Chapter 11Animation Multimedia Systems
Key Points • Animation is the creation of moving pictures one frame at a time. • Animation can be made using traditional methods and captured and digitized one frame at a time using a video camera or other input device. • Drawn or painted animation can be made using a graphics application. Painter provides special support for animation using frame stacks.
Key Points • Animations may be rendered as QuickTime movies, exported as a sequence of image files or stored as an animated GIF. • Layers can be used as the digital equivalent of cel to separate independently moving parts of an image. • Sprites are objects that can be positioned independently. Sprite faces are used to alter their appearance.
Key Points • In key frame animation, only important frames are stored explicitly; in-between frames are interpolated (tweened) from the key frames. • Flash is designed for producing simple vector animations, primarily for display on the World Wide Web. It is organized on a time line and provides automated tweening. • Easing in and easing out are used to produce more realistic movement than simple linear interpolation. • Key frame animation is applied to bitmapped images in making motion graphics in programs such as After Effects.
Key Points • In 3-D animation, interpolation is applied to the many numerical quantities that describe a three-dimensional scene. It requires huge resources and great skill to achieve good results. • Virtual reality (VR), has come to mean 3-D graphics that can be explored interactively. VRML and QuickTime VR are available formats for virtual reality. They come nowhere near the original concept of virtual reality as an immersive sensory experience of a synthetic world.
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.
Animate Means • Animate means “to bring to life” When played back at normal film or video speeds, the still characters, objects, abstract shapes, or whatever, that have been photographed in sequence, appear to come to life.
Frame Rate Requirement • Technically, 24 frames per second. • In practice, animation that does not require seamlessly smooth movement can be shot ‘on 2s’, which means that two frames of each drawing are captured rather than just one. This gives an effective frame rate of 12 frames per second for film or 15 for NTSC video.
Cel Animation • Those elements in a scene that might move are drawn on sheets of transparent material known as ‘cel’, and laid over a background drawn separately.
Stop-Motion Animation • Three-dimensional • This encompasses several techniques, but all use miniature three-dimensional set, like stage sets, on which objects are moved carefully between shots. The objects may include articulated figures, whose limbs can be repositioned, or solid figures whose parts are replaced, or substituted, between shots, to produce an effect of gestures, walking, and so on.
Clay Animation • It is similar stop-motion animation, but figures and other objects made out of a malleable modeling material, such as Plasticine (彩色塑泥), may be used instead; these can be manipulated between shots, to produce both natural movement, and otherwise impossible changes and transformations.
Hybrid Forms of Animation • Mixing cel and 3-D • Combining animation with live footage (連續鏡頭), such as Jurassic Park.
Captured Animation and Image sequences • Digital Technology • Using video camera and traditional animation methods together with digital technology offers much richer expressive possibilities to the animator working in digital media than purely computer-generated methods.
Frame Grabbing • For example, “Premiere” offers a Stop Frame command on its Capture menu. This causes a recording window to be displayed, showing the current view through the camera. • You can use this to check the shot, then press a key to capture one frame, either to a still image file, or to be appended to an AVI or QuickTime movie sequence. • You then change your drawing, alter the position of your models, or whatever, and take another shot. • Frames that are unsatisfactory can be deleted.
Ghost Image • “Premiere” offers an option allows you to see the currently and previously captured frames together, to help with alignment and making the appropriate changes. • Ghost image= previously captured frame
Multiple Animation Formats • When you captured a set of frames that form a sequence, “Premiere” can save it as QuickTime movie or a set of sequentially numbered images files.
Traditional Animation Supports • A film scanner will even allow you to digitize animation made directly onto film stock.For example, “Painter” provides special support for animators wishing to draw or paint animations digitally, in the form of features that resemble some of the ways in which traditional animators work with a stack of drawings.
Frame Stack • A “Painter” frame stack is a set of images, all of the same dimensions and colour depth. When you create or open a frame stack, you are provided with controls for navigating through it.
Onion Skinning • “Painter” offers an option allow you to make up to four frames adjacent to the one you are currently working on visible.
Rotoscoping • A process of painting on existing video frames.For example, “Painter” can paint onto or otherwise alter original video material, which is one way of adding animation to live action.
Web Page Animation File Formats(1) • GIF Files • GIF89a’s ability to store a sequence of images has been used to provide a cheap and cheerful form of small animation for Web page advertisements.
Web Page Animation File Formats(2) • GIF Shortcomings: However, even when GIF animation is properly implemented and enabled, it has many shortcomings. • Sound can not be added. • Colour palette is restricted to 256. • Images are losslessly compressed.
QuickTime • For animation of any duration, especially if it is accompanied by sound, the best result will be achieved using a video format, and QuickTime has become the standard.
Digital Cel • Cel in digital animation = layer • Layers allow you to create separate parts of a still image – for example, a person and the background of a scene they are walking through – so that each can be altered or moved independently.
