Preview: OS X's Secret Weapon Image Editor

Preview is the default PDF and image viewer in OS X, but many users never get further than that. While Preview is certainly a great app for browsing images, it’s also got a lot of options for editing and refining images, too.

We’ll take a look at some of the often overlooked tools inside Preview and walk through each of them individually. By the time we’re done, you’ll know Preview inside and out and have a new respect for this neglected image editor.

Preview as Image Editor

Preview has some pretty great image editing tools, but first you need to get at them. Most of them are available in the Tools menu, but you can also toggle the Edit Toolbar on and off by clicking the pen icon in Preview’s main toolbar.

Create New Image From Clipboard

If you want to save and edit an image from the internet, you don’t actually have to save it at all. Just copy the image to your clipboard and then choose File > New From Clipboard. Preview will create a new image from your clipboard contents.

This doesn’t just work for images copied in your browser, though. Pretty much any image or image selection will work. Select an area in one Preview image, copy it to the clipboard, and create a second Preview image with just the selection area.

Select and Crop

Rectangular Selection

The Rectangular Selection tool is your default in Preview, so if you haven’t started doing anything else, you can drag your cursor around on your image to select your crop area. If you’ve used other tools already, the Rectangular Selection tool is available in the Tools menu (Tools > Rectangular Selection) or by clicking the Selection Tools icon.

Drag your cursor so that the entire area to be included in the final image is incorporated in the selection. Fine tune your selection by grabbing the corners or edges of your selection and growing or shrinking the crop area. When you’ve got everything just right, click on the Crop to Selection icon in the toolbar or select Crop from the menu (Tools > Crop). Everything outside of the selection area will be deleted from your image.

Elliptical Selection

Preview doesn’t just select rectangular and square areas, though; you can crop a round selection. Click on the Selection Tools icon in the toolbar, and choose Elliptical Selection. When you start dragging your cursor this time, you’ll create a round shape. This selection can be cropped in the same way as a rectangular selection, using the Crop to Selection tool. 

Lasso Selection and Smart Lasso

Lasso Selection will allow you to trace an irregular shape. This is handy if you need to crop around any of the myriad objects in our world that aren’t perfect rectangles or ovals and may find their way into your images. Even better is the Smart Lasso, which sort of cleans up a freehand selection. Select your odd-shaped object with Smart Lasso, and Preview will do its best to figure out what you actually intended to select.

Instant Alpha

Use Instant Alpha to select a conspicuous foreground or background object or when you want to select among easily distinguishable colors. With Instant Alpha selected, drag the cursor along a section of your image. Your image will begin to fill up with red, but you’ll notice the red fill will follow the lines of your foreground or background. Everything highlighted red becomes part of your selection. You can either delete your selection or crop around it.

Invert Selection

If you’ve selected an area other than what you want to preserve when you crop your image, for instance if you selected the image’s background but want to keep the foreground, remember you’ll lose everything outside of the selection area when you crop. To save what’s outside the selection instead, you can invert the selection (Edit > Invert Selection).

Resize

After cropping your image, it may still be too large. To get it to the correct dimensions, click the Adjust Size tool in the Edit Toolbar or from the Tools Menu (Tools > Adjust Size).

Rather than slicing off a bit of your image to fit a set of dimensions, Adjust Size will scale your entire image up or down to fit the new height and width. If you have specific dimensions in mind, select Custom from the drop-down; otherwise, you can choose one of the presets.

Set your width or height and whether the image should scale proportionally, that is, whether it should keep the same width to height ratio. You can also change your resolution here, too.

When you’re all set, click OK, and your image will be resized according to your settings.

Rotate

Often a photograph won’t be oriented properly once it’s been imported from another device. That’s okay, because Preview will take care of that. Use the Rotate tool, located next to the Show Edit Toolbar icon, to spin your image around. You can also find rotate tools in the Tools menu (Tools > Rotate Left)/(Tools > Rotate Right).

If that’s not good enough, you can flip your image along the horizontal or vertical axes (Tools > Flip Horizontal)/(Tools > Flip Vertical). This is a great one to use if you take a selfie and are surprised when your mirror image flips, making your perfect pose look like a Frankenphoto. Or, you know, if you have a less narcissistic reason to flip your image, that works, too.

Adjust Color

You can change how your image looks by adjusting colors, such as your exposure, brightness, and contrast. Open the Adjust Color tools by clicking the prism icon in the Edit Toolbar or in the Tools menu (Tools > Adjust Colors).

Adjust your image’s exposure, probably more useful on a photo, or oversaturate the colors in your image. Preview also allows you to control your photo’s tint and warmth, and you can even make everything look old timey with the sepia slider.

