An Alpha is a grayscale intensity map. It can be used to represent intensity, masking, and similar things. For example, bump maps and displacement maps (both in ZBrush and in other programs) are both alphas; the gray intensity represents the height or depth of the bump or displacement.
In ZBrush, alphas are used for much more than just bump or displacement maps. They can affect masking (which parts of an model or painting you work with), brush appearance, how colors, or materials are laid down, and the shape of sculpts. And probably a few other things I can’t think of right now.
In addition, you can make your own alphas, and also turn alphas into other tools, such as Stencils (which are masking tools that offer a different, and powerful, set of capabilities).
Below, we describe the most common ways of obtaining and using alphas. We also give links to pages which describe material significantly related to alphas.
- Many of the standard drawing tools use alphas to control their shape. This affects the depth of pixols on the canvas.
- Alphas may be used with 3D sculpting brushes to affect the geometry of 3D models.
- Alphas are the means by which displacement and bump maps are exported from ZBrush.
ZBrush comes with a large selection of useful alphas, which can be selected from the Alpha Palette or from the pop-up palette that appears after clicking the large Current Alpha thumbnail.
You can of course load your own images for use as alphas using the Load Alpha button in the Alpha palette. Colored images will be converted to grayscale.
You may find it more convenient to simply paint a pattern on the screen, and then use the GrabDoc control to convert it into an alpha. The depth of the scene you created will be converted to the alpha (color will be ignored). Since ZBrush supports 16-bit depths, you will get a true 16-bit alpha.