Editing and annotating images with Preview

About selection tools

You don’t have to use a rectangular selection tool, however. If you’ve exposed the toolbar, you’ll see five selection tools listed along the top-right of the toolbar: Rectangle, Elliptical, Lasso, Smart Lasso, and Instant Alpha. Elliptical is straightforward—you use this to create an oval or circular selection. (If you wish to force a perfect circle, hold down the Shift key while making your selection.) The other three selection tools require a bit more explanation.

A Lasso selection lets you draw a selection that exactly matches the contours of the object that you wish to select, much as you might trace around the edges of a magazine’s picture with a pencil or pen. But a Lasso selection isn’t complete until the two ends meet; you must end your selection where you began it.

Making a selection in this way can be challenging because a mouse or trackpad isn’t exactly a precision device. For this reason, Preview includes the other two selection tools—Smart Lasso and Instant Alpha.

When you choose Smart Lasso Preview presents you with a very broad drawing tool. The idea is to “paint” around the edge of the area that you want to select. Preview will then decide what you’re trying to select based on detectable edges. For instance, if you have an image of a tree against a blue sky and you outline the edges of the tree, there’s a good chance that the selection will include all of the tree but none of the sky. You can then crop or copy the selection.

The Smart Lasso permits you to be a bit sloppy with your selection.

Instant Alpha is even more clever. Again, Preview tries to guess what you mean to select, but this time it bases its assessment on nearby contiguous colors. For instance, suppose that I have an image of the Apple logo—the gray version—on a red background. If I click the Instant Alpha selection tool, click in the middle of that logo, and drag gradually to the right, increasing amounts of that logo will turn red (based on how close they are to the color I initially clicked) indicating that they’re selected. I can then crop the image so that only the logo shows. Or, I can copy it and choose File > New From Clipboard to place the selection in a new PNG document.

Adjusting exposure, color, and size

Although Preview has nowhere near the editing power of iPhoto, Aperture, or Photoshop, it does let you manipulate your images in important ways. The means for doing so are the Adjust Color and Adjust Size commands found in the Tools menu. (You’ll find shortcuts to these commands in the Edit toolbar.)

When you choose Adjust Color, you’ll see a palette similar to iPhoto’s editing pane, with controls for Exposure, Contrast, Highlights, Shadows, Saturation, Temperature, Tint, Sepia, and Sharpness, as well as Auto Levels and Reset All buttons. Someday we’ll talk in depth about adjusting images with such controls, but today is not that day. Play with the sliders, and you’ll get an idea of what they do.

It isn't Photoshop, but Preview does have some rudimentary image adjustment tools.

Although you can reduce a file’s size by cropping it, occasionally you’ll want to keep every bit of the image but make the image smaller. That’s the purpose of the Adjust Size command. When you invoke it, a sheet appears where you can choose a new size for the currently active image. You can do this by entering values in the Width and Height fields measured in pixels, percent, inches, centimeters, millimeters, or points; or you can click the Fit Into pop-up menu and select a preset dimension (1024 by 768, for example). When you click the OK button, the image will be resized.

If you increase the size of your image (especially if you do it by a lot), the image is likely to become jagged. This happens because the image’s elements swell up and become blockier. So, while you can get away with small size increases, beware of taking giant steps.

About annotations

Finally, you can harken back to your grammar school days by doodling all over someone else’s work through the use of annotations. Preview lets you annotate images in several ways, as evidenced by these tools in the Edit toolbar—Rectangle, Oval, Line, Arrow, Text, Speech Bubble, and Thought Bubble. Just select the tool you want to use and drag it over your image. Once you do, the annotation will be selected and you can drag it to a new position. You can also change its shape by dragging one of its handles.

Annotations let you point out an image's important elements.

Tiny tip: The Speech and Thought bubble’s arrow (where the words apply) appears where you first click when you drag to create the bubble. So if you want it to point down and to the left—indicating that these words are coming from Cousin Jo-Jo’s lips rather than from Aunt Miffy’s—click with the cursor on Jo-Jo’s mouth and then drag up and to the right.

From the Colors menu to the right of these tools, you can choose a color for your annotation (and this affects both its outline and any text it may contain). You can increase or decrease its line width from the Line Attributes menu to the right of the Colors menu. And if you’d like to choose a different font or font size for annotations that contain text, click the Show Fonts button in the toolbar or choose Tools > Show Fonts (Command-T).

Before we close our textbooks, I’ll end with this annotations tip. You’ve slathered an image with annotations: Poor Cousin Jo-Jo has purple ovals covering his eyes, an arrow through his head, and a thought bubble that reads “I am STOOPID!!!” But in the tranquility of sober and mature reflection, you now regret these additions and would like to remove them.

To avoid the penance of selecting and deleting each one, choose Tools > Show Inspector (Command-I). A small Inspector window will appear and, with luck, will show you a list of the annotations you’ve added. (Select the Annotations tab in this window if you don’t see them.) To remove all of the annotations, press Command-A and then press the Mac’s Delete button. At once they’ll disappear. Alternatively you can press and hold the Command key and then select just the annotations that you wish to remove. As you select an annotation in the list, its drag handles will appear so you can see which annotation you’re dealing with.

Next week: Preview and PDFs.

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