Creating an Image Mask

In the previous exercises, you created transparent areas (an alpha channel) using Keying filters and a mask, which you created with the Circle Mask tool. Another way you can create transparency in an object is by using an image mask. An image mask creates transparency in an object by using the alpha channel from another object, such as a shape, a text object, a still image, or a movie.

In this exercise, you'll apply an image mask to the Surf video clips to create a puzzle look for the image. This technique is common in commercials and music videos.

Opening and Saving the Project

For this project, you'll be working from the Puzzle subfolder located in the Lesson_05 folder. Let's open the starting project and then look at the finished movie.

1.	Open the block puzzle start project, located in the Puzzle subfolder for Lesson_05. The project opens; it looks like white rectangle shapes on a black background in the Canvas.
2.	In the File Browser, double-click the block puzzle.mov file, which is located in the Puzzle subfolder. The block puzzle movie opens in the Viewer.
3.	Play the movie in the Viewer to see the finished version. As you can see, the Surf video clips are visible only on the rectangle shapes. It's a really cool effect, created using an image mask.
4.	Close the Viewer.
5.	Press the spacebar to play the block puzzle start project in the Canvas. A series of blocks appear and disappear on the Canvas. This effect was designed by creating shapes with the Rectangle tool and then varying the In and Out points for each shape in the mini-Timeline.