How many times have you wanted to duplicate a real-world surface, only to spend hours trying to a good enough quality grayscale image of it that you could then stamp as a bump map? Thanks to ZBrush's depth-enabled canvas, it's actually faster and easier to create your own high-quality alphas, which can be modified on the fly and used in a variety of ways: change the shape of your paint brush, paint through as a stencil, stamp onto portions of your texture, or paint seamlessly to cover wider areas. Skin folds, pock marks, rough bark, wooden shingles, corrugated metal, rust, exotic hides and even dragon scales are possible. ZBrush makes it easy to create any alpha that you might need for your texturing work and thanks to the tilde-scrolling feature, these alphas can be created to tile seamlessly.
In the example above, a scale was quickly sculpted from a Sphere3D object. The Tool>Initialize menu was used to shape a low polygon sphere, which was then converted to a polymesh. Within minutes, the polymesh was reshaped, divided, and sculpted to be a simple reptilian scale.
The scale was then snapshot repeatedly to a 1024x1024 canvas, being careful to stay away from the edges. When the center was filled with scales, the tilde (~) key was pressed and the canvas dragged so that the sides became the new center. This was filled with more scales, and the process was then repeated to fill in the remaining space. The result was a seamlessly-tiling canvas, with depth that could be sampled by pressing Alpha>GrabDoc.
Such an alpha can easily be modified by using the features in the Alpha palette. For example, the AlphaAdjust curve can modify the levels to enhance details, or the Radial Fade (Rf) slider can be used to create a falloff at the edges for texture stamping.
Nearly any alpha imaginable can quicky be created in this manner. For example, the canvas can simply be filled (Ctrl+F) and then a few wrinkles drawn with Zsub active and using the tilde-scrolling technique. Such an alpha might look like this example:
Such an alpha can simply be converted to a texture using Alpha>Make Tx. Projection Master is then used to drop the model to the canvas, and the Deco Brush selected with the TileTexture modifier active. The nice thing about using a texture converted from a seamlessly-tiling alpha is that your brush strokes can follow the contours of the object that you're texturing (such as the spiral, below), which makes it easy to paint believable details for your textures or bump maps.
Another feature that ZBrush offers is the BumpViewerMaterial, which is included with ZBrush 2 in the ZMaterials folder. This material hides any color that you paint and instead displays it as bump. In the example below, the Deco brush was used to paint the scales onto a spiral. The top left shows what you see when the BumpViewerMaterial is used. On the bottom right is the actual grayscale texture that was painted. Obviously, the BumpViewerMaterial makes it a pleasure to paint bump maps, since you can see the real results as you paint your model rather than trying to guess what effect each grayscale value will have.
Hopefully these quick tips will help you tap into the power of ZBrush any time you need a custom alpha or to paint a bump map for your work! In fact, the power of bump maps will become even more apparent once ZMapper has been released. That plugin will allow you to create normal maps for your models by incorporating details that are generated from a bump map -- details that would require a mesh with millions of polygons more than even ZBrush can accomodate as geometry. Stay tuned!