Animation technique: multiple frames shown semi-transparently overlaid in the editor—tracks motion lines precisely. Standard in mocap and stop-motion pipelines.
You're sitting in front of your animation timeline and need clarity on a character's motion path between two keyframes — that's exactly where Onion Skinning comes in. The technique overlays multiple consecutive frames semi-transparently in your editor window, allowing you to grasp the direction and speed of movement at a glance. Instead of clicking through individual positions one after another, you see them all simultaneously — that's the core idea.
The practical benefit becomes immediately clear when working with motion capture: The raw data from the mocap system is often noisy, and individual frames don't show you whether a hand is actually moving smoothly away from the body or jumping. With Onion Skinning, you layer five, ten, or even twenty frames on top of each other and immediately recognize where the curve breaks. You see artifacts, unnatural accelerations, missing intermediate positions — all in one view. This saves you hours debugging mocap data.
It's also indispensable in stop-motion workflows. When you photograph a puppet frame by frame, you need to know what the position of the last three shots looked like to place the next one. Here, you often overlay the current and previous frames transparently — the DoP or animator sees on the monitor whether the movement remains continuous. Many professionals set the opacity so that the current frame is visible at 100% and the last three at 20-30%. This creates a "ghost image" of the movement.
Most professional tools offer Onion Skinning as a standard feature: In Maya, Blender, and Nuke, you can activate it with a few clicks and control the number of preceding and succeeding frames. In compositing, you use it to precisely align reconstructions or drawn effects with existing motion — for example, when you need to track a CG character frame-accurately over a live-action performance. The transparency can be controlled granularly, often with color coding: frames before the current one in one color, and after in another. The eye then immediately grasps the temporal direction of the movement.