Page 280 - Enhancing CAD Drawings with Photoshop

4386.book Page 264 Monday, November 15, 2004 3:27 PM

264 CHAPTER 8 ILLUSTRATING ARCHITECTURE

Figure 8.8
Rendering the Shadow
element

Rendering Special Image Channels with MAXScripts
3D programs generate what I’m calling special image channels internally during the process of cal-
culating a rendering. ObjectID, Normal, and Zdepth are examples of special image channels in VIZ;
these will later aid in maintaining pseudo–three-dimensionality and object-selectability in Photo-
shop. You will eventually render these channels as image files and then composite them as channels
in the illustration project.
These channels represent data that separates the objects (ObjectID), determines which way all the
geometrical surfaces in the model are oriented (Normal), and calculates the distance each object is
from the picture plane (Zdepth).
NOTE The Zdepth channel can alternatively be rendered as a render element.

VIZ’s graphics buffer (G-Buffer) stores object numbers that identify nodes to be included in postpro-
cessing effects. In other words, ObjectIDs are just a means to mark certain objects for postprocessing.
Accessing special image channels is an advanced topic in VIZ, so I’ve written a pair of MAXScripts
that automate this process for you. We will assign unique ObjectIDs to every object in the scene with
a MAXScript called ObjectIDAssigner. Then every object will be included on the ObjectID image
channel when we render the scene using a second MAXScript called ChannelRenderer (along with
other channels). Let’s give it a whirl. So that you are aware of what the first MAXScript is automating,
let’s first take a look at object channels as they are stored in the G-Buffer.

1. Click the Tree object in the viewport. Right-click and choose Properties from the transform quad.