Manipulating Masks

From ZBrush Info

This section addresses how you can create and manipulate masks directly on the screen. You can do the following.

Paint Masks:

You can paint masks on your object directly by holding down the Ctl key while painting on the model. (The stroke must begin on or close to the model.) By default, masked areas show up as dark patches on the model. The following figure illustrates this:

Left: Small masked 'dots' on the model created by holding down Ctl while drawing very short strokes with a small brush.
Right: Masked model after sculpting. Masked areas were not affected by sculpt.

Drag Rectangles Across Part of Your Object

Hold down the Ctl key, click on the canvas outside your object (not too close, either), and drag a rectangle across part of your object. You can see the results below. Note: You need to start the drag outside the object, but you don't need to end it outside the object.

Lasso Parts of an Object to Mask

1. Press Ctl+Shift+M or press Transform:Lasso (identified in the popup help as Transform:Marquee) to toggle into lasso mode.
2. Hold down the Ctl key, click on the canvas outside of your model.
3. Drag out a lasso selection.

Invert an Existing Mask

To invert an existing mask, hold down the Ctl key and click on the canvas outside the model.

Mask before and after being inverted with Ctl-click on the canvas.

Blur a Mask

Ctl-click on a masked area to blur the mask. This will 'spread the mask out' further across the object, while decreasing its intensity.

Unmask an Area

You can 'unpaint' a previously masked area, by holding down Ctl+Alt and painting onto the model.

In this figure, the inverted mask has been taken from the previous figure, and the 'border' of the model has been unmasked using Ctl+Alt-paint.

Clear a Mask

Hold down the Ctl key and drag on the canvas outside the model. Any visible amount of dragging will do.

Create a Mask Using Topology

This masking method is discussed more thoroughly in the Transpose page, which is where the topological masking is functional. Basically, when in transpose mode, you can Ctrl-drag along the surface of a model, to have a mask dragged out across the surface, following the topology of the model. On models with typical topology, this gives an extremely fast, easy way to mask out limbs, tentacles, branches, and other extrusions.