Sprite Animation • We store a single copy of all the static layers and all the objects, together with a description of how the moving elements are transformed between frames. • This form of animation, based on moving objects, is called sprite animation.
Faces • Slightly more sophisticated motion can be achieved by associating a set of images, sometimes called faces.This would be suitable to create a ‘walk cycle’ for a humanoid character.
Key Frame Sample • QuickTime supports sprite tracks, which store an animation in the form of a ‘key frame sample’ followed by some ‘override samples’. • The key frame sample contains the images for all the faces of all the sprites used in this animation, and values for the spatial properties (position, orientation, visibility, and so on) of each sprite, as well as an indication of which face is to be displayed.
Override Samples • Override samples contain no image data, only new value for the properties of any sprites that have changed in any way. They can therefore be very small.
Dynamically Generated Sprite Animation • Instead of storing the changes to the properties of the sprites, the changed values can be generated dynamically by a program.
Key Frame Animation(1) • Breaking down complex tasks into small repetitive sub-tasks that could be carried by relatively unskilled workers • Character design, concept art, storyboards, tests • Trained animators: creation of key frames
In-betweening • The intermediate frames can be drawn almost mechanically by in-betweeners.
Flash • Flash is designed for producing simple vector animations, primarily for display on the World Wide Web. • A Flash animation is organized using a timeline, a graphical representation of a sequence of frames, similar to the timeline in video editing applications.
Flash’s Stage • Flash’s stage is a sub-window in which frames are created by arranging objects ( • vector images:WMF, EPS, AI…, • bitmapped images:GIF, JPEG, PNG, BMP…), and which is also used to preview animations.
Symbol • Graphical objects can be stored in a library in a special form, called symbol, that allows them to be reused. • Generating Key Frames • To animate a symbol, a key frame is selected in the timeline, and the symbol is placed on the stage; the current frame is then moved to the next key frame, and the symbol is moved, scaled, or otherwise transformed, to create the new frame.
Interpolation • In-between Frames Interpolation • Double-clicking anywhere in the timeline between frames brings up a dialogue, which allows you to specify that the in-between frames should be interpolated. • Flash’s interpolation is linear. • Flash does not offer an non-linear interpolation but borrows a technique from hand-made animations (easing in, easing out).
Two Problems with Linear Interpolation • Unnatural movement • Nothing really moves like this – motion begins and ends instantaneously, with objects attaining their full velocity as soon as they start to move, and maintaining it until they stop. • Solution: using hand-made animation
Easing In • The object accelerate from a standstill to its final velocity.
Easing Out • The converse process of deceleration.
Abrupt Change of Velocity • As the velocity graph clearly shows, this will appear as a sudden deceleration at that point in the animation. • Second problem
Abrupt Change of Velocity • Solution • Non-linear Interpolation • Using Bezier curves instead of straight lines to interpolate between key frames, smooth motion can be achieved. • Note that we do not mean that objects should follow Bezier shaped paths, but that the rate at which their properties change should be interpolated using a Bezier curve.
Motion Graphics • Interpolation between key frames can be applied to bitmapped images. • Since bitmaps do not contain identifiable objects, the use of layers to isolate different elements of an animation is essential. • These geometrical transformations are easily interpolated, but since we are now concerned with bitmapped images, they may require resampling, and consequently cause a loss of image quality.
After Effects • Leading desktop application for animation of motion graphics • Photoshop or Illustrator prepares the elements of an animation on a separate layer, and import the result into After Effects.
Repositioning Layers • Simplest animations • After Effects • Linear interpolation: Figs. 11.7, 11.9 • Bezier interpolation: Figs. 11.8, 11.10
Time-varying Filters • Motion graphics are the effects that can be achieved using time-varying filters on bitmapped images have more in common with graphic design than with mainstream cartoons or art animations. • Motion graphic effects can be applied to live video as well as to still images.
3D Animation • 3D models are defined by numerical quantities. • Object • Position in space • Rotation • Surface characteristics • Shape • Light source • Intensity • Direction • Camera • Position • Orientation
Motion paths in 3D • Add time -> 4D • Render 3D animation • Advanced shading algorithms • Ray tracing • A long time to process a single image
Behavior • A simple type of behavior • Making one object point at another • Camera is pointed at an object. • Spotlight pointed at an object. • Sunflower can be made to point at the sun • Have one object track another • Follow its motion at a distance • Camera • Behavior based on physical laws of motion
Kinematics • Study of the motion of bodies without reference to mass or force • It is only concerned with how things can move, rather than what makines them do so. • Jointed structure • Kinematic constraints • If upper arm is raised, lower arm and hand must come with it.
Inverse Kinematics • It is more useful to be able to position the object which is at end of the chain and then the object which is at end of chain move to accommodate it. • Works backwards from effect to cause • Poser • Many different ways • Minimizing the potential energy