Animation. Representation of objects as they vary over time. Traditionally, based on individual drawing or photographing the frames in a sequence

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1 6 Animation Animation Representation of objects as they vary over time Traditionally, based on individual drawing or photographing the frames in a sequence Computer animation also results in a sequence of images, but these are created by software SWE MULTIMEDIA SYSTEMS 1

2 Animation Animation is made from a series of stills and relies on something called persistence of vision Persistence of vision is the phenomenon were an object on the eye s retina remains for a brief time after viewing This means that a series of still images which vary slightly, if shown rapidly will give the illusion of movement If each of the eight pictures below were shown at the same point in rapid succession, the result would be a rotating arrow. Animation TV gives the illusion of continuous movement by showing the stills at the rate of 30 frames per second Today, most animation is performed by computer. Examples are Bugs, Toy Story, and the BBCs Walking with Dinosaurs The computer will produce a wire frame of the scene, then apply textures and light effects before moving onto the production of the next frame, each of which may take hours or even days to produce SWE MULTIMEDIA SYSTEMS 2

3 Why animate? Animate means to bring to life Because it is a good (and sometimes less expensive) way to show/say some things The power of motion Visual effects Wipes, fades, zoom, dissolve Animated presentations Animated applications Animated Web applications Applications Animation has been used for entertainment, advertising, instruction, art and propaganda on film or video; it is also employed on the World Wide Web and in multimedia presentations Microsoft DirectAnimation A high-level DirectX APIs and controls that provides rich support for animation Comprehensive support for different media types A uniform time and event model that frees user from frame-level details Can be used to build high-performance animation in a variety of environments HTML, JavaScript, VBScript, Java, C++, VB See DirectX Media SDK SWE MULTIMEDIA SYSTEMS 3

4 Animation Packages Frame-based animation Tweening Image creation and image animation 2-D image, 3-D image Animation files store a series of frames Wireframe (mesh) Surface texture Morphing Rendering Web Animation Flash from Macromedia plasma from Discreet 3-D Animation 3ds max from Discreet (a division of AutoCAD) SOFTIMAGE XSI from Softimage (a division of Avid Technology) Maya from Alias Wavefront (a division of SGI) What we are going to talk about? Cel (and flipbook) animation Sprite, path, vector animation Key frames and tweening Character animation 2D vs. 3D and other things SWE MULTIMEDIA SYSTEMS 4

5 Cel Animation Cel Animation is the technique used to produce the old Tom & Jerry cartoons and the new computer generated Disney cartoons It draws its name from the celluloid films used in old hand drawn animations Moving elements in a scene are drawn on transparent materials known as cels (celluloid), now replaced by acetate or plastic The celluloid films permitted layering, where the background to a sequence may be drawn on one or more films and then the films containing the animated characters place on top Such animation starts with the production of keyframes, which are the first and last frames of an action scene 24 frames per second Cel Animation The frames in between the keyframes are then produced using a process known as tweening Sketch onto a cel with pencil When the pencil frames are satisfactory, they are permanently inked Tweening is where the number of frames which must appear between keyframes is calculated and the frames drawn Tweening may be performed by computer if the frames are not too far apart Only the moving elements on the cel need to be redrawn for each frame, the fixed part of the scene need only be made once Animation cels are layered to produce a single animation frame SWE MULTIMEDIA SYSTEMS 5

6 Flipbook (Simple) Animation Timer Rotate through several pictures Change location Examples flying butterfly flip book bouncing ball problem: takes too much time (especially over the Internet) compression techniques are usually proprietary (different type of images!) Palette Animation Simulate motion by color cycling rapidly changing the colors of selected entries in a color palette or switching between multiple palettes e.g. running water quick method of creating animation that requires very little memory GDI functions SelectPalette SelectPaletteEntries RealizePalette CreatePalette AnimatePalette SWE MULTIMEDIA SYSTEMS 6

7 Sprites and Paths Sprite: a part of the animation which moves independently of the rest Anything can be a sprite: ball, animal, human, A sprite can be attached to a path (or vice versa), so that successive sprite positions are located on a path Sprite can animate in-place, or move along a path, or both Splines and Vectors Paths can be linear More often, paths follow a spline curve Sprites can be described as raster objects SWE MULTIMEDIA SYSTEMS 7

8 Key Frames Most important frames are drawn first: key frames establish the main dramatic poses, define the flow of actions, and create the overall graphic style of the animation Tweening Tweening: frames are inserted between the key frames Computer can do much of the tedious work SWE MULTIMEDIA SYSTEMS 8

