Sculpting - Blender Foundations: The Essential Guide to Learning Blender 2.6 - page 240

Baking to a Normal Map
Once you have sculpted your details, you have to get them back onto the original model. Just using the
sculpted form is possible, but if you're over the 2 million polygon range, your renders are going to be
unnecessarily lengthy. You can tell Blender to store the high-resolution detail in a kind of bump image
called a normal map . When you use a black-and-white image as a bump map in Blender's texturing
system, the renderer simply says, “If the image is white here, I'll pretend that the surface is this much
further along its normal value.” Bump mapping only encodes for “in” and “out” normal variation. An
actual normal map, though, uses all three image channels (RGB) to encode an actual direction and distance,
generating a much more realistic effect.
To create this type of normal map, save your sculpting work and reopen the original scene file. Use the
Append command (F1) to find the head model in the separate file that was created for sculpting. The
goal is to get the high-resolution head to sit in the exact position as the low-resolution one. To do this,
bring up the N-key properties panel, select the high-resolution head, then Shift select the regular head so
it is active. RMB over the transform controls in the panel for both Translation and Rotation. From the
RMB menu, choose Copy to Selected . This copies the transformation of the regular head to the sculpted
head, putting them in identical locations and orientation.
If you find that things are too slow in the main scene with the high-resolution head brought in, make
sure that the Preview value on the Multires modifier is set to 0. If things are still too slow, change the
display type on the 3D view header to Bounding Box . You'll only see a bunch of boxes that represent
your objects, but the display speed and interface responsiveness will be back to normal.
For the baking process, we need a blank image attached to the low-resolution object and a UV unwrap.
We already have a nice unwrap for our head (the “final” channel that we projection painted into). Select
the low-resolution head, make sure that the “final” UV channel is selected for Render in the Mesh prop-
erties, and add a new image in the UV/Image Editor. It won't hurt to use a 2048 × 2048 pixel image, as
it would be nice to capture all of that detail that has been put into the sculpt.
That's the setup. To actually bake, we do the standard multiple-selection dance that we've done elsewhere
when there is a source and target to be defined. RMB select the high-resolution head (the source), then
Shift-RMB select the low-resolution one (the target), making it active. On the Bake panel in the Render
properties, shown in Figure 8.19 , choose Normals
from the Bake Mode pop-up menu. The standard
method of normal baking is in Tangent space,
which is selectable on the Normal space control.
Finally, enable Selected to Active , which does the
normal comparison between the two objects. Hit
the Bake button, and take a break. It won't take
too long, but it is a render process.
As soon as it's done, use the Save As … command
in the UV/Image Editor to save the baked image. Figure 8.19 The Bake panel.