Example: Drawing Gradients on the Alpha Channel

Apply a gradient on an alpha channel to create a partially transparent image. If you add gradient objects in Paint, and the Paint operator is on a layer in a composite, the partially transparent images can be used to create montages and other compositions.

Use a black/white gradient on the alpha channel to create a picture that gradually becomes transparent.

To create a partially transparent object:

1. Create a new Composite operator and import a layer. See Creating Composites.

In this example, the following image is used.



2. Select the layer in the Workspace panel, then chose Operators | Paint to add a Paint operator to it.

Paint opens.

3. Choose Window | View Mode | Alpha to switch to Alpha View mode.

The viewport turns completely white.

Note: If the imported image sequence already contains an alpha channel, the viewport will not be completely white.

4. Draw a filled rectangle object over the entire viewport.
5. Select the filled rectangle object in the viewport, then click the Gradient color mode button on the Modes controls.



6. Click the Gradient button.

The Gradient controls appear.

7. Add black and white color gradient tags to the Color gradient bar as shown here.



8. Click the Linear Gradient button and click the down arrow button on the direction control box.



Your filled rectangle should look like this:



The dark areas of your gradient will become transparent; the white areas remain opaque. The darker the grays on the alpha channel, the more transparent they are.

9. Choose Window | View Mode | Transparent.

In this View mode, you can see exactly to what degree your image is transparent.



Note: The small checkerboard pattern that appears under the image indicates the level of transparency. You can customize the pattern by choosing File | Preferences | Transparency.

10. In the Workspace panel, double-click the composite to load it into the active viewport.
11. Choose File | Import Footage to import a background layer.

In this example, the following layer is used.



12. Send the imported layer behind the original layer. You can do this by adjusting the stacking order or by selecting the layer, then choosing Object | Send to Back.
13. The transparency in the foreground is automatically maintained.
14. Double-click the composite in the Workspace panel to see the following result.



Note: Use Paint operators to create as many partially transparent layers as necessary, then use them as layers in your composite.