Actually, in ZBrush, you can't render multiple subtools at the same time. To do it, we are going to snapshot each HD subtool on a separate layer, and we will need the help of the Zapplink plugin.
1. Create a new document which will have the size of the final image, place your tool on the document, and switch off the visiblity of the girl, the eyes and lashes Subtool.
2. In ZAppLink, store the position of the tool on the Custom 1 view.
3. Select the Set subtool, which is the bigger one, open the Geometry HD subpalette, and press the Sculpt HD button. The whole model is displayed in HD.
4. Open the Transform Palette, and Snapshot the tool on the layer.
Open the Layer menu and create a new layer.
5. Draw your model on this new layer, and recall it's stored position using the Zapplink Palette.
6. Switch on the visibility of all the subtools.
7. Now, in the Render menu set the Flatten option off.
8. Select a BasicMaterial and set the Specular and Transparency values and the Transparency curve as shown.
8. Paint the Set subtool and the two red balls subtools with this transparent material. The HD model of the set should appear on the underlying layer.
9. Select the girl model, render it in HD.
10. Save your document, and turn Edit Object mode off.
11. Export the Document in Tif or Psd Format.
12. Turn off the Set subtool.
13. In the Alpha menu, grab the document, and save the related alpha.
14. Turn on Set; grab the document again, and save another picture. We will use them as masks later in Photoshop.
Rendering the Shadows:
To have a better control over the final image, we are going to need to render the shadows on separate layers.
To do it, select a new BasicMaterial, and set the Ambient, Diffuse, Diffuse curve and Specular parameters as shown. The picture should look completely white, but don't worry. This kind of material doesn't have any shading, but will catch the shadows.
To use the Light menu, click on a light to select it, and click again to turn it on or off. The placement sphere in the upper left of the palette shows where the currently selected light is placed, and also shows the combined effect of all lights currently turned on. Drag the small yellow rectangle to change the placement of the current light; click it to toggle it from a front light to a backlight, or vice versa.
On this Document, two lights will be enough to get nice shadows; one front light and one backlight. Switch on the ZMode only for the key light.
When you're fully satisfied with the result, render each light separately, and export the document as .tif or .psd. Here are the five pictures you should have saved.
Compositing and Final Touches:
In Photoshop group the shadow layers together, and set the Blending mode of this group to multiply. Use the Alpha picture of the girl model to create a mask so that the backlight shadow layer doesn’t affect the Set. Then, give to the Key shadow layer a parma tint, and to the backlight layer a blue tint. The drops of water are simply painted in Photoshop. Set the Layer Style to add Drop shadow and Inner Bevel effects. Use the second alpha picture to mask the background, and to composite the sky.
