he first step in mastering any new media or technology is analyzing its roots in what you already know and use. Admittedly, various styles of animated graphics are not easy to classify, even using the approaches we've developed for the analysis of static dynamism. There is, however, one useful principle that can help you understand various animation features: Always base your analysis upon the everyday perception patterns that we use in recognizing and controlling motion of physical objects.

A recognized champion in imitating the physical world - or, more precisely, some aspects of physical bodies' appearance - is the 3D graphics and its animated variety, to be discussed in a next section. One could say that all animation styles and approaches try, with different degree of success, to either imitate (in relatively simpler cases such as 3D) or creatively play upon (in more imaginative animation styles) the momentary, subconscious expectations that we project on any moving object we see, be it on screen or in real life.

The first thing we notice when we set about analyzing real-world motions is that change in position never comes alone. Most often, a spatial displacement is accompanied by changes in shape, color, and texture of the object (more precisely, of the object's perceived image). So, in the foundation of an animator's skills lies the ability to persuasively combine different aspects of motion. Let us examine these visual aspects of objects from the animation viewpoint.

Shape is perhaps most affected by an object's actual motion, and it's easy to understand why: both shape and position are spatial features, and when we put the object in motion as a whole, it is only natural to expect that parts of its contour will, to same extent, displace relative to each other. When this is neglected in computer animation, the resulting "solid body" motion may seem flat, rigid, mechanistic.

This is especially true for animations with any animate characters (pun intended), such as human figures, whose visible outline changes significantly even with slightest body motions. One of the components of Disney's everlasting fame is the charmingly lifelike flexibility of his "rubber," elastic characters that never stay solid for more than a fraction of a second. Admittedly, this technique is very labor-consuming; Disney's animators even went on a strike in 1941 demanding salaries increase, and the studio did not produce feature-length animations after 1950s because of rising labour costs. Still, we can learn a lot from Disney's classic examples of "live shape" animation.

Even inanimate objects can greatly benefit from skillfully varying their shape during motion. Here, some simple physics should be your guide in deciding what should be stretched, skewed, or distorted, in what direction and to what extent. One of the most common examples, a horizontally scrolling line of text, feels much more natural if its motion is accompanied by changing the slant and the tracking distance between letters (Fig. 1).