Distributing Information Across Channels
From ZBrush Info
If you need to define options for your own exporter configuration, you’ll probably need to understand some things about the TIFF file format, since the Displacement Exporter(DE) exports all of its displacement maps as TIFF files. If you are working with a predefined configuration, or can find a Quick Code that meets your needs, there’s no need to read this section.
A standard TIFF file can contains anywhere from 1 to 5 channels, with 1 (for grayscale images) or 3 (for color images) probably the most common. DE exports TIFF files with either 1 or 3 channels.
In addition, each channel in a TIFF file may be 8 bits, 16 bits, or 32 bits. A 16 bit alpha displacement (as exported by ZBrush) requires 16 bits of data per point. The most straightforward way of achieving this would be to use a TIFF file containing a single channel, with that channel having 16 bits of resolution.
There are other ways of achieving the same effect. All that is necessary is that the TIFF file be able to store 16 bits of information for each point in the image. For example, a TIFF color image file usually has three channels of information, with each channel storing 8 bits of color data. This means that each point in the image has a total of 24 bits of data associated with it. We only need 16 bits of information per point to store a ZBrush displacement map, so we can still use this image file format; for example, 8 bits of information could be stored in the red channel, 8 bits stored in the green channel (for a total of 16 bits), and the blue channel could be ignored completely. Attempting to view such a file using a color viewer would result in an onscreen image the would probably look like an insane artist had painted a picture using just Day-Glo colors, but that’s just because the viewing program would be trying to interpret the data at each point as a color, when it is in fact meant to be interpreted as a grayscale intensity stored in an odd manner.
Doing something like this means that, in effect, one “conceptual” channel of information is spread across more than one actual channels in the file.
This is important because programs importing displacement maps in TIFF file format may expect that data to be arranged in different formats within the file. The reasons for this are usually historical. In the past, not all variants of TIFF file formats may have been readable by all programs3, so improvisations like encoding a 16 bit grayscale image into a 24 bit color image were used to move data around. Over time, some programs came to expect such workarounds as normal, and since these workarounds became accepted practice, that’s still the way it is today.
