Combine multiple masks on a video effect
When defining the area of a clip effect, including a color correction, you may find that it’s impossible to create the mask shape you need using only one mask. For example, when masking a shape with a hole in it, you need at least two masks—one set to Add to mask the overall object, and a second set to Subtract to cut out the hole.
You can set masks to interact in different ways using mask blend modes. For example, you can add mask shapes together to create a combined mask, subtract a mask shape from other masks, and intersect masks.
You can add an unlimited number of effects to a clip, but the following rules dictate how you can combine multiple masks within a single effect:
You can add an unlimited number of shape masks to an effect.
You can add only one color mask to an effect.
Mask blend modes interact within a single effect—not across multiple effects.
Add, subtract, and intersect masks
Add a video effect to the clip from the Effects Browser.
You can add almost any kind of video clip effect, including the Color Correction effect. However, effects in the Keying and Masks categories in the Effects Browser do not have the built-in effect masking tools described here.
To open the Video inspector, choose Window > Show Inspector (or press Command-4).
To add an additional mask to the effect, move the pointer over the effect name in the Video inspector and click the Apply Effect Masks button that appears to the right of the effect name.
The new mask appears below the effect name in the Video inspector, with the blend mode to the right. By default, new shape masks appear at the top of the list in the Add mode, and new color masks appear at the bottom of the list in Intersect mode.
Note: You can rearrange the order of the masks within a given effect. For more information, see “Reorder masks,” below.
To change how a mask interacts with other masks applied to the effect, click the pop-up menu next to the mask name and choose a blend mode:
Add: Applies the effect to the area inside the mask shape selection. If two or more masks are set to Add, the masks are merged.
Subtract: Removes the effect from the area inside the mask shape, including areas that overlap with other masks.
Intersect: Applies the effect to any area inside the mask shape that overlaps with other masks set to either Add or Intersect.
Note: At any time, you can invert all masks for a given effect. For more information, see Invert effect masks for a clip.
The order in which you apply shape and color masks can affect the final output. The Add, Subtract, and Intersect modes operate sequentially, starting at the top of the mask list in the Video inspector. By default, new shape masks appear at the top of the list in Add mode, and new color masks appear at the bottom of the list in Intersect mode. You can reorder masks to achieve the effect you want.
To apply two or more masks to an effect, follow steps 1 through 6 in “Add, subtract, and intersect masks,” above.
The masks are listed below the effect name in the Video inspector.
To change the mask order, drag masks up or down in the list.
For an example of how you might use shape masks set to the Intersect blend mode to isolate one area of a color mask, see Add shape masks to a color mask.