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How to Create the Opacity Map of an Image in Photoshop

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The time when you need to know how to create the opacity map of an image -also known as Alpha Channel- comes when trying to insert images of trees, plants and people inside AutoCAD, 3ds Max, Blender and Maya, or any other 3D software.

However, this process is pretty easy if you have Photoshop at hand. Just follow my instructions in this tutorial and enjoy.

Step 1. Open up Photoshop and open your transparent tree. (In this example we are working with a transparent image of a tree in png format).

We need to create 3 layers above the Layer 0 of the png image. Shift+Ctrl+N to create a new layer. Name it Layer 1 and then create two more layers. The Layers Panel must be looking like the image below (Image 1):

How to Create the Opacity Map of an Image

Step 2. In the Tools Bar, click in the icon for Default Foreground and Background Colors (Image 2), or simply press D.

Step 3. Make sure Layer 3 is selected. Ctrl+A to select the whole image. Type M, right click in the image, and select Fill. In this window, Background Color must be selected in Contents. Click OK. Now the whole layer is white. Ctrl+D to deselect all.

Step 4. Select Layer 2. Ctrl+A to select the whole image. Type M, right click in the image and select Fill. This time Foreground Color must be selected in the Contents section. Click OK. Now the whole layer is black. Ctrl+D to deselect all.

Step 5. In the Layers Panel, select Layer 0 (the layer of the png image). Position the cursor in the layer’s thumbnail, Ctrl+Click to select the whole content of the layer. Now select Layer 1. Type M, right click in the image, and select Fill. Select Background Color and click OK. Ctrl+D to deselect all.

Step 6. In the Layers Panel, click and drag Layer 2 below Layer 1. And click and drag Layer 3 below Layer 0. Turn Off Layer 1 and Layer 2.

After these steps, the Layers Panel must be looking like the image below (Image 3). You must see the tree in a white background.

How to Create the Opacity Map of an Image

Step 7. Click in Layer > Flatten Image > Discard Hidden Layers? Click OK. Now click in File > Save As, and save it as a JPEG using this name: MyTree-Normal. In the JPEG Options, give it a quality of 12 and click OK.

Step 8. To go back in time and get the layers back to the stack, press F9 key to open the History. Or go to Window > History. And click in the last action before Flatten Image, in my case, Layer Order, according to the image below (Image 4).

How to Create the Opacity Map of an Image

Step 9. Click in the Layers Panel and turn Off Layer 0 and Layer 3. Turn On Layer 1 and Layer 2. In this moment you must see a white tree in a black background (like Image 5, below).

How to Create the Opacity Map of an Image

Click in Layer > Flatten Image > Discard Hidden Layers? Click OK.

Click in File > Save As, and save it as a JPEG using this name: MyTree-Opacity. Give it a quality of 12.

Close the image. That’s all.

Now you know how to create the opacity map of an image using Adobe Photoshop. It’s time to insert your images of trees and plants in AutoCAD 3D.

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