After Effects
Using
Masks
A
mask is a shape that you draw onto a layer, which shows you only a selected
portion of the layer.
Remember, create a project folder and save your AE project to the folder.
Start
by creating a New Composition - don't forget to name it. Go ahead and set the resolution to 1920 x 1080, the fps to 59.97 and the Duration at 10 seconds.
Then add a Solid
Layer
> New > Solid
Set the Solid Settings to Make Comp Size and choose a
colour other than black in the colour box.
Back
in the Timeline you’ll notice that Mask 1 was created.
Pull down the mask’s disclosure triangle to reveal the mask options, which
includes Mask Path, Mask Feather and so on. Each of these options has a
stopwatch allowing you to animate them over the course of your clip.
To rotate around the centre of the mask itself,
you would need to relocate the anchor point. Simply click on the Pan Behind
tool (located in the Tool palette), which allows you to take hold of the anchor point to move it. But getting
the anchor point perfectly centred in your mask is tricky. A good way to measure
more accurately the centre point is to use a ruler as a guide, which you can
show in the Composition itself.
First, reset your Rotation - go to the Transform properties and you'll see to the right where it says Reset. Click it.
Hover
your pointer inside one of rulers until it becomes a double-arrow, then click
and drag from the Ruler over the mask and place the line in the middle of the
mask handles. Do this again using the other ruler. If you have a hard time positioning the line, go ahead and zoom in so you can see more closely what you're doing.
Where the lines intersect in the middle of the mask is where you can now drag your anchor point (don’t forget to click on the Pan Behind Tool first otherwise you'll move the entire mask). The anchor point should snap in the middle where the lines intersect.
Now you can Rotate the grid from the mask centre instead of from the Solid centre.
To change the shape of the Mask, make sure that Mask 1 is selected in your Timeline.
Click Command + T - this will add handles to the boundary box, which you can then grab with the pointer to push or pull and change the shape of the mask.
Animating the Mask Path is a great way to reveal items like the text in Lower Thirds.
More on using masks in later exercises.