Masks and Selective Effects

A mask limits an effect to part of the frame, so a correction or look applies only where you want it. Masks are how you brighten a face without lifting the whole shot, blur a single sign, or vignette the edges of an image.

What masks are used for

Without a mask, an effect applies to the whole frame. A mask defines a region - inside it the effect applies, outside it the picture is untouched (or vice versa). Common uses include:

• Brightening or darkening a subject or area.
• Blurring or pixelating a face, logo, or number plate.
• Vignetting to draw the eye to the centre.
• Selective colour - grading one part of the frame differently from the rest.

Shape masks

A shape mask defines the region you're affecting. Lightworks offers three shape types, plus import:

• Ellipse and Rectangle - clicking the shape button adds the shape to the viewer straight away, ready to reposition and resize. Most selective work starts here.
• Curve (custom shape) - click individual points on the viewer to outline any region; click the first point (the white square) to close the shape. Press Esc while drawing to start again. Ideal for irregular areas.
• SVG import - load a shape drawn elsewhere as an SVG file (ellipses, rectangles, polygons, polylines, and paths are supported).

Once a shape exists, position and size it over the area you want, and the effect is confined to it. You can drag a shape from anywhere inside it - no need to grab its centre point.

Feathering and opacity

Two controls make a mask blend naturally:

• Feather softens the mask edge so the effect fades in rather than showing a hard line - essential for invisible corrections.
• Opacity sets how strongly the effect applies inside the mask, so you can dial in a subtle change.

You can usually invert a mask, too, to apply the effect outside the shape instead of inside.

Following movement

When your subject moves, the mask needs to move with it. Keyframe the mask's position, size, and shape so it follows the action - even the individual points of a custom shape can be keyframed, so an outline can track an irregular moving subject (see Keyframes and animation). Set keyframes at a few points and let interpolation handle the frames between.

Applying masks to effects

A mask is attached to an effect, confining that effect to the masked region. Add the effect you want (a grade, a blur, a colour change), then mask it so it only touches the area you've defined. Stack a masked effect with others to build up a selective treatment.

Viewing and editing mask overlays

While editing a mask, Lightworks shows its shape as an overlay in the viewer so you can see exactly what's affected. Drag the shape's handles to resize and reshape it, and move it to reposition. A toggle on the viewer controls the overlay: switched on, mask overlays stay visible permanently; switched off, they appear only while the mouse is over the viewer. The viewer zoom helps you place mask edges precisely on fine detail (see Viewers and playback).

Mask controls are disabled while the effect itself is disabled, so you can't accidentally adjust a mask whose effect is switched off.

Common mask problems

• Hard, visible edge - increase the feather so the effect blends into the surrounding picture.
• Mask drifts off the subject - the subject moved but the mask didn't. Add keyframes to follow it.
• Effect on the wrong side - invert the mask to swap inside and outside.
• Effect too strong - reduce the masked effect's opacity or its own strength.

Tip: Build selective corrections subtly. A softly feathered mask and a gentle effect are usually invisible; a hard edge and a heavy effect shout "this was fixed in post".