ZBrush Specular Map Painting Tutorial
Hello everyone, I have decided to take the initiative and create a small tutorial on visualising specular values on a ZBrush mesh. Mudbox 2009 will have this, too, but I want to demonstrate how to see different specular values that will look proper in a renderer, such as Mental Ray.
First of all, I'd like you all to meet Mr. Frogman, who has kindly volunteered to help out (and I'm hoping he forgives me for cutting off his body).
The purpose of this tutorial is to help people who have asked on ZBrushcentral.com how to actually see the specular map in real time - well, the values anyway. As part of my pre-ZBrush workflow I had to paint in Photoshop in a messy way, save, and then look at the model in my 3D programme by rendering. But the way I'm going to show you here is a little trick that I've learned, using a custom material that I'll be happy to share with you. I'm assuming you're all already familiar with the ZBrush interface, so let's get started.
First, import an OBJ or load an existing SubTool and draw it on the canvas. Then make it live by pressing Edit, or the T key (Fig.01).
Change the current material from MatCap Red Wax to MatCap Metal02 (Fig.02a - b).
Fill the object with a low grey colour; in my case I chose the values 64, 64, 64, which is 25% grey in Photoshop - a nice slippery grey perfectly suited to Mr. Frogman (note: you can also Mask by Cavity first and then fill, but I find it's better to do all of this from a Cavity Map and then blend the image into the specular map) (Fig.03).
You should see the model in the viewport. Now just paint with a low RGB strength (I usually use values between 1 and 5 to get a neat gradual tone, and white) and you'll see the model's skin look as if it's specular in different spots (Fig.04). Don't forget to turn off ZAdd before you do this.
Surely, the Metal MatCap does not necessarily show the shininess, but you'll notice that dark areas will have no gloss when you rotate the model, similar to metal when it rusts. If you change the render view to flat, you will actually see how the spec map will look in Photoshop (Fig.05).
Now, export your specular map by creating a texture first from the colour and apply that image to a model in your 3D package - and voila! (Fig.06a - b) Note: don't forget to set the RGB strength back to 100.
In my case, I'm using XSI; you can see the advantages of creating seamless specular maps with no fuss (Fig.07). You can add other details like the cavity map to the existing texture to enhance it, and it also eliminates the guesswork of how the map might look.
Thank you for reading and Happy ZBrushing!