Short answer: pick the tool by the shot, not by brand. Use a keyer when the footage was shot on an evenly lit green or blue screen. Use Roto Brush, or a hand-drawn mask, for a subject with a clear edge that you can refine. Try WispFX when the edges are hair, fur, smoke, glass or motion blur against a busy background and you have an NVIDIA GPU on Windows. Compare the results on your own shot before you commit.
Keyers, Roto Brush and masks are built into After Effects. WispFX is a separate panel that adds an AI alpha matte to After Effects, and an effect for DaVinci Resolve.
The approaches
| Approach | What it is good at | Where it struggles |
|---|---|---|
| Keyer (for example Keylight, built into After Effects) | Shots on an evenly lit green or blue screen, with spill control. | It needs a screen. On ordinary backgrounds there is no clean colour to key out, so hair and glass are hard. |
| Roto Brush and Refine Edge (built into After Effects) | A subject with a clear edge. Roto Brush carries a brushed selection through the shot, and Refine Edge works on the matte edge. | Fine hair and soft edges often need hand refinement. |
| Masks and manual roto (built into After Effects) | Exact shapes, frame by frame control, and any subject you can draw. | Slow on moving subjects with fine detail. Mask edges are drawn shapes, so fine hair needs many points or a separate edge method. |
| WispFX | Soft alpha for hair, fur, smoke, glass, liquid and motion blur, without a screen. Subjects are picked by clicking and tracked through the shot. | Windows with an NVIDIA GPU only. Needs 8 GB of video memory or more, a model download of about 33 to 43 GB, and render time per clip. No per-frame spline editing. Sheer fabric and glass interiors have limits. |
Which to use for which shot
| Shot | Start with | Why |
|---|---|---|
| Evenly lit green or blue screen | A keyer | The screen gives the keyer a clean colour to work from. |
| Hard-edged subject, short shot, few frames | Roto Brush or a mask | Quick to set up, and the edge is easy to refine by hand. |
| Hair, fur or smoke on a busy background, no screen | WispFX, then compare with Roto Brush | The model predicts soft alpha for these edges. |
| Glass, liquid or motion blur | WispFX, checked in the Cutout view | Semi-transparency is kept. Glass interiors keep faint alpha. |
| A shape that must follow an exact line, frame by frame | Masks | WispFX has no per-frame spline editing. |
| No NVIDIA GPU, or a Mac | Built-in After Effects tools | WispFX runs on Windows with an NVIDIA GPU only. |
How to compare on your shot
- Choose three hard frames: hair against a bright background, a frame of fast motion blur, and the frame with the fastest movement.
- Build each candidate in the same comp: the keyer or Roto Brush result, and the WispFX matte.
- Judge them over the new background you will use, in the Alpha and Cutout views, not on black.
- Scrub the whole shot, not only the three frames. Flicker shows up across frames.
- Choose the result with fewer holes, cleaner edges and less flicker, counting the time each one takes you.
What has and has not been measured
The examples on this site are WispFX output only. We have not published a head-to-head benchmark against Roto Brush, keyers or other tools. WispFX render times are measured on an RTX 4090 with After Effects open. Roto Brush and keyer times depend on your shot and machine, and we have not benchmarked them.
Limits of WispFX
- Very sheer fabric can come out more transparent than it should.
- Glass interiors keep faint alpha and the refracted background.
- No per-frame spline editing. Use masks for exact shapes.
- Tested on Windows with an NVIDIA GPU only. No Mac build at launch.