Drawing and animating masks in Video by Zaweba
Draw rectangle, ellipse, star, polygon, pen and freehand masks in Video by Zaweba, combine them, feather and animate them, and select by colour.
Masks decide which part of a picture shows. Everything inside is kept and everything outside is clear, or the other way round. It sounds simple, but masks are behind a great many effects: blurring a face, brightening one part of a shot, shaping a picture into a circle, revealing a scene through a moving window. Video by Zaweba has clipping masks on any picture clip, with several ways to draw them.
Making a mask
One click makes a rectangle, an ellipse or a star. These are the quickest masks, and often all you need. Rectangle masks can have rounded corners, which is a tidy look for picture in picture.
For other shapes, draw on the preview. A polygon is a set of straight sides; click to place each corner. A pen curve uses curved sides; drag as you place each point to pull out Bezier handles and bend the line. Freehand lets you draw an outline as you would with a pencil.
Colour masks work differently. Instead of a shape, they select a range of hue, saturation and brightness. Pick a colour range, and the mask covers everything in the picture with those colours. This suits things that are hard to draw round, like a blue sky or a red coat.
Edit a mask's points directly on the preview. Drag points and their handles to reshape the outline. Ctrl+click on the outline to add a point. Alt+click a point to delete it. Zooming the preview in helps when working on a detailed edge, and the masks stay lined up at every zoom level.
Combining masks
A clip can have more than one mask, and each one can add, subtract, intersect or difference. Add combines two shapes. Subtract cuts one shape out of another, so you can make a ring by subtracting a small ellipse from a larger one. Intersect keeps only the overlap. Difference keeps the parts that do not overlap.
Any mask can be inverted, so the outside shows and the inside is clear.
Feather, expansion and more
Each mask has feather, expansion, opacity, move, scale and turn. Feather softens the edge, which is what makes most masks look natural. A hard edge is right for graphics, but for blending something into a shot, a soft edge hides the join. Expansion grows or shrinks the mask from its outline without redrawing it. Opacity sets how strongly the mask applies. Move, scale and turn reposition the mask as a whole.
All of these can be animated with keyframes, as can the shape itself, so a mask can grow, travel and change over time.
Jobs masks do
Blurring a face or a number plate. Duplicate the clip on the track above, blur it, and mask the blurred copy to the area. Feather the edge and animate the mask to follow, or use mask tracking to do the following for you.
Grading one area. Brighten a face that is in shadow, or darken a sky, by masking a graded copy.
Shaping pictures. A round picture of a speaker, a star shaped reveal, or a window into another scene.
Removing distractions. Mask a clean part of a shot over a distraction on the track below.
Masks that give themselves away
Leaving feather at zero on a natural shot is the most common one. Hard edges are easy to spot. Add a few pixels of feather and check.
Drawing too many points makes a mask hard to adjust and to animate. Use the fewest points that follow the shape.
Animating a mask by hand on every frame is slow. For anything that moves, try mask tracking first.
Masks and their companions
Masks in Video by Zaweba work alongside SVG masks for complex shapes, mask tracking for moving subjects, and track mattes for putting video inside text or logos. Together they cover almost any job where only part of a picture should show.
