Realtime NPR with Cell Shading and Outline Look

ZBrush allows you to work with real-time materials that offer the ability to create and work with a cell shading effect. With simple settings and curves manipulation, you can produce a two or three tone shading for your regular materials and even add Flat Shadows on top of that (see the next chapter).

First of all, you need to load a standard material, since the system is incompatible with MatCap materials. SkinShade4 is a good option for this. Then open the Material >> Modifier sub-palette and click on the Diffuse Curve to open it.

This is where the magic happens. If you click and drag the center dot out of the editor and (without releasing) back into the curve editor again the dot will be transformed from a curve transition to an angle transition.

Then click on the curve to add two extra dots. Follow the same steps as before to change these new dots into angle transitions as well. Simply position them within the curve editor to create a step pattern as shown in the screenshot below.

As you will notice, the diffuse color is now composed of two parts represented by the two vertical lines in the curve editor. If you add more steps, you will add more steps in your shading.
Now create a similar stairstep with the Specular curve located below the Diffuse curve. You can also use the Copy/Paste functions located in the Curve editors.

At this stage you can tweak the curves to refine the effect. Changing the vertical lines to slants will make the transition between each step less sharply defined. Changing the Focal Shift and the Strength sliders in the curve editor will alter the contrast or intensity in the different steps.

Finally, you can add an outline to have a better perception of the silhouette and parts of your model by going in the Mixer sub-palette, located below the Material Modifiers. In this sub-palette you will find the Outline slider. Increasing its value and tweaking its depth value will create a great outline effect. If you want to change the outline color, simply return to the Material Modifiers and click on the Cavity color patch to change it from black to the color of your choice.

For the final touch, don’t forget to change your shadows to Flat and then perform a BPR render. This will give a more refined result that is still very close to the real-time display.