Beginner's Guide to Adobe Flash/Filters and Blend Modes/Applying Compound Blend Modes
Alpha and Erase blends are a great complement to Flash's standard masking tools-which can be counter-intuitive at times. If you want to create a cutout in a shape using a traditional mask, you actually have to create a shape on a mask layer that covers all the areas except the area you wish to cut out. If you have been working in Flash for a while, this workflow is proba- bly second nature, but when it comes to more subtle mask effects, like gradients or irregular shapes, it can be a headache to have to reverse-engineer a mask graphic. With Alpha blends, what you see is what you get - or rather, what you don't see is what you won't get! The steps for creating a compound blend are as follows:
1. Create a Movie Clip with content that will function as the base image (or convert an existing graphic that you want to mask into a Movie Clip).
2. Open the Movie Clip in Edit mode to access the Movie Clip timeline: Double-click an instance on the Stage or the symbol name in the Library list.
3. Create a new layer on the Movie Clip timeline above the existing content that will be the base image for the Alpha or Erase blend. To protect the base image(s), you may want to lock all layers but the new layer.
4. In the new layer, create a graphic that will act as a mask- blend masks are the oppo- site of normal Flash layer masks in that the content in the Alpha or Erase blend symbol instance will define an area to make invisible in the base image rather than define an area to make visible.
5. Convert the content on the blend layer into a Movie Clip or Button symbol.
6. Select the symbol instance and position it on the Stage (still on the base image Movie Clip timeline) to overlap the base image so that it defines the area you want to Erase or Alpha out, then use the Blend menu in the Properties panel to apply an Alpha or Erase blend mode. The content of the blend image will disappear, but don't panic-continue to the next step to complete the compound blend.
7. Return to the Main Timeline: Double-click an empty area of the Stage or use the Scene button above the Timeline.
8. Select the parent symbol instance (that contains your base image and the currently invisible blend image), and use the Blend menu to apply a Layer blend. (If you opened the base symbol from the Library in Step 2, make sure you have an instance dragged onto the Stage on the Main Timeline so you can apply the Layer blend mode to the instance.)
9. Voila!You should see the content of your blend image punched out (Erase blend) or rubbed out (Alpha blend) of the base image-either the background color of the Flash movie or any underlying images on the Stage will be visible through the empty areas created in the base image.
In addition to supporting a more intuitive workflow for creating masks and enabling Alpha- based masks, compound blends can be used to create animated transition effects. Continue to the next section if you would like to try using an Alpha blend to create an animated color fade effect.