There are really only a handful of options to fiddle with here, so if you’re used to having full control over your image in a more powerful editor, Preview’s controls may feel a bit ham-handed. That doesn’t mean there isn’t still a lot you can do with Preview, but you should manage your expectations when using the Adjust Color tools.

Annotations

Shapes

For my money, Preview really shines when it comes to creating useful and attractive annotations. Underline or draw circles and squares around important elements. Use arrows to highlight relevant components of your image. All of the annotation tools are located on the far left of the Edit Toolbar or in Tools menu (Tools > Annotations).

To create a new annotation object, select the circle, square, or arrow icon, and drag your cursor inside your image. Try to get it to about the size and position you want, but since you can continue to edit your object later, there’s no need to be exact. Adjust your object’s size by grabbing its edges. Select and drag your object to move it around your image.

Change the border or line color of your object by clicking the Colors tool. You can also choose a fill color as well. If you don’t like the default colors, select Other, and use the color picking options.

Set line and border thickness by clicking the Line Attributes tool. After selecting thickness, you can also choose whether you want a solid or dashed line. If you’re creating arrows, choose single- or double-pointed.

Text

To insert text into your image, select the Text tool icon, and draw a rectangle. Don’t worry if it’s not exactly the right size yet, because you’ll change that later. If your text box isn’t big enough, keep typing, and when you resize the box, all of your text that appeared cut off will be there.

Click the Show Fonts tool to change your text’s font, color, and styling. Now’s the time, once you’ve got your text looking exactly how you want, to finetune your text box’s size. Because you’ve likely changed your font’s size, it’s best to wait until everything else is set before you make final adjustments to the text box.

When you’re done, click on your text and drag your text box around your image to place it just where you’d like it to go.

Speech and Thought Bubbles

You can combine annotation shapes and text boxes, using text to call out specific aspects of your images. Preview goes a step further and gives you built-in speech and thought bubbles, too. Creating these shapes is similar to creating annotation shapes, except that they are also ready-made text boxes.

Select the Speech Bubble or Thought Bubble tool and click and drag to create a shape, as when creating an annotation. Again, don’t worry about the exact size of your bubble, as you will adjust this later. Begin typing inside your bubble, and select the Show Fonts tool to customize your text.

When you’ve finished with your text, drag the corners of your bubble to get it to just the right size and shape. Click anywhere in your bubble to move it around your image.

Export

The ability to export images to different formats is so useful, I hesitate to bury it at the bottom of the tutorial, but I’m trying to run these Preview features through in the order you might use them, and Export would come last. Similar to saving a document, exporting is what you do when you’re done with an image. You’re so done, in fact, you’re even done with its original format.

If you have thumbnails of your images visible along the left side of Preview, you can right-click on your image and select Export As..., but your thumbnails will likely only be there if you have multiple images open. With a single image open in Preview, you can usually only Export from the File menu (File > Export...).

You’ll get something that looks a lot like a Save dialog. At the top, notice that the field where you change the file’s name is labeled Export As. In the bottom third of the dialog are your file format options. Choose a format and quality (if applicable), and whether you want to hide the file’s extension.

When you’re done, click Save. Your original image will remain open in Preview with its original extension. If you’ve made unsaved changes to your image and would like to preserve them in the original file format, you’ll need to save that file, too.

Browse Version History

You and I both know you’re perfect, but let’s say for the sake of argument that you made a mistake somewhere along the way. You did something bad to an image, and then you saved it. There’s no going back, right? Wrong. On Lion and Mountain Lion, Preview keeps a version history for all images you edit, sort of like Time Machine.

Click on the name of your image at the top of the Preview window, and you’ll get some basic file options. Select Browse All Versions, and you’ll be transported via wormhole to your image’s past. Or Preview just open’s up your file’s version history, whatever.

Snapshots of your image will be displayed, with the newest first. Scan backwards until you find the one you need, and click Restore. The older image will replace the new, though, so if you want to keep both, you should copy one into a new Preview file.

Lock

When you’re done with an image and absolutely don’t want it to be edited anymore, Preview will lock it for you. A locked file can’t be edited further. Well, okay, I’m going to level with you, there’s nothing that’s really going to stop you from editing a locked image file, but Preview will warn you before letting you move forward that you’re trying to edit a locked file.

To lock a file, click on the filename at the top of the Preview window, and select Lock. That’s really all there is to it. To unlock the file, click the filename again, and select Unlock. If you try to edit your image while it’s locked, Preview will ask you to either duplicate the file or unlock it.

Final Thoughts

Preview can be easily overlooked as nothing more than OS X’s default image and PDF viewer. Hopefully you learned there’s a lot more you can do with Preview, including some pretty useful image editing. For more on how to get the most out of Preview, check out our tips on combining PDFs and digitally inserting your signature into documents.

Is Preview already one of your go to apps? Do you have a tip we missed? Let us know in the comments!