Saving the Extraction as an Alpha Channel

Now that you are nearing the end of the tutorial, it is time to create an alpha channel so that you can use the tree as entourage in 3D programs. (You will use the alpha channel in the "Entourage in Autodesk VIZ" section later in this chapter.)

Use the Calculations dialog box to save the image's transparent areas as an alpha channel, as I described earlier. For specific instructions on how to do that for this particular image, follow these steps:

1. Choose Image > Calculations to open the Calculations dialog box. Select Transparency from the Channel drop-down in the Source 1 group. If you leave everything else with the default settings as shown in Figure 4.24, you can click OK to create the alpha channel.

Figure 4.24

Calculating an alpha channel from transparency

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Source l: | PlumTree2.psd

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Layer: j Merged

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Channel: :S20SiEISSWEMI

U ^ F Invert;

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Source 2: J PlumTree2,psd

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Layer: | Levels 1

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Channel: | Layer Mask

r Invert

Blending: | Mdtply jj

Ooaoty: j 100 %

F Mask...

Result: | fstew channel

2. Figure 4.25 shows the grayscale alpha channel image that was generated in the previous step. This image will tell 3D programs where to make the entourage object opaque (white), translucent (shades of gray), or transparent (black). To return the color image, click the Channels palette and click the RGB channel.

Figure 4.25

The alpha channel image

Figure 4.25

The alpha channel image

3. To automatically crop the image, choose Image > Trim. In the Trim dialog box, click the Transparent Pixels radio button and click OK.

4. Rename Layer 0 to PlumTree so that it will be identified properly when you drag this layer into other Photoshop projects.

5. If you plan to use this image in your own work, now is a good time to save it as a native Photoshop file so that its adjustment layers and channels are preserved for future editing. Save the file as PlumTreeEntourage.psd. If you're going to continue working through the following section, you can leave this file open for now.

TIP You can use this tree in an autumn scene by tweaking the Hue/Saturation adjustment layer in the Photoshop file to make yellow or orange leaves.

To prepare the entourage for 3D programs, it is best to save in a flattened format that supports alpha channels to save memory in the 3D program.

6. Return to the Layers palette and turn the Backdrop layer back on. Then flatten the image (choose Layers > Flatten Image, or click the Layers palette menu and choose Flatten Image).

7. Save the image as P1umTreeEntourage.tif. Be sure to leave Alpha Channels checked in the Save As dialog box. In the TIFF Options dialog box, select LZW in the Compression Group, and for the byte order, select the platform on which you are working. Close this file after saving.

Figure 4.26 shows the final image. A version of this image is included in the color section.

Figure 4.26

The plum tree saved for use as entourage

Figure 4.26 shows the final image. A version of this image is included in the color section.

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