The previous section explained how to resize the view of your image as it appears on your monitor. But sometimes you need to change the size of your actual image, and that's what this section is about.
Resizing your photo brings you up against a pretty tough concept in digital imaging: resolution, which measures, in pixels, the amount of detail your image can show. Where it gets confusing is that resolution for printing and for onscreen use (like email and the Web) are quite different.
For example, you need many more pixels to create a good-looking print than you do for a photo that's going to be viewed only onscreen. A photo that's going to print well almost always has too many pixels in it for onscreen display, and as a result, its file size is usually pretty hefty for emailing. So you often need two different copies of your photo for the two different uses. If you want to know more about resolution, a good place to start is www.scantips.com.
This section gives you a brief introduction to both screen and print resolution, especially in terms of what decisions you'll need to make when using the Resize Image dialog box. You'll also learn how to add more canvas (more blank space) around your photos. You'd add canvas to make room for captions below your image, for instance, or when you want to combine two photos.
To get started, open a photo you want to resize and go to Image → Resize → Image Size (Figure 3-17).