Using Onion Skinning

Onion skinning is a traditional animation technique that enables you to see and manipulate objects before and after the current frame. When you are creating frame-by-frame animation, this helps you position objects in each frame without flipping back and forth between frames. When onion skinning is turned on, objects in frames before and after the current frame are dimmed so you can distinguish them from objects in the current frame.

In the preceding exercise, you placed circles in an arc to simulate them shooting out from the dot in the i. After you play your animation, suppose you decide you want to move one of the circles to change the shape of the arc. When you select a frame, you can't see the circles in other frames, and so in the next exercise you will use onion skinning to reveal the contents of other frames.

1.	Select frame 1 on the Frames panel. You can turn on onion skinning for selected frames or for all of the frames. The onion skinning marker is located in the left column of the Frames panel.
2.	Click the left column of frame 12. A vertical bar appears in the left column, indicating that onion skinning is on for the frames. You can also control onion skinning from the Onion Skinning pop-up menu. Open it by clicking the button in the lower-left corner of the Frames panel.
3.	Choose Custom from the Onion Skinning pop-up menu to change the opacity of the frames before and after the current frame. Onion skinning changes the opacity level of all frames other than the selected frame. You can use the Custom setting to change the opacity level. Setting the opacity level to 0 hides the contents; setting the opacity level to 100 makes the contents appear as if they are in the current frame. Choose Multi-Frame Editing to enable other frames to be selected and edited (even though they are dimmed). With onion skinning on, you can now position your objects on the canvas. You can even move the dimmed circles on other frames while you are in this mode. Note Onion skinning is turned off when you play the animation using the VCR controls.