Inbetweening is the process of creating transitional frames between two separate objects in order to show the appearance of movement and evolution of the first object into the second object. It is a common technique used in many types of animation. The frames between the key frames (the first and last frames of the animation) are called “inbetweens” and they help make the illusion of fluid motion.

Sophisticated animation software have complex algorithms that identify the key frames in an image and define how the transition goes, creating the inbetweens for the tweening process and completing the animation. This is done by interpolating graphics parameters or data. On the other hand, all of this can be done manually, which is what animators often do as they need more control of the process than what an automatic algorithm can afford. Some animation software that automate the inbetweening process still allow manual means of editing each inbetween frame so that the animator can be sure that the movement is fluid and lifelike or whatever demand is.