Beginner's Guide to Adobe Flash/Filters and Blend Modes/Animating Filters with Motion Tweens
Adobe has done a great deal of engineering to make it as easy as possible to combine filters with motion tweens for animated effects. The result is a very intuitive system that works behind the scenes to support tweens while preserving editable filter settings.
Filters are not necessarily incompatible with shape tweens, but because filters can only be applied to symbols or text fields and shape tweens can only be applied to primitive shapes, filters and shape tweens never get a chance to work together. The only workaround for this rule is to create a shape tween inside of a Movie Clip and then apply a filter to the Movie Clip. In this case, the final visual result is a combination of a shape tween and a filter, but they remain on separate timelines.
You can apply a filter to an item and then tween it, or you can select an item that has been tweened and add a filter to enhance the motion - in most cases, you'll get exactly the animated effect you were hoping for. The only time you'll need to know what is going on behind the scenes is when you don't get the result you want on the first try.
Here are some notes that should help you troubleshoot if things go wrong when you try to combine filters and Motion tweens:
+ Filters "stick" to symbol instances, so if you insert a keyframe (with the same content as the initial keyframe), and set up a Motion tween, the settings and the stacking order in the live list will automatically match in the first keyframe and the last keyframe of the tween.
+ If you add a filter to a symbol in one keyframe of a tween, Flash automatically adds a matching filter with all the settings adjusted to create "no effect" to the symbol in the other keyframe. This is also called a "dummy filter" because it will have no visible effect on the symbol, but it is required to support the tween.
+ If you remove a filter from a symbol in one keyframe of a tween, Flash automatically clears the matching filter from the other keyframe.
+ If you apply different filters (or different combinations of filters) on two different keyframes and then apply a tween, Flash will analyze the symbol with the most filters and apply dummy filters to the symbol in the other keyframe to support the tween. The visual difference between the two symbols will be interpolated in the span of the tween.
+ You can modify filter settings to create a visual change from the first keyframe to the last keyframe in a Motion tween. The differences will be tweened evenly across the span unless you use easing to adjust the interpolation.
+ The knockout and type of gradient (such as inner, outer, or full) filter settings will not interpolate properly as part of a tween if they are set differently on the beginning and end keyframes. If the filter options in the first keyframe and the end keyframe of a tween are inconsistent and cannot be interpolated properly, Flash will apply the options set in the first keyframe to the frames in the span of the tween.