From the book
Editing a mask
The mask looks pretty good, but instead of masking the information inside the monitor, the mask has removed everything outside the monitor. So you need to invert the mask. (Alternatively, you could change the mask mode, which is set to Add by default.)
About mask modes
Blending modes for masks (mask modes) control how masks within a layer interact with one another. By default, all masks are set to Add, which combines the transparency values of any masks that overlap on the same layer. You can apply one mode to each mask, but you cannot change a mask’s mode over time.
The first mask you create interacts with the layer’s alpha channel. If that channel doesn’t define the entire image as opaque, then the mask interacts with the layer frame. Each additional mask that you create interacts with masks located above it in the Timeline panel. The results of mask modes vary depending on the modes set for the masks higher up in the Timeline panel. You can use mask modes only between masks in the same layer. Using mask modes, you can create complex mask shapes with multiple transparent areas. For example, you can set a mask mode that combines two masks and sets the opaque area to the areas where the two masks intersect.
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Inverting the mask
For this project, you need everything inside the mask to be transparent and everything outside the mask to be opaque. You’ll invert the mask now.
Select the office_mask layer in the Timeline panel, and press the M key to see the Mask Path property for the mask.
There are two ways to invert this mask: by choosing Subtract from the Mask Mode pop-up menu, or by selecting the Inverted option.
Select the Inverted option for Mask 1.
The mask inverts.
- Press F2, or click an empty area of the Timeline panel, to deselect the office_mask layer.
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If you look closely at the monitor, you will probably see portions of the screen still appearing around the edges of the mask.
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These errors will certainly call attention to changes being made to the layer, and they need to be fixed. To fix them, you’ll change the straight lines to curves.
Creating curved masks
Curved or freeform masks use Bezier curves to define the shape of the mask. Bezier curves give you the greatest control over the shape of the mask. With them, you can create straight lines with sharp angles, perfectly smooth curves, or a combination of the two.
- In the Timeline panel, select Mask 1, the mask for the office_mask layer. Selecting Mask 1 makes the mask active and also selects all the vertices.
- In the Tools panel, select the Convert Vertex tool (
), which is hidden behind the Pen tool.
- In the Composition panel, click any of the vertices. The Convert Vertex tool changes the corner vertices to smooth points.
Switch to the Selection tool (
), click anywhere in the Composition panel to deselect the mask, and then click the first vertex that you created.Two direction handles extend off the smooth point. The angle and length of these handles control the shape of the mask.
- Drag the right handle of the first vertex around the screen. Notice how this changes this shape of the mask. Notice also that the closer you drag the handle to another vertex, the less the shape of the path is influenced by the direction handle of the first vertex, and the more it is influenced by the direction handle of the second vertex.
- Once you are comfortable moving the handles, position the handle of the upper-left vertex as in the preceding figure. As you have seen, you can create very fluid shapes.
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Breaking direction handles
By default, the direction handles of any smooth point are connected to one another. As you drag one handle, the opposite handle moves as well. However, you can break this connection to get greater control over the shape of the mask, and you can create sharp points or long, smooth curves.
- Select the Convert Vertex tool () in the Tools panel.
- Drag the right direction handle of the upper-left vertex. The left direction handle remains stationary.
- Adjust the right direction handle until the top segment of the mask shape more closely follows the curve of the monitor in that corner. It doesn’t have to be perfect.
- Drag the left direction handle of the same vertex until the left segment of the shape more closely follows the curve of the monitor in that corner.
- For each of the remaining corner points, click with the Selection tool, and then repeat steps 2–4 until the shape of the mask more closely matches the curvature of the monitor. If you need to shift a corner point, use the Selection tool.
- When you’re done, deselect the office_mask layer in the Timeline panel to check the edge of your mask. You should not see any of the monitor screen.
- Choose File > Save to save your work.
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