chapters 7 and 8
Animation
• Makes static presentations come alive.
• Visual change over time that can add great power to multimedia projects and web pages.
• Provided in both Macintosh and Windows multimedia applications.
Principles of Animation
Animation is possible because of two phenomenon:
• Persistence of vision – biological phenomenon which allows an object seen by the human eye to remain chemically mapped on the eye’s retina for a brief time after viewing.
• Phi – psychological phenomenon that explains the human mind’s need to conceptually complete a perceived action.
These make it possible for a series of images that are changed very slightly and very rapidly, one after the other, to seemingly blend together into a visual illusion of movement.
• Television video builds 30 entire frames or pictures every second; the speed by which each frame is replaced by the next one makes the images appear to blend smoothly into movement.
• Movies on film are typically shot at a shutter rate of 24 frames per second, but using projection tricks (the projector’s shutter flashes light through each image twice), the flicker rate is increased to 48 times per second, and the human eye thus sees a motion picture.
• Translate – to make an object travel across the screen while it changes its shape and move a few pixels for each frame.
• When frames are played back at a faster speed, the changes blend together and you have motion and animation.
Animation by Computer
• 2-D Animation – the visual changes that bring an image alive occur on the flat Cartesian x and y axes of the screen. Examples: color-cycling logo (where the colors are rapidly altered according to a formula), cel animation, or a button or a tab that changes state on mouse rollover to let the user know it is active. Simple and static, not changing position on the screen.
• Path animation – done in 2-D space which increases the complexity of an animation and provides motion, changing the location of an image along a predetermined path (position) during a specified amount of time (speed). Authoring and presentation software such as Flash and PowerPoint provide user friendly tools to compute position changes and redraw an image in a new location, allowing you to generate a bouncing ball or slide a corporate mascot onto the screen.
• 2½-D Animation – an illusion of depth (the z axis) is added to an image through shadowing and highlighting, but the image itself still rests on the flat x and y axes in two dimensions. Embossing, shadowing, beveling and highlighting provide a sense of depth by raising an image or cutting it into a background.
• 3-D Animation – software creates a virtual realm in three dimensions and changes (motion) are calculated along all three axes (x, y, and z), allowing an image or object that itself is created with a front, back, sides, top, and bottom to move towards or away from the viewer, or, in this virtual space of light sources and points of view, allowing the viewer to wander around and get a look at all the object’s parts from all angles.
Animation Techniques
Organize its execution into a series of logical steps:
• Think of all the activities that you wish to occur in the animation;
• Create a written script with a list of activities and required objects;
• Create a storyboard to visualize the animation;
• Choose the animation tool best suited for the job;
• Build and tweak your sequences: creating objects, planning their movements, texturing their surfaces, adding lights, experimenting with lighting effects; and positioning the camera or point of view; and
• Post-process your animation, doing any special renderings and adding sound effects.
• Cel Animation – techniques made famous by Disney which use a series of progressively different graphics or cels on each frame of movie film (which plays at 24 frames per second). A minute of animation may thus require as many as 1,440 separate frames, and each frame may be composed of many layers of cels.
• Cel – derived from the clear celluloid sheets that were used for drawing each frame, which have been replaced today by layers of digital imagery.
• Keyframes – the first and last frame of an action.
• Tweening – series of frames in between the keyframes are drawn in this process. An action that requires calculating the number of frames between keyframes and the path the action takes, and then actually sketching with pencil the series of progressively different outlines. Frames are assembled and then actually filmed as a pencil test to check smoothness, continuity and timing.
• Computer Animation – typically employs the same logic and procedural concepts as cel animation and use the vocabulary of classic cel animation—terms such as layer, keyframe, and tweening. The primary difference among animation software programs is in how much must be drawn by the animator and how much is automatically generated by the software.
In path-based 2-D and 2½-D animation, an animator simply creates an object and describes a path for the object to follow. The computer software then takes over.
In cel-based 2-D animation, each frame of an animation is provided by the animator, and then the frames are then composited (usually with some tweening available from the software) into a single file of images to be played in sequence.
For 3-D animation, most effort is spent in creating the models of individual objects and designing the characteristics of their shapes and surfaces. It is the software that then computes the movement.
• Kinematics – the study of the movement and motion of structures that have joints, such as a walking man.
• Inverse Kinematics – available in high-end 3-D programs such as Lightwave and Maya, is the process by which you link objects sucxh as hands to arms and define their relationships and limits.
• Morphing – a popular effect in which one image transforms into another. Tools that offer this effect can transition not only between still images but often between moving images as well.
Chapter 8
Video
Using Video
• Carefully planned, well-executed video clips can make a dramatic difference in a multimedia project.
• A clip of a speech from a famous personality is more effective than just having the text scroll on screen.
• Video standards and formats are still being refined as transport, storage, compression and display technologies take shape in laboratories.
• Broadcast television is moving from the analog National Television Standards Committee (NTSC) standard to the new (and evolving) Digital Television (DTV) standard.
• Digital video has supplanted analog video as the method of choice for making and delivering video for multimedia use.
Obtaining Video Clips
• Shoot new footage or acquire pre-existing content for your video clips..
• Pay for royalty of a video or footage if they are not in public domain.
• Shooting and Editing Video: (1) storyboarding – have a planned story to shoot; (2) shooting platform – use a tripod; (3) lighting; (4) chroma keys – allows you to choose a color or range of colors that become transparent, allowing the video image to be seen “through” the computer image (used in weather reports); (5) composition – avoid wide panoramic shots for computer use, close-ups and medium shots, head-and-shoulders or even tighter.
• Consider the amount of motion in the shot: the more the scene changes from frame to frame, the more information needs to be transferred from the computer’s memory to the screen, and the slower the playback speed will be.
• Keep the camera still instead of panning and zooming; let the subject add the motion to your shot: walking, turning talking.
Optimizing Video Files for CD-ROM
• Limit the amount of synchronization required between video and audio. AVI files are already interleaved. For Quicktime files, you should “flatten” your movie. Flattening means that you interleave the audio and video segments together.
• Use regularly spaced key frames, 10 to 15 frames apart, and temporal compression ca correct for seek time delays. Seek time is how long it takes the CD-ROM player to locate specific data on the CD-ROM disc.
• The size of the video window and the frame rate you specify dramatically affect performance. More data, slower playback.
• Use lower sampling rate and sample size to reduce the quantity of audio data.
• Defragment files before burning the master.
