Issues in Exporting Alphas for Displacement

From ZBrush Info

Displacement maps are simple in concept, but subject to various technical considerations when moving them between applications; this is what the DE is designed to address. Below are the common challenges that can arise when moving a displacement map from one application to another:

• Mapping of alpha intensities to measurements in the target program’s world coordinate system. Displacement maps simply represent intensities, with no units attached. Should a value of white (the highest intensity) cause a displacement of a centimeter, an inch, a foot, or some other measurement? For that matter, should it cause a displacement into the surface, or out from it?
• Displacement map grayscale resolution. Many alphas store 8 bits of data per pixel, meaning that they can represent only 256 distinct shades of gray, from black to white. ZBrush can store 16 bits of data per pixel in an alpha, which means alphas can have 65,536 distinct shades of gray. In practical terms, 16 bit displacement maps can produce much more realistic displacement surfaces when they are applied, particularly if the displacements are relatively large in the absolute coordinates of the global coordinate system where the map is being used.

On the other hand, some programs may only be able to use 8 bit displacement maps, so provision must be made for converting a ZBrush 16 bit alpha into an 8 bit alpha for use by such programs.

• File formats. Alphas are images, and so are moved between different programs using some sort of image file format. However, many types of standard image file formats do not offer a format that can easily deal with 16 bit alphas. The displacement exporter exports all of its files in TIFF format, which is a very flexible file format well suited to this type of application. However, the TIFF format is so flexible that different programs may expect alphas to be represented in different ways even within TIFF files, and so the displacement exporter allows you to define exactly how the data elements of the displacement alpha are stored into the TIFF file. See the section on the TIFF format. If none of the DE predefined configurations is suitable for your use, it’s still likely that most of the option settings you’ll need to make will be quite simple. Even better, other ZBrush users or your own technical support people may well define a necessary configuration, and then simply supply a Quick Code you can enter to get exactly the configuration you need for a specific task.