All About Curves - Part 2: Using Alpha channels for Selections and Reselections
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This tutorial covers using alpha channels to make selections and reselections. Alpha channels are a useful and time saving tool for any selection, especially irregular shapes and complex selections with many colors or with antialiased edges.

What are Alpha channels?

Alpha channels are simply selected areas stored with the image in .psp format. When anything that is outlined with a marquee (the marching ants) is added to an image, it can be saved to an alpha channel and reused.

Why use Alpha channels?

When selections are saved to alpha channels, they are very easy to reuse, giving more precise results than using the magic wand. They are especially useful on irregular shapes, complex selections, and any selection that has had antialias applied to smooth the edges.

Once an alpha channel is created for a selection, as long as the image it is saved with is open, that selection will be available to use on any other image that is open. So you can create complex shapes in one image and reuse them in another.

Let's take a look at the difference between an area reselected with the magic wand, and one reselected with a saved alpha channel. In the first image, which is the fancy letter P in Pixel's Paintshop, the letter has been reselected using the magic wand. You can see that not all the smooth edge pixels are selected, because the letter has antialiased pixels making up the curly-que part of the letter. In the second image, the selection has been redone using an alpha channel. You can see that the exact shape of the letter is reselected.

    

How to save to an Alpha Channel

You can save to an alpha channel any time there is a marquee (the marching ants) surrounding a selection. I personally save almost everything to alpha channels, especially when applying fonts. It makes it much easier to change the color of a letter, or reselect it to apply a BladePro effect.

To save a selection to an alpha channel, on the menu choose Selections | Save to Alpha Channel. A control box will open asking you which image to store the selection to, and what to name the alpha channel.



    

How to reuse an Alpha Channel

You can use any alpha channel that is stored with any open image. If the letter P is an alpha channel in image1.psp , as long as image1.psp is open, the selection can be used in another image. To reuse a selection from an alpha channel, on the menu choose Selections | Load From Alpha Channel. A control box will open asking you which image to get the alpha channel from, and what the name the alpha channel is.

That's it. Alpha Channels are your best friend.