animation
Onion skinning
Dragonframe / Timing, spacing and arcs in stop-motion animation
Definition
Onion skinning is the capture-software aid that lays one or more previously shot frames translucently over the camera's live view. It lets a stop-motion animator see where the puppet was a moment ago while posing it for the next frame. It compares pictures, not physical positions: it shows the size and direction of a move as seen from the lens, which makes it the animator's main on-screen check on spacing, drift and registration. It works the same way whichever stop-motion sub-type is being shot, whether puppet, clay, cutout or object animation.
Overview
The animator's basic problem in stop motion is that the previous pose no longer exists. By the time the next frame is being built, the puppet has already been moved, and the only record of where it was is a picture. Capture software keeps that picture close at hand. Dragonframe records two parallel sequences as a scene is shot: low-resolution video-assist frames grabbed from the camera's live feed, which are used to refine the animation, and full-quality stills for the finished film. Onion skinning works on the first of these. It dissolves stored frames into the live feed, so the new pose is built against the ghost of the old one rather than against memory.
Dragonframe controls this with a single opacity slider that works in two directions. On the READY TO CAPTURE frame, moving it right blends the last shot frame over the live view, and pushing it all the way shows only the previous frame. Stepping back to any earlier frame and moving the slider left dissolves that frame over the live view instead, which is how an animator checks a pose against a key several frames back. A second slider layers up to five frames over the live view at once, and that is the view that shows an arc as a trail of positions rather than as a single step. The ONIONSKIN keys on the Dragonframe keypad nudge the opacity in small increments, so none of this needs a trip back to the computer. The 2027.01 development builds add an assignable Onionskin Toggle hotkey (build 18840). That is development-branch software, not yet a stable release.
The transfer modes are where onion skinning becomes a measuring tool rather than a ghost image. Difference mode turns everything identical between the two images black and shows what has changed in grey or white. The manual's own example is a ball nudged slightly to the right, which leaves white wherever it moved. Darks prominent is meant for dark subjects on light grounds, such as a black line drawing on white paper, and Lights prominent for a bright object on a dark set. The manual presents Difference mode as a way to judge the move. The same view also exposes anything that changed without being meant to, such as a set piece that was brushed or a prop that slipped, and it catches them before the frame is committed.
Blending is not the only way to compare. Dragonframe's LIVE TOGGLE key flips between the live view and the stored frame on each press, and AUTO-TOGGLE flips between them continuously at an adjustable rate. A blend shows two positions at once. A flip shows the change as movement, and a small drift that is hard to see in a blend often shows up clearly as a jump. Good practice uses both. The blend is for placing the puppet, and the flip and playback confirm the result.
Onion skinning has two built-in limits, and both are worth knowing. First, it compares flat pictures from the lens's point of view, so a move toward or away from the camera barely registers. That blind spot is why the surface gauge still sits beside the monitor on a professional stage. Second, it runs on video-assist frames, which are lower in quality than the capture. Dragonframe's HIGH-RES key switches playback to proxies of the full-resolution frames, and that is the better view for judging a finished move. The onion skin tells the animator where the puppet is. Only playback tells them whether the move works.
The tool is not limited to the animator's own previous frames. On *The Secret Agent* (2025), animator Rosanne Janssens at Holy Motion animated a 30-centimetre "hairy leg" puppet against green screen in Dragonframe for three weeks, using onion skinning with the live-action plates underneath to follow a camera move shot earlier on 30 metres of ground-level track in Brazil (Cartoon Brew, 4 March 2026). The picture being compared against is then someone else's footage rather than the last pose. The check is the same, though: does the new pose sit where the plate needs it? That plate-under-live-view setup is described under dragonframe-guide-layers.
Workflow
- Press LIVE to go to the live view (the READY TO CAPTURE frame).
- Press ONIONSKIN RIGHT (+) on the keypad, or drag the opacity slider right, until the last shot frame shows faintly over the live feed.
- Pose the puppet against that ghost, reading the gap between the old and new positions as the spacing of the move.
- For arcs and longer moves, select the Onionskin tool in the Animation palette and drag the frames slider right to layer up to five previous frames.
- To check against an earlier key pose, step to that frame and press ONIONSKIN LEFT (-) to dissolve it over the live view.
- Before shooting, switch the Onion Skin Mode to Difference to confirm that only the parts you meant to move have changed.
- Flip with LIVE TOGGLE or AUTO-TOGGLE, and check moves toward or away from the lens with a surface gauge, because the onion skin cannot see depth.
- Press SHOOT, then review the sequence with playback, using HIGH-RES to judge it on proxies of the full-resolution frames.