Onion skinning is a feature in animation software that displays semi-transparent ghost images of frames preceding and following the current frame alongside the frame being drawn or edited, allowing the animator to see where a subject was and where it will be as they work on the current position. The term comes from the translucent onion skin paper used in traditional hand-drawn animation to achieve the same effect by layering physical sheets.

The technique is fundamental to the frame-by-frame animation workflow because it allows animators to control the spacing and timing of motion with precision. By seeing the previous frame as a ghost behind the current drawing, an animator can judge exactly how far to move a subject to produce the intended speed and arc of movement. By also seeing the next frame's ghost (in tools that support bidirectional onion skinning), the animator can ensure the current frame sits correctly in the middle of the intended motion arc. The number of frames shown as ghosts and their opacity are typically adjustable, with more frames visible for complex motion arcs and fewer for simple movements. Onion skinning is used in all forms of frame-by-frame digital animation, from mobile apps to professional 2D animation software.

For creators working with AI generation to produce frame-by-frame animated content or to refine generated motion, understanding onion skinning helps when transitioning between AI-generated starting material and manual refinement. While AI generation itself does not use onion skinning, the animation software used to refine, extend, or retouch generated frames relies on it as a core navigation tool for understanding movement across time.