Photoshop CS5: The Missing Manual

Basic Channel Stunts

Now that you know what channels are all about, it's time to learn some of the cool things you can do with them. This section covers a few of the most practical channel tricks, but you'll find techniques involving channels strewn throughout this book.

Selecting Objects with Channels

As you learned in Chapter 4, true selection wisdom lies in knowing which tool to start with so you'll have the least fine-tuning to do later. If you have an image with a decent amount of contrast between the object you want to select and its background, you can give channels a spin. All you need to do is create an alpha channel that contains only black-and-white objects, load it as a selection, and then use it to make a layer mask. For example, here's how to use channels to select all the balloons in Figure 5-9 in mere minutes:

1. Open an image that's in RGB mode and has a background you want to get rid of.

   If your image came from a scanner or digital camera, it's already in RGB mode. To check, choose Image→Mode. If necessary, choose RGB Color to switch modes.

2. Find the channel where the objects you want to select look darkest.

   Open your Channels panel and click each channel to find the one where the balloons appear darkest. (You can also cycle through channels by pressing ⌘-3, 4, and 5 [Ctrl+3, 4, 5 on a PC].) The objects will usually be darkest on the blue channel, as is the case here.

   Note

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