• Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint
Share this Page URL
Help

Lesson 5. Horror Festival Ad > Setting a luma matte

Setting a luma matte

After setting up the composition that will serve as the final composition, you will import a half-second of a spooky-looking house that will overlay the Moon.psd layer. You will then use a luma matte to drop out the background of the movie footage using the luminance values of the matte file.

  1. In the Project window, click the New Composition button ( ) type Final Comp for the name, and retain the previous settings (frame size 320 x 240, 24 fps, 30 seconds duration). Click OK.

  2. Right-click (Windows) or Control-click (Mac OS) in an open area of the Project window and choose Import > Footage File. Select House.mov in the 05Lesson folder and click Open.

  3. In the Project window, drag the Moon.psd composition on top of the Final Comp composition, and then do the same with the House.mov footage item. This is a quick way to add footage, automatically aligning it to the center of a composition.


    Figure .


    The sky in House.mov needs to be masked out, so that the animated Photoshop comp background can show behind the house. A Bezier mask would work, but too much detail in an edge can make a Bezier mask impractical. An alternative method to creating a mask in After Effects is to generate a black-and-white image in Photoshop, import the file into After Effects, and use the image as a track matte.

  4. Right-click (Windows) or Control-click (Mac OS) in the Project window and choose Import > Footage File, select HMatte.psd from the 05Lesson folder, and click Open.

    The Photoshop image was created by exporting a frame of the house video as a Photoshop image using the Composition > Save Frame As command in After Effects. The exported still was used as a template in Photoshop to create a high-contrast image, in which white fills the area of the house and black fills the area of the sky.

  5. Drag HMatte.psd on top of the Final Comp icon in the Project window, to add it, centered, at the top of the stack.


    Figure .


  6. At the bottom of the Time Layout window, click the Switches/Modes button to display the Transfer Modes panel.

  7. From the TrkMat menu for the House.mov layer, select Luma Matte HMatte.psd. After Effects automatically turns off the video of the top layer (HMatte.psd), and a dotted line appears between the top two layers, indicating that one layer is used as a matte for the other.


    Figure .


    Using a luma matte lets you create a track matte from a layer that doesn't contain an alpha channel. After Effects uses the luminance values of the layer to create transparency. The lighter the pixel, the more opaque the corresponding pixel on the underlying layer appears. The white areas of the HMatte.psd image allow the underlying image (the House.mov layer) to appear completely opaque. The black areas of the HMatte.psd image allow the underlying image to appear completely transparent, so you can see the moon image beneath. Luma mattes work best with high-contrast files like the HMatte.psd image.


    Figure .



PREVIEW

                                                                          

Not a subscriber?

Start A Free Trial


  
  • Creative Edge
  • Create BookmarkCreate Bookmark
  • Create Note or TagCreate Note or Tag
  • PrintPrint