Slow in / Slow out / Pose to Pose - Walking animation

'Pose to Pose' is where the animator will create the main key frame(s) poses before working on the finer details in the animation. Once the main key frames are set, the frames between them can be done afterwards more easily. Creating Pose to Pose animations will save the animator time because the computer will generate the frames between the key poses and all the animator needs to do then is refine the frames between.

'Pose to Pose' animating is a good way to create looped animations such as walking, the start and end frames can be set so that the model is in the exact same position as in the first frame. 

Start and End frame pose

Half way-in frame pose

Once the beginning, middle and end frames are set the animator can then go in and add in frames between the main pose key frames. 

1/4th of the way in to the walk cycle

'Slow in and Slow out' is about increasing the realism of an animation; in real life an object will never completely stop moving in an instant, it will gradually slow down before coming to a stop. The idea is to make things flow more naturally where objects or limbs will gradually increase or decrease in their movement speed.

Increasing the Bias on the first frame

Decreased the Bias on the last frame

Changing the key frame 'Bias' in an animation will remove the popping effect which occurs when the object changes direction by making the movement smoother; it's slow in and slow out.

A visual example of what slow in and slow out looks like is this picture of a pendulum.

The ball slows down as it reaches the ends of it's swinging range but speeds up as it moves towards the middle.