Visual Processing and Film
Whether you're talking animation or live action photography filming, the basic science of moving pictures is the same. When a person views a moving object in real life, the human brain retains the image of a moving object for longer than that image is actually present. This creates an opportunity to convince the brain's image processing centers that a series of fast, still images are actually moving pictures. While live action filming takes a series of still, chronological images of moving objects to be played back in sequence, animation synthesizes this process through the creation of individual frames by artists. The human brain will perceive motion when watching a series of moving images presented at a speed as slow as 10 frames per second, but the motion will appear jerky. A rate of 16 images per second creates an impression of a moving image virtually indistinguishable from live motion.
Traditional animation is created when an animator, or group of animators, makes a series of still images which are photographed and used to create film, or played in a sequence using a computer program. Each individual drawing represents a fraction of a section of the progress of a moving image. The art of animation drawing is therefore highly complex because it requires not only the skill of drawing, but the skill of observing and capturing very gradual changes in movement and lining up each drawing accurately with the last. The process of hand animation is usually streamlined through the use of animation cells. An animation cell is a sheet of clear plastic which is laid over a finished drawing. The finished drawing contains the background of the animated scene and any objects that won't be moving during the scene, while a series of cells are painted with the progressive images of the characters and moving objects. This saves time by requiring the animator(s) to only draw multiple images of the few moving objects rather than the entire scene. It also keeps the background consistent.
Computer animation is the process of creating animation with computer imaging. It is used for television, ads and video games and can be created in a number of ways. Three-dimensional image design programs create virtual models of objects in a movable, computer generated view. Once an object and settings are fully created, the computer program can be used to create virtually any "camera angle" image of the object and record a still frame to be used for animation. Once this is finished, the animation can be created in one of two ways: animators can move the models and record all individual images to be assembled into frames (as they are with traditional animation), or a computer can generate some of the frames automatically. The latter is done through the use of "key frame" programs that generate automatic gradient images between two different pictures. For example, a key frame program that was given an image of a ball as it hit the ground and an image of a ball that had bounced three feet in the air could automatically animate the bounce by generating "in-between" images of the ball moving gradually higher in the air.
Animation can also be created using a more traditional process on a computer. Instead of creating animation frames using modeling programs or ink and paper, artists draw two-dimensional frames using image editing programs. The resulting animation has the appearance of being hand-created, but can be made with the efficiency of computer animation. Clear cells are not required, since each frame can be saved, then instantly copied before being altered to become the next frame. This gives the animator more freedom to animate a higher percentage of objects in the composition (since there is no need for a fixed background), while eliminating much of the troublesome work involved in lining up images with one another.