The process of using computer graphics to generate animated images is called Computer Animation. This simply refers to moving images. To create the illusion of movement, an image is displayed on the computer monitor and repeatedly replaced by a new image that is similar to it, but advanced slightly in time (usually at a rate of 24 or 30 frames/second). This technique is identical to how the illusion of movement is achieved with television and motion pictures.

Modern computer animation usually uses 3D computer graphics, but 2D computer graphics are still used for stylistic, low-bandwidth, and faster real-time renderings. For 3D animations, objects are built on the computer monitor and 3D figures are rigged with a virtual skeleton. In 2D figure animations, separate objects (illustrations) and separate transparent layers are used with or without a virtual skeleton. Then the structures of the figure are moved by the animator on key frames. The differences in appearance between key frames are automatically calculated by the computer in a process known as morphing. Finally, the animation is rendered.

With 3D animations, all frames must be rendered after the modeling is complete. For pre-recorded presentations, the rendered frames are transferred to a different format or medium, such as film or digital video. The frames may also be rendered in real-time as they are presented to the end-user audience. Low bandwidth animations transmitted via the internet (e.g. Adobe Flash, X 3D) frequently use software on the end-users computer to render in real-time as an alternative to streaming or pre-loaded high bandwidth animations.

In most 3D computer animation systems, the animator creates a simplified version of a character’s structure, which is analogous to a skeleton or stick figure. The position of each segment of the skeletal model is defined by animation variables, or Avars for short. The computer doesn’t usually render the skeletal model directly (it is invisible), but it does use the skeletal model to compute the exact position and orientation of that certain character, which is eventually rendered into an image. Thus by changing the values of Avars over time, the animator creates motion by making the character move from frame to frame. Rather than set Avars for every frame, they usually set Avars at strategic points (frames) in time and let the computer interpolate or tween between them in a process called key framing. Key framing puts control in the hands of the animator and has roots in hand-drawn traditional animation.

As a result of the dissemination of the Internet and the digital media outlets, the creation and distribution of animated content have increased dramatically on an international scale and in every relevant sector: advertising, TV series and specials, feature films, not to mention the growing demand for animations in the fields of video games and cross and trans-media projects for the Web, tablets, and mobile devices.