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Chapter 8. Compositing Images > Working with Alpha Channels

Working with Alpha Channels

Image-editing programs such as Photoshop and Fireworks allow you to create an image against a “transparent” background (Figure 8.33). In reality, there’s no such thing as a transparent background—the pixels in a bitmapped image are always opaque. What these programs really do is create a mask at the same time you create your image, and then use this mask to give the illusion of transparency when the image is displayed on your screen (Figure 8.34).

Figure 8.33. Here, this image of a smokestack appears on what looks like a transparent background in Photoshop.



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