Figure 7.14

The Material/Map Browser dialog box

6. Click the Assign Material To Selection button on the Material Editor toolbar. Notice the white triangular corner tabs that appear in each corner of the material sample slot; these indicate the material is hot, or instanced in the scene.

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7. Do a quick render (press Shift+Q). The RFW appears, displaying the framing object in red. Click the Display Alpha Channel button on the RFW toolbar. The grayscale alpha channel displays, showing the boundaries of this object. Notice that the RFW indicates this is an RGB Alpha image, meaning there are a total of four channels held in the RFW (Red, Green, Blue, and Alpha), sometimes called RGBA.


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8. Click the Save Bitmap button on the RFW toolbar. Navigate to the folder on your hard drive where you want to save the compositing renderings (I recommend making a folder called Output); click the Save As Type drop-down list box and select Targa Image File. Type Framing.tga in the File Name text box and click Save.

NOTE See Chapter 1 for a discussion of why RGBA images have 32 bits per pixel.

9. The Targa Image Control dialog box appears. Click the 32 Bits-Per-Pixel radio button. Check Compress for a smaller file size. Also, check Pre-Multiplied Alpha before clicking OK. Close the RFW.

WARNING The alpha channel must be premultiplied for efficient compositing in Photoshop;

otherwise, transparency and anti-aliasing around the object boundaries are thrown off.

Congratulations, you have successfully rendered your first compositing image! We will repeat the object rendering process once more so you get some practice performing these steps manually.

10. Press Ctrl+Z to undo. This is an essential step in the object-rendering work flow! Undo doesn't count for the steps you performed in the RFW; in this case, it undoes the material assignment from step 6. The objects return to their original materials, and the white triangular corner tabs that appear in each corner of the Matte/Shadow sample slot disappear, meaning the material is now cold (or unused in the scene).

11. In the Selection Floater dialog box, click the next object (in this case, Glass Curved). Click Invert, and then click Select.

12. In the Material Editor dialog box, click Assign Material To Selection.

13. Press Shift+Q to do another quick render.

14. Click Save Bitmap in the RFW. Save the file in the same folder you used in step 8. Type Glass Curved.tga in the File Name text box and click OK.

WARNING Always use the same filename as object name to avoid confusion.

15. Click OK in the Targa Image Control dialog box to use the same settings as you did in step 9.

16. Close the RFW if it's in your way, and remember to undo once and only once; press Ctrl+Z to do this.

At this point you could repeat steps 11 through 16 for each object in the scene. Because this scene has only nine objects, this wouldn't take long. Feel free to do this to practice the object-rendering process until you understand why you are performing the steps—but the next section will show you why you don't have to do all the work.

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