How to use it. In Tweening, pick a frame on the timeline and drag the ball on the stage: that makes a keyframe there (a dot on the timeline). The frames between two keyframes are worked out for you (shaded). Choose a keyframe to change its shape, colour, size and rotation, and how the tween to the next keyframe moves (its easing). In Frame by frame, draw each frame yourself, with the onion skin showing the frame before. Play it, loop it, and change the frame rate. The challenges (on the right) set you a job and check it.
The ideas.
- An animation is a sequence of still frames shown quickly one after another; the eye sees movement (persistence of vision).
- The frame rate is how many frames are shown each second (frames per second, fps): film is 24 fps, television in New Zealand 25, many web animations 12 to 30. Duration = number of frames ÷ frame rate. A higher frame rate looks smoother, but needs more frames for the same length of time (a bigger file, more work).
- The timeline shows the frames in order. A keyframe is a frame where the animator sets exactly what's there.
- Frame-by-frame animation: every frame is drawn separately (like a flip book). Full control, but slow to make and a large file. Onion skinning shows the frame before (and after) faintly, so the next drawing can be lined up with it.
- Tweening (in-betweening): the animator sets the keyframes, and the software works out the frames between them. A motion tween changes position, size or rotation; a shape tween (morph) changes one shape into another (and can change its colour). Only the keyframes are stored, so the file is small and changes are quick.
- Easing changes the speed through a tween: ease in starts slowly and speeds up (a ball falling); ease out starts fast and slows down (a ball rising, or coming to a stop); linear is a steady speed, which looks mechanical.
- A loop plays the animation again from the start. For a smooth loop the last frame should lead back into the first.
File size. If every frame is stored as a bitmap, the size is frames × width × height × colour depth. A vector tween stores the shape once and a few numbers for each keyframe, so it's tiny until it's exported as a video or GIF, when every frame is made.
Common exam mistakes: mixing up frame rate and the number of frames (24 frames at 12 fps lasts 2 seconds, not 1); saying tweening draws the keyframes (the animator does; the software draws the frames in between); confusing a motion tween with a shape tween; describing easing backwards (ease in is slow at the start).
Objective: Cambridge International A Level IT (9626), animation: frames, frame rate and duration; the timeline and keyframes; frame-by-frame animation and onion skinning; tweening (motion and shape); easing; looping; file size.
Where this fits
- Cambridge: Cambridge A Level Information Technology (9626)
- NCEA Level 1 Digital Technologies: 92005 Develop a digital technologies outcome
- NCEA Level 2 Digital Technologies: 91893 Use advanced techniques to develop a digital media outcome
