In order for an animation to appear smooth it must be played at at least 10 frames per second (higher frame rates appear even smoother). Creating each frame manually can therefore be a time consuming process. In the days of traditional hand drawn animation, skilled animators would draw every 4th frame (called key frames) and less skilled animators, called inbetweeners, would then fill in the missing inbetween frames to create smooth movement. The process became known as inbetweening or just tweening. Now in the era of computers that process can be performed automatically.
An example of Inbetweening. The 3 key frames are created by the animator (shown with an outline)
and the inbetween frames are created automatically by the computer when playing the animation.
The final animated sequence is shown on the right.
In Pivot Animator you can create key frames in the timeline and then select how many inbetween frames to create between each pair of frames. This means less time to create your animation and results in smoother movement. Everything about a frame will be inbetweened where possible, from the pose and colour of each figure to the position of the virtual camera. It also enables the smooth fading transition of backgrounds.