9 Motion Interpolation Motion along an arbitrary line Computer performs the interpolation Special effects (rotation, resizing) can be specified along the line Morphing Transformation of one image into another A number of key points is set on both images Actual transformation is calculated on the basis of transformation (in both position and color) of key points More key points + more intermediate steps = smoother transformation SWE MULTIMEDIA SYSTEMS 9

10 2D vs. 3D Our perception of the world is three-dimensional 3D effects improve visual appearance 3D special effects can be added to 2D images (most drawing/painting programs can do it) 3D images can be generated from appropriate scene setups but: sophisticated applications are required Kinematics Considers only motion Determined by positions, velocities, accelerations Forward kinematics Low level approach where animator has to explicitly specify all motions of every part of the animated structure Each node in hierarchy inherits movement of all nodes above it Inverse kinematics Requires only the position of the ends of the structure Functions as black box - controls detailed movement of entire structure SWE MULTIMEDIA SYSTEMS 10

11 Forward Kinematics Animator specifies joint angles Computer finds position of end-effector: X Inverse Kinematics Animator specifies end-effector positions Computer finds joint angles SWE MULTIMEDIA SYSTEMS 11

12 Kinematics Summary Forward Kinematics Animator has complete freedom over the movements of any part of the structure Amount of work is function of the complexity of the structure, much more expensive when dealing with complex structures Inverse Kinematics Does not leave much scope for the animator to inject character into the movements Model does not possess the interpretation of a human being Overall movement of structure depends on the formula same footprints, same movements Character Animation Often the trickiest part many simultaneous movements involved Faces are very difficult to animate SWE MULTIMEDIA SYSTEMS 12

13 3D effects Adding depth to 2D images Effects like extruding shadows highlights embossing texturing special lighting effects Step 1: Creating Storyboards detailed storyboard drawings are created as the blueprint for the action and dialog there can be as many as 3 to 4 thousand such drawings for a feature-length movie (which comes to about one drawing every two seconds or so) they are revised many times during the creative development process SWE MULTIMEDIA SYSTEMS 13

14 Step 2: Modeling specialized animation software is used to create three-dimensional computer models of characters, props, and sets computer models describe the shape of the object as well as the motion controls that the animators use to create movement and expressions Step 3: Animation specialized animation software allows animators to orchestrate the motion in each scene by defining key frames or poses computer automatically creates the "in-between" frames animators neither draw, nor paint the scenes, as is required in traditional animation process SWE MULTIMEDIA SYSTEMS 14

15 Step 4: surface characteristics, including textures, finishes and colors, are added to every object in the scene textures can simulate a wide variety of appearances textures may be 2D images or procedural algorithms additional properties: reflectivity, transparency Step 5: Using "digital lights," every scene is lit in much the same manner as stage lighting Key, fill and bounce lights and room ambience are all defined and used to enhance the mood and emotion of each scene SWE MULTIMEDIA SYSTEMS 15

16 Lighting is the key Key light the brightest Fill light opposite the key light, reduces contrast and shadows Back light reduces shadows, separates the subject from the background Step 6: Rendering rendering software (Pixar's proprietary RenderMan) "draws" the finished image by computing every pixel of the image from the model, animation, shading, and lighting information once rendered, final images are transferred to film, video, or CD-ROM SWE MULTIMEDIA SYSTEMS 16

17 Stages of 3D Animation 3D modeling Motion specification Motion simulation Shading, lighting, rendering Postprocessing Motion Generation Keyframing Allows fine control but does not ensure the naturalness of results Procedural Methods and Motion Capture Realistic motion, however allows little control over fine details SWE MULTIMEDIA SYSTEMS 17

18 Procedural Methods Computer procedurally follows the steps in an algorithm to generate motion Simulations Passive systems No internal energy source, moves only when an external force acts on them Active systems Internal source of energy, can move of their own volition Easy to generate a family of similar motions Particle systems Flexible surfaces Motion Capture capture of motion of (human) actor whole body, upper body, face Technology optical, magnetic, mechanical Employs special sensors (trackers) to record motion of human performer Problems Difficult to accurately measure motion of human body clothes may shift, etc If object used to generate recorded motion and graphical object have different dimensions -> animation will have noticeable flaws. SWE MULTIMEDIA SYSTEMS 18

19 Virtual Reality Head-mounted displays Data gloves track hand movements Haptic interfaces provide tactile feedback Haptics is the study of human touch and interaction with the external environment via touch 'Haptic' comes from a Greek term meaning 'able to lay hold of' For flight and industrial simulation, games 6 Animation 6.2 Web Animation SWE MULTIMEDIA SYSTEMS 19