match the final background. Some DaVinci grades or Nuke keyers have dedicated fringing reduction modules that specifically reprocess the color edges without destroying alpha integrity.

The clean workflow: key neutrally first, then keep spill suppression minimal, then subtly refine in color correction. Never aggressively correct color during keying itself — that's post-production. Also, pay attention to bit depth: 8-bit material is less forgiving of keying errors than 10 or 12-bit. For VFX-heavy shots with a lot of movement and complex edge geometry, you often need roto support as a fallback.