Traditional animation involves a series of still images, usually painted or sketched, displayed in rapid sequence.  Because the receptors in our retina require recovery time, we are unable to distinguish each individual image in the sequence. In effect, as the previous image is replaced by a new image the previous image is still “burned” on our retinas.  Each image is blurred into the other, creating the illusion of motion.  This is called Persistence of Vision. If we didn’t experience retinal lag, we’d be able to distinguish each individual frame, destroying the illusion of motion.

With film, each image is called a frame. As a result, the rate at which each frame is displayed is measured in frames per second (fps). The movies you see at a theater display 24 frames per second.  Videotapes and television display 30 frames per second.  Film and video have fixed frame rates.  With Fireworks, you can set the frame rate.  Higher frame rates result in smoother animation, but also require more processing power. 

Key Frames and In-between Frames Animation is a laborious task.  An animated movie, playing at 24 fps, at a total duration of 90 minutes, requires 129600 individual frames to be drawn and painted.  Each of these frames, at least before the advent of computer animation, must be drawn by hand.  To facilitate production, there are Key Frame animators and In-between Frame animators. 

Key Frames

Key Frames are frames that act as reference points, usually illustrating a major event in time.  For example, if you were to create an animation of a runner practicing a 100-meter dash, you could have the following Key Frames:

Key Frame 1:  Runner Stretching
Key Frame 2:  Runner crouched in the blocks
Key Frame 3:  Runner at full stride
Key Frame 4:  Runner crossing the line

The Key Frame artist (or a team of Key Frame artists) is responsible for drawing each Key Frame.  If this entire sequence is to last for 15 seconds (at a frame rate of 24fps), we’ll obviously need more than four frames to animate it (360 frames in total).  This is where the In-between Frame artists come in.  A storyboard is received which diagrams the major events in the animation.  Storyboards are also used for live action films and for design planning in general. 

In-between Frames
The In-between artists are responsible for drawing the frames in between the Key Frames.  For example, by examining the Runner standing straight, and then crouched in the blocks, the In-between artists know they have to draw the transition from a standing position to a crouching position.  As a result, this process is called In-betweening, and in Fireworks is referred to as Tweening.  Fortunately, in some cases, you act as the Key Frame artist while Fireworks acts as the In-between artist.