Alpha 3D and Vector Displacement meshes
Grow complex shapes!
Alpha textures are grayscale images used with brushes to affect how they displace the surface geometry of a model. Alpha 3D represents an evolution of this system. This format allows ZBrush to use a 3D shape to deform the model when applying a stroke. This gives better results when it comes to reproducing an existing shape, such as making horns grow from a dragon’s skull.
Regular 2D alphas are very convenient when it comes to producing fine details like skin pores, small scars, or fabric patterns. However, when using these 2D alphas to create major shapes they are restricted by vertical elevation and cannot support overhangs or undercuts. The Alpha 3D feature does not have these restrictions as a 3D alpha will deform the underlying surface of model by using a stored mesh. The Alpha 3D system uses an internal, Vector Displacement Mesh (VDM).
The only restriction will be the density of the polygons needed to reproduce the brush’s VDM shape. If you are working with a low resolution mesh, your model may not have enough polygons to deform to flawlessly rebuild the shape stored in the brush.
To learn more about Alpah 3D and Vector Displacement Meshes explore the pages below: