Series: The Power of Preview
Six articles that explore the hidden depths of Preview, the Mac’s bundled image and PDF viewer. Most people don’t realize the extent to which it can also edit graphics and manipulate PDFs. Thanks to requests from readers, these articles later served as the basis for the full “Take Control of Preview” book.
Article 1 of 6 in series
The simple facade of OS X’s built-in Preview document and image viewer conceals many powerful features. This week, we show you all the ways you can open files in Preview, including from cameras, scanners, and your Mac’s screen.Show full article
So much criticism has been heaped on the likes of iTunes and Photos that it can be easy to forget the software that Apple gets right — apps that are both simple and powerful. There may be no better example of this than Preview, which has been built into OS X from the beginning.
On the surface, Preview is a simple image and PDF document viewer, although it can also open iWork and Microsoft Office files. Beyond that veneer of simplicity, though, Preview can do so much more. To get a taste of Preview’s power, let’s take a look at how you open images and documents in Preview, starting with the obvious ways and moving on to things you may not know.
Of course, if Preview is your default app for images and PDFs, you can open those files by double-clicking them or selecting them in the Finder and pressing Command-O. Or drag a file to the Preview icon, either in the Finder or in the Dock. Nothing new there.
Slightly more subtle is opening files through Quick Look, which we covered in detail in “OS X Hidden Treasures: Quick Look,” (12 February 2016). In the Finder, select an image or PDF file and press the Space bar or Command-Y to open it in Quick Look. Then click the Open With Preview button at the upper right.
Although Preview is the default app for most image types and for PDFs, it’s possible that another app, like Adobe Reader, has taken over for Preview. If you want to change the default app for a file type, here’s how to do that:
Select a file of the desired type in the Finder.
Choose File > Get Info (or press Command-I) to open the Info window.
Under Open With, choose Preview from the pop-up menu (highlighted in red in the screenshot below). If necessary, click the arrow to the left of Open With to expand that section.
Click Change All to make Preview the default viewer for all files of that type.
But that’s all Mac 101. Let’s look at Preview’s more interesting import options.
Import from the Clipboard -- Since Preview is primarily seen as an image viewer, you’ve probably never looked closely at the File menu. Do that and you’ll notice that Preview doesn’t have a plain New command, but instead one titled New from Clipboard. That command does just what its name implies: it creates a new Untitled document containing the contents of the clipboard. It’s also often dimmed, because it can work only when the clipboard contains image or PDF data.
To test this, copy an image from anywhere on the Mac (try Control-clicking an image on a Web page in Safari and choosing Copy Image). Then switch to Preview and choose File > New from Clipboard. You’ll get an Untitled document containing the image.
It’s less common to copy a PDF, but if you open a PDF in Preview, select a thumbnail in the sidebar, and press Command-C, you’ll get that page in the clipboard, and choosing File > New from Clipboard will create a new Untitled PDF document with that page.
Here’s another neat trick: if you select a file in the Finder, choose Edit > Copy (or press Command-C), and then invoke Preview’s New from Clipboard command, it creates a new document containing all sizes and resolutions of that file’s icon. It’s a great way to snag an application or document icon!
Using Preview’s New from Clipboard command is far from the only way to create a new document containing an image or PDF page, but it’s handy on occasion.
Import from Cameras -- Here’s something you probably didn’t know: Preview can import images directly from cameras and scanners. Better yet, in Preview’s eyes, your iPhone or iPad counts as a camera.
To import pictures from a camera, connect it to your Mac via a USB cable, open Preview, and choose Import from CameraName (for instance, Import from iPhone).
A window appears displaying thumbnails of the photos on that camera, largely mirroring the look and features of Apple’s Image Capture utility (which lives in the Utilities folder inside your Applications folder). By default, Preview displays the photos in a list, with EXIF information like the date and time the picture was taken, file size, resolution, GPS coordinates, aperture size, whether the flash was fired, and more. Even if you don’t want to use Preview to import your photos, it’s a handy way to view all that data.
In the lower left, there are buttons to rotate photos, view photos as a list, or view photos as a grid. To rotate a photo, select it and click the curvy arrow. You can also adjust thumbnail size with the slider in the lower right.
When you want to import the photos, you have two options in the lower right. You can click Import All to get everything or select a few photos and click Import. Decide where to save the images and click Choose Destination to put the pictures there.
Import from Scanners -- If you have a compatible scanner attached to your Mac, you can use Preview to import images and documents from it. Perhaps not surprisingly, the interface is also nearly identical to Image Capture’s. It’s also similar to the window that appears when you click Open Scanner from the Printers & Scanners pane of System Preferences. If your scanner doesn’t appear, you may need to set it up first from within the Printers & Scanners preference pane. Once there, you can also set Preview to open automatically when you press the Scan button on your scanner, assuming it has one.
With the scanner attached and turned on, choose File > Import from ScannerName in Preview. If the details pane isn’t showing already, click Show Details to display a wide variety of controls for resolution, size, rotation, format, and image correction. You’ll probably want to choose a resolution higher than 50 dpi (300 dpi is safe if you’re planning to print the scanned document; you might want to go higher for photos).
Pay special attention to the Auto Selection pop-up menu, which has three settings: Off, Detect Separate Items, and Detect Enclosing Box. Preview defaults to Detect Separate Items, which is appropriate for scanning multiple photos at once but isn’t right for scanning a single sheet of paper. For full-page scanning, choose Detect Enclosing Box, which tries to detect the edges of the paper and lets you adjust the scanned area by dragging the selection rectangle’s handles. If neither does quite what you want, you can select the portion of the document to scan manually by dragging out a rectangle, moving it around, and resizing it with its handles. For an easier approach when scanning full pages, choose Edit > Select All (Command-A), and then resize the selection.
When everything is set to your liking, click Scan. Preview scans the document and opens it in a new Untitled window. If it doesn’t meet your needs — this is where you realize that you forgot to reset the resolution menu from 50 dpi to 300 dpi — close it without saving. Otherwise, save and name the document to keep it. If you put multiple items in the scanner, Preview scans them to separate files, all of which are shown in a single Preview window.
One last thing. While viewing a PDF, you can add additional pages to it by choosing Edit > Insert > Page from Scanner. The scanning interface here is simpler, with only a checkbox to use the scanner’s document feeder, if available; a Rescan button for trying again; and an Add To Document button. It’s not clear how Preview chooses resolution in this scenario, but it seems to be relatively high. The page is inserted after the currently selected page, though you can also drag it around within Preview’s thumbnail sidebar.
Take Screenshots -- Those who write about technology have memorized Apple’s keyboard shortcuts to take Mac screenshots. Normal people who need to take a screenshot only a few times a year should turn to Preview instead. Just as the previous features also appeared in Apple’s Image Capture utility, the screenshot capabilities are mirrored in Apple’s Grab utility (also stored in the Utilities folder).
In Preview, choose File > Take Screenshot. There you find three options:
From Selection: After choosing this command, your cursor becomes a crosshair. Click and drag the crosshair over the screen area you wish to capture.
From Window: Choose this command, and your cursor becomes a camera. Move the camera cursor over a window and the window turns blue to indicate that it’s selected. Click to take a screenshot of that window. By default, your window screenshots come with a large shadow; to remove it, Option-click the selected window.
From Entire Screen: When you choose this command, a 10-second countdown begins, which you can cancel by pressing the Esc key. Once the countdown finishes, Preview takes a screenshot of your entire screen. If you have multiple screens, Preview creates screenshots for each one. The timer is useful when you need to set up the screen in such a way that wouldn’t be possible with an instantaneous screenshot. Although it won’t appear in the final screenshot regardless, you can move the countdown timer bar around to get it out of your way.
Unlike OS X’s screenshot shortcuts, which dump the screenshots on your Desktop, Preview opens each new screenshot as a PNG file in an Untitled window, where you can make any modifications you like before saving it. Simple, but effective.
Wait, modifications? Yes, that’s right, Preview is also a surprisingly full-featured graphic editor too. But that’s a topic for a future article. Preview may seem unassuming, but it’s packed with useful capabilities, and we’ll be looking at more of them in the future.
Article 2 of 6 in series
In the latest installment of The Power of Preview, we look deeply at how you view images and PDFs in Apple’s ubiquitous Mac document and image viewer.Show full article
In “The Power of Preview: Pulling Files into Preview” (25 February 2016), we offered tips for bringing documents and images into Preview, the surprisingly powerful document and image viewing app built into OS X. For this installment, we’re going to focus on Preview’s prime directive: viewing images and documents (primarily PDFs, although as you’ll remember, Preview can also open iWork and Microsoft Office documents).
Use and Customize the Toolbar -- In the following sections, we’ll cover a number of features available from Preview’s menus, but many of them are more easily accessed via the app’s toolbar. Regardless of whether you’re viewing an image or a document, you should see it at the top of the Preview window. If it’s not showing, reveal it by choosing View > Show Toolbar or pressing Command-| (that’s not an uppercase “I” but instead a pipe character, which is accessed by typing Shift-Backslash, using the key above Return). There’s also a separate Markup Toolbar, which we’ll cover in a later article.
Like a good Mac app, Preview lets you customize which controls appear on the toolbar. Plenty of controls are available, all of which duplicate menu commands. To get started, choose View > Customize Toolbar. Here are the buttons you can add to the default set:
- A Zoom button set that includes an Actual Size button
- Zoom to Fit and Actual Size, as described below
- Scale, which enables you to zoom to a specified percentage
- Previous and Next page buttons for page-by-page PDF navigation
- Back and Forward page history buttons for link-based PDF navigation
- Page, which lets you jump to a specified page
- Slideshow, which starts a slideshow — more on that shortly
- Inspector, for showing and hiding the Inspector window
- Magnify, which displays a loupe for examining small details or text
- Selection, for switching to rectangular selection mode quickly
- Print, for opening the Print dialog
Thumbnails and Table of Contents in the Sidebar -- When it comes to navigating among multiple images and PDF pages, Preview’s sidebar is your friend. Preview tries to be smart about displaying its sidebar, so if you open multiple images, the sidebar automatically appears. Preview isn’t smart enough to show the sidebar automatically for multiple-page PDFs and to hide it for single-page documents, but it does try to remember your previous selection, either in general, or for a particular document, and restore that state of the sidebar. It’s usually best to display the sidebar for multiple-page documents.
You can hide the sidebar by choosing View > Hide Sidebar. That command is a one-way toggle; if Preview’s sidebar is showing, choosing Hide Sidebar makes it disappear and puts a checkmark next to the menu command. Choosing it again does nothing; to reveal the sidebar, you must instead choose another of the sidebar-related commands. If the sidebar is showing, you can also hide it and reveal it again by shrinking and expanding the window horizontally.
For viewing multi-page documents and collections of images in the sidebar, you have two main options: View > Thumbnails (Command-Option-2) and View > Table of Contents (Command-Option-3). The former shows graphical previews of images and document pages, while the latter displays a text list of image file names or PDF bookmarks. Regardless, clicking an item in the sidebar navigates to the associated page. Remember that you can drag the sidebar’s divider to the right to see the images or pages larger, or see more of the sidebar text; dragging it left makes more room for the current image or page.
When you’re showing the table of contents in the sidebar, you can navigate through its entries with the keyboard: the Up and Down arrow keys do what you’d expect, but the Right arrow key expands a hierarchical ToC level, and the Left arrow key collapses the outline again.
You can also view images and pages as thumbnails in a single-window grid with View > Contact Sheet. Double-click any thumbnail to focus on it. We’ll talk more about these features in a future article, but notice that you can drag pages around in a PDF to rearrange them, or even select one or more pages and press Delete to remove them (the same is true of Thumbnail view).
Here’s a tip we should have mentioned in our previous article about opening files. Let’s say you have a group of images open in a window, and you want to open more images in that same window. You can drag them from the Finder into the Thumbnail view of the sidebar, or into the Contact Sheet view, to do just that.
And, let’s say you’re evaluating a bunch of images and you need to delete some. You can do that right from within Preview; with the unwanted image selected, choose Edit > Move Selected Item to Trash or just press Command-Delete. It’s great for winnowing out bad images.
Highlights, Notes, and Bookmarks in the Sidebar -- The next option in the View menu is Highlights and Notes (Command-Option-4), and it requires a bit more explanation. As you read a PDF, you can highlight passages and add notes, and later access them via the sidebar.
To highlight text, first choose Tools > Annotate > Highlight Text or, for an easier approach, use the Highlight button in the toolbar. Click it, and it turns blue, with the yellow highlighter enabled by default. Click the arrow next to the button to choose among several highlighter colors, as well as underline and strikethrough.
While Highlight is enabled, select text in the PDF to highlight it. Control-click the highlight to add a note, change the highlight style, or remove the highlight entirely.
If you choose Add Note, a box appears, into which you can enter text. When you’re done, click outside that box, and it shrinks down to a smaller box attached to the highlight. Click the little box to expand the note. These features combine to provide a great way to take notes on a PDF while you’re reading and refer to them later.
You can also bookmark pages in a PDF, by either choosing Tools > Add Bookmark or pressing Command-D. A little red bookmark appears in the upper-right corner of the page to indicate that the page has been bookmarked.
To view your bookmarks in the sidebar, choose View > Bookmarks (Command-Option-5). To delete an unneeded bookmark, select it in the sidebar and press Delete.
It’s worth noting that Adobe Acrobat Pro and Adobe Reader use the term “bookmark” for items in what Preview calls the “table of contents.” What Preview calls “bookmarks” are, as far as we can tell, specific to Preview, so don’t assume that anyone reading your PDF in one of Adobe’s programs can see them.
Zooming In and Out -- Under the View menu, there are options to Zoom In and Zoom Out. Those commands are self-explanatory, but note that they also work in Contact Sheet view. Don’t rely on the menu commands, though, since there are more efficient ways to zoom in and out. Command-= (remember it as Command-plus, but you don’t need the Shift key) and Command-- (Command-minus) zoom in and out, respectively, as does pinching in and out on a trackpad.
The View menu offers additional choices for document zooming: Zoom to Fit (Command-9), which fills the window with the document or image, and Actual Size (Command-0), which does just what it says, regardless of whether the file fits in the window or not. Zoom to Fit in a large window is usually the best way to read PDFs.
For even more control, you can make a marquee selection in an image or PDF (choose Tools > Rectangular Selection and drag out a rectangle) and then choose View > Zoom to Selection.
A useful accessibility tool for those without perfect vision is the Magnifier, under Tools > Show Magnifier (though it’s easier to engage it by pressing the Backtick key, just above the Tab key). It turns your cursor into a magnifying glass inside Preview, providing a loupe to expand a portion of an image or making small text in a PDF easier to read. Turn it off quickly by pressing Esc.
PDF Navigation -- Although it may not have exactly the same capabilities as Adobe Reader, Preview is a robust PDF reader. Along with the previously mentioned options for navigation within a PDF, the View menu offers three options for how you view PDFs: Continuous Scroll, Single Page, and Two Pages. View > Continuous Scroll (Command-1) lets you see the bottom of one page and the top of the next one as you scroll through. Choose View > Single Page (Command-2) to scroll through a document page by page, and View > Two Pages (Command-3) to scroll through by two-page spreads. Which is best for you depends on personal preferences, the document in question, and your screen size. Happily, you can set your favorite in Preview’s preferences; more on that in a moment.
The easiest way to scroll through a PDF is with a trackpad or mouse, but you can also use the arrow keys, Page Up and Page Down, and Home and End. If you look in the Go menu, you see commands for Up, Down, Previous Item, and Next Item, but this is a case where the keyboard shortcuts are infinitely preferable — the Up and Down arrow keys move in those directions, and Option-Up arrow (or Page Up) and Option-Down arrow (or Page Down) activate Previous Item and Next item.
The difference between Up/Down and Previous/Next Item depends on context. For instance, if you have the document pane selected and a PDF zoomed so less than a full page appears, Up and Down scroll a few lines at a time, but Previous/Next Item scrolls a page at a time. However, if you have the Table of Contents sidebar selected, Up/Down moves between ToC entries, while Previous/Next Item moves between pages.
That may seem a little confusing, but as a rule of thumb, if the arrow keys don’t do what you expect, hold down the Option key while pressing them (which is also true for many commands in OS X). Or just use Page Up and Page Down whenever you want to navigate by pages.
Good PDFs like our Take Control books feature links to other parts of the document. That’s where the Back and Forward commands in the Go menu come in handy. Choose Go > Back (Command-[) to bounce back to the link you clicked. Then, Go > Forward (Command-]) returns you to that link’s destination.
You can also jump to a specific page by choosing Go > Go to Page (Command-Option-G). In the dialog that appears, enter the page number, and press Return or click OK. If you don’t end up at the page you expect, see the explanation of Use Logical Page Numbers below.
Full Screen and Slideshows -- Sometimes you want to cut out distractions while reading a PDF. Or perhaps you want to display a collection of images or a PDF-based presentation (like those we create for some of our Take Control books) for a group. Preview offers two useful options for that under the View menu: Enter Full Screen and Slideshow.
Choosing View > Enter Full Screen (Command-Control-F; you can also just click the green zoom button) puts the window into OS X’s standard full-screen mode. If you’re viewing a PDF, you can choose among the usual Continuous Scrolling, Single Page, and Two Pages views. Continuous Scrolling is the odd one here, since it also zooms the document to fit the width of your screen. Within full-screen mode, you can use the same trackpad, mouse, and keyboard navigation controls.
Choosing View > Slideshow (Command-Shift-F) displays the current document or image fullscreen, and advances the slide every 5 seconds. (For images, you need to open all the images at once, so they appear in the same window — more on that in a moment.) A toolbar displays near the bottom of the screen, with controls to move between slides, play or pause the slideshow, and exit the slideshow. You can use the toolbar buttons or the arrow keys to move between slides manually; pressing Esc exits.
Search -- Assuming that Preview sees a document as containing text (which is not true of all PDFs), you can enter a search term in the toolbar’s Search field to find all instances in the document. If the toolbar isn’t visible, choose Edit > Find > Find (Command-F) to get a Search dialog.
Regardless, Preview highlights any found words, search results show in the sidebar, and a search toolbar provides buttons that enable you to sort the results by search rank or page order. We find Preview’s search rank entirely inscrutable; stick with page order. In that search toolbar, Preview also provides arrow buttons for cycling through the results and a Done button that leaves search mode (you can also click the X button next to the search term).
Frustratingly, Preview searches for multiple words independently by default, which usually provides too many results. To search for a phrase, surround the words with double quotation marks.
Although searching may not seem useful when viewing images, if you’ve opened a bunch at once, you can search for text in their file names to limit the sidebar list to just those that match.
Setting Preview Preferences -- Although the number of options for how Preview displays images and PDFs may seem overwhelming, most people prefer the same views most of the time, and you can set your favorites in Preview > Preferences.
General: There are two settings here. The first affects how Preview opens files. You can choose to open all files in one window, open groups of files in the same window, or open each file in its own window.
The first option for how files should open is often confusing. Let’s say you have a Take Control PDF book open in Preview, and you double-click a JPEG-based photo in the Finder. It will open in the same window as the book!
If you select the third option, when you select multiple images and open them in Preview, they all open in separate windows, which is overwhelming and makes navigation far more difficult.
The default option, Open Groups of Files in the Same Window, is generally the best choice.
The second setting in the General pane is for the window background, letting you customize the color of the empty space around documents and images. The default is gray, but you can use the color picker to make it any color you wish.
Images: There’s only one setting here: Define 100% Scale As. There are two options: 1 Image Pixel Equals 1 Screen Pixel and Size on Screen Equals Size on Printout .
This affects how files are displayed when you choose View > Actual Size. We’ll be honest here — we have no idea why you’d choose one option over the other, so we recommend keeping it at the default, which is 1 Image Pixel Equals 1 Screen Pixel.
PDF: Things here are a bit more interesting. The first setting is again Define 100% Scale As, and again, we suggest leaving it at the default option of 1 Point Equals 1 Screen Pixel.
The next setting is a checkbox that tells Preview to open documents on the last-viewed page, which is checked by default and makes it easy to return to your place when reading a PDF-based book. If you do a lot of PDF creation and testing, deselect it so PDFs always open to the first page.
Next is Opening for the First Time, which sets how to display pages. The options here are Continuous Scroll, Single Page, and Two Pages, as described above. Choose the one that best fits your working style. Continuous Scroll is probably best on smaller screens; Single Page or Two Pages may be better if you have a 27-inch screen.
The next setting is to Smooth Text and Line Art, which is enabled by default. Unless you find that text looks blurry in Preview, keep this on.
After that is Use Logical Page Numbers. This setting tries to help with documents that have early pages denoted with Roman numerals instead of Arabic numbers, as explained in this Apple support article. Usually, it’s best to keep it enabled, but if you have trouble hitting the correct page when using Go to Page, turn it off.
The last setting is Add Name to Annotations, which marks highlights and notes with your name. This is useful if you’re collaborating on a PDF with other people, so you can see who marked up what. You can enter your name here, but it will probably already be filled in for you, from your user account profile.
View Metadata with the Inspector -- That’s about it for what you can do in Preview with viewing images and PDFs, but what about the metadata surrounding those files? That’s where the Inspector comes in handy. Choose Tools > Show Inspector (Command-I) to reveal the Inspector window.
Whether you’re viewing a document or an image, the first pane in the Inspector is General Info, which shows things like file size, resolution, creator information, and when the file was created.
The other panes vary depending on whether you’ve viewing an image or a PDF:
More Info (images only): This pane shows advanced image information, like EXIF data, color data, resolution, and DPI.
Keywords: Here you can add keywords to a document or image so that those files can be found more easily in Spotlight. Click the plus button to add keywords and click the minus button to remove them.
Encryption (PDFs only): This pane tells you if the PDF is encrypted, and if so, what permissions you have. Yes, Preview can encrypt your PDFs, and we’ll cover that in another article.
Crop (PDFs only): This pane shows you the dimensions of the area selected with the Rectangular Selection tool. You can crop a PDF page to those dimensions, something we’ll cover in another article.
Annotations: Use this pane to view and jump to your highlights and notes — just like the sidebar. You can also add new notes to a highlight by selecting it and typing in the lower portion of the pane. For an image, anything you add counts as an annotation.
This is the second article in our series on the power of Preview, but we’re still just scratching the surface of what Preview can do. If it could do only what we’ve outlined in these first two articles, it would still be an entirely worthwhile app. But there’s so much more in Preview to show you!
Article 3 of 6 in series
In the latest installment of our exploration of Preview, OS X’s built-in document and image viewer, we delve into Preview’s editing capabilities, explaining how to crop and resize files, plus how to recover from unwanted changes.Show full article
In “The Power of Preview: Pulling Files into Preview” (25 February 2016) and “The Power of Preview: Viewing Images and PDFs” (13 March 2016), we walked you through the basics of opening and viewing files in Preview, OS X’s venerable, all-purpose document and image viewer. This time, we begin digging into Preview’s image manipulation capabilities.
As writers of technical articles and books, we work with screenshots constantly, and Preview saves us time over using more full-featured tools like Pixelmator or Photoshop, thanks to Preview’s focused tool set. You can even take screenshots from within Preview itself, as noted in “The Power of Preview: Pulling Files into Preview”.
The most common tasks we perform when editing screenshots are cropping and resizing, to cut out unneeded elements and keep images from being too large. Preview excels at both of these tasks.
Cropping Images with Preview -- To crop an image means to remove everything outside of a selected area, and Preview makes that easy. But first, you have to understand how to use its Rectangular Selection tool.
The Rectangular Selection tool should be the default when viewing images, but if you need to activate it, choose Tools > Rectangular Selection. It’s also available on the far left of the Markup Toolbar, which you can display by choosing View > Show Markup Toolbar (Command-Shift-A).
Using the Rectangular Selection tool is simple: just click and drag to create a selection box. You can move the selection box by positioning your cursor inside the box so it becomes a hand — after that, click and drag to move the box. Likewise, you can click and drag the blue circles to adjust the size of the box. As you adjust the size of the box, its pixel dimensions are displayed in a small popover, a handy aid.
In the example screenshot, we want to crop out everything but the Finder and Preview windows. Once the selection box is over the windows, select Tools > Crop (Command-K) to cut out everything that’s not wanted.
That’s not hard, but here’s a technique that simplifies creating precise crops around windows, dialogs, and other objects.
First, don’t attempt to make a precise selection, since that can be tricky. Instead, drag out a rough selection around the desired object that includes some of the background, and then press Command-K to make an initial crop.
Then use the blue handles in the middle of each side of the selection rectangle to move each side in to exactly the desired position before cropping again. That requires four actions, but can be more precise than using the corner handles, which resize the selection in two dimensions at once. It can be hard to get both sides exactly right at the same time.
If you’re cropping a very small object, such as the buttons we use as inline graphics in Take Control books, after making that initial rough crop, zoom in closely so you can see the object’s exact edges before dragging the side handles in to make your final selection and then cropping. For zooming instructions, refer back to “The Power of Preview: Viewing Images and PDFs.”
Here’s a final tip to remind you of a feature we mentioned in “The Power of Preview: Pulling Files into Preview.” If you make a rectangular selection, instead of cropping, you can copy the selection and then choose File > New from Clipboard to create a new document containing the copied data. In other words, a selection followed by Command-C and Command-N is a quick way to get a new file containing your desired content — it’s another path to a cropped image that might be more appropriate in certain workflows.
We’ve focused on images here, but you can also crop PDFs using the same method. This is rarely useful, and note that Preview crops only a single page at a time. Plus, since Preview doesn’t actually delete content, but instead just hides it, the PDF will likely appear uncropped in other apps. Preview even warns you of this fact.
Resizing Images with Preview -- You’ve cropped out the parts of the image you don’t need, but it’s still too large, either in terms of dimensions or file size? Again, Preview makes it easy to shrink the image.
Choose Tools > Adjust Size and a handy dialog appears. Play with the settings and either click OK to apply your changes or Cancel to back out. Here’s a quick overview of what each of the controls does:
Fit Into: This dropdown menu gives you a set of predefined sizes to fit the image into. These sizes match common screen sizes, and are most useful for making wallpaper images. If your image doesn’t match the aspect ratio of the pre-defined size you choose, Preview fits the longest side of your image to the appropriate dimension. So a portrait image will always be fit to the height of the pre-defined size, and landscape images will be fit to the width. When you adjust the width and height yourself, this menu sets itself to Custom; you don’t need to choose that manually.
Width and Height: In these fields, you can manually set the width and height of the image. The pop-up menu on the right lets you set the unit of measurement: pixels, percent, inches, centimeters, millimeters, or points. Which of these you choose depends mostly on how you think about your output.
If you’re planning to use the image on a Web site, pixels likely makes the most sense, whereas if it’s destined for a printed document, a real-world measurement like inches, centimeters, or millimeters may be more helpful. If the actual size doesn’t matter too much, you can shrink it by a percentage.
One tip that applies to all image editing: you can always scale images down, but you don’t want to scale images up. Unlike what you may see on TV shows, scaling an image up almost never works well, because Preview has to generate pixels out of thin air, and the resulting image is always blurry.
Resolution: Here you can adjust the resolution of the image, in either pixels per inch or pixels per centimeter. Resolution is a tricky topic, but in short, for images destined for the screen, it’s usually irrelevant and can be ignored. For screen display, all you care about is how many pixels the image has — whether it’s 72 ppi or 144 ppi should make no difference in how it looks onscreen. Don’t assume that reducing the resolution will make the file size smaller either; it will if you select Resample Image because you’re throwing away pixels, but if you don’t resample the image, the file size will stay roughly the same and may even increase somewhat for JPEGs.
For images you want to print, resolution is important to know. If you have a 72 ppi image, it will need a lot more pixels to print at a decent size on paper than if it’s a 300 ppi image. But you can’t change the resolution to get better results because any change in resolution must either throw pixels away or add pixels in, neither of which is good for the image. In short, unless you know what you’re doing, leave the resolution setting alone. For a good discussion of resolution, see the Photoshop Essentials site’s explanation.
Scale Proportionally: In nearly all cases, leave Scale Proportionally selected, because otherwise your image will be stretched or squished in the dimensions that change.
Resample Image: As noted above, resampling changes the number of pixels in the image. Thus, it should be selected in most situations, particularly when the image is destined to be displayed on a screen, where you want to control the pixel dimensions. And in fact, if you deselect Resample Image, you can no longer choose pixels in the pop-up menu next to Width and Height, Scale Proportionally is locked on (since disproportionate scaling would change the number of pixels), and any changes you make in Width and Height also change Resolution. All you can do then is change how large the image will print. Again, Photoshop Essentials has a nice explanation.
Resulting Size: This feedback area is useful to watch, particularly if you’re trying to reduce the file size of your image. As you adjust the image’s pixel dimensions, it tells you the resulting percentage size of the original image, the resulting file size, and the previous file size. Changing resolution while resampling doesn’t affect size much, and Preview doesn’t report on such changes.
It’s extremely easy to get confused when playing with image size settings because Preview honors the physical dimensions (which are based in part on resolution) when displaying images and attempts to open all images at actual size. In our discussion of Preview’s preferences in “The Power of Preview: Viewing Images and PDFs,” we said that we had no idea why you’d choose between 1 Image Pixel Equals 1 Screen Pixel and Size on Screen Equals Size on Printout for Define 100% Scale As. Now we understand. When you see “100%,” think “Actual Size.”
If you’re working with images primarily for display on screen, such as on Web pages, it’s probably most sensible to choose 1 Image Pixel Equals 1 Screen Pixel. That way, if you open a 1920-by-1280 image that’s 300 ppi, Preview displays it at its actual size in pixels. A 1920-by-1280 image that’s only 72 ppi opens at exactly the same size. That’s what you’d expect, since resolution isn’t relevant to publishing on screen.
However, if most of your image work is destined for print, selecting Screen Equals Size on Printout may be helpful, since then, assuming the same pixel dimensions, a higher-resolution image appears smaller and a lower-resolution image appears larger, just as would happen on a printout. In that case, Preview displays the 300 ppi image at a much smaller size than the 72 ppi image when both are at actual size.
The problem with Preview honoring the resolution-dependent physical dimensions is that other graphics programs, like Graphic Converter, focus only on pixel dimensions. If you work in other graphics apps too, Preview may confuse you by displaying the same image differently. So don’t get too wrapped up in how something looks in Preview; just focus on the pixel dimensions for screen-destined images.
Undoing It All -- The safest approach when editing an image is to make a copy before modifying it, but it’s easy to forget to do that. In that case, you have two ways to undo unwanted changes.
The first is the hoary Edit > Undo (Command-Z) command, which lets you undo recent actions. There’s also Edit > Redo (Command-Shift-Z), which lets you redo actions that you’ve undone. Nothing new there.
But if you’ve already saved and closed a file, and later reopened it, you can’t use the Undo command. Thankfully, you can still revert to an older version, thanks to Preview’s support for the Modern Document Model (see “The Very Model of a Modern Mountain Lion Document,” 7 August 2012). Choose File > Revert To, where you see two options: Last Opened and Browse All Versions. Last Opened reverts all changes made to the file since you last opened it.
Browse All Versions displays a Time Machine-like interface, with the current version of the document on the left and previous versions on the right. Use the arrow buttons to move between versions — unfortunately, it’s usually impossible to discern the differences between versions that have just been resized, so you may have to guess based on the timestamp. Click Restore to restore the file to the version showing on the right, or click Done to cancel.
We’ve barely touched the modifications you can make to documents and images in Preview, but this article lays the groundwork for future exploration. You now understand how to select parts of a file and undo unwanted changes. Next, we’ll dig deeper into Preview’s image-editing power.
Article 4 of 6 in series
We once again explore the power of Preview, OS X’s built-in document and image viewer, with a focus on using Preview to annotate images and PDFs.Show full article
The last time we explored Preview, OS X’s built-in document and image viewer, we discussed using it to crop and resize images, as well as how to undo those changes (see “The Power of Preview: Cropping and Resizing Images,” 18 March 2016). Although Preview has many more image manipulation tools, we’re focusing this week on Preview’s annotation capabilities, which you can use to mark up an image or PDF (you can’t annotate Microsoft Office or iWork documents).
Most of Preview’s annotation tools are available in the Tools > Annotate menu, but it’s often easier to find them in the Markup Toolbar, which you can display by clicking the toolbox icon on the main toolbar, or by choosing View > Show Markup Toolbar (Command-Shift-A).
The Colour and the Shape -- The Preview annotation tool we use most often is Shapes, which makes it easy, for instance, to call out a particular interface element in a screenshot. You can find all available shapes under Tools > Annotate > Rectangle, Oval, Line, Arrow, Polygon, and Star. However, it’s usually faster to access Shapes on the Markup Toolbar.
Whether using the menu or toolbar, choose a shape to insert it into your document or image. It appears in the center of your document; to insert a new shape at a particular spot, click Shapes on the Markup Toolbar, and then drag the desired shape to the spot you want.
A selected shape is surrounded by blue drag handles you can use to adjust the shape’s dimensions. As in many image manipulation apps, you can press Option while dragging a handle to resize from the center, and press Shift to maintain the shape’s aspect ratio. For lines and arrows, the Shift key constrains the line to 45-degree angles.
You can, of course, move the shape, by placing your cursor on the shape anywhere other than on a drag handle — when your cursor becomes a hand, click and drag to move the shape. Or just click once to select the shape, after which you can use the arrow keys to nudge it more precisely.
As is often the case, if you need more than one shape of the same type, you can either use copy and paste, or simply hold down Option and drag the shape, as if to move it, to create an exact duplicate.
The line, polygon, and star offer additional possibilities. When first inserted, lines are straight, but a green drag handle in the middle of the line lets you make it into a smoothly curved line. By default, inserting a polygon adds a hexagon to your document. But if you select it and look closely, you’ll see another green drag handle. Move that handle counter-clockwise to remove sides, down to three, or clockwise to add sides, up to 12. The star shape works similarly, except it has two green handles, one that adds or remove points and another you can use to change the length of the points. For both the polygon and the star, the Shift key’s behavior is reversed; the resizing handles maintain aspect ratio by default, and the Shift key lets you change the horizontal and vertical dimensions independently.
It’s possible to rotate a shape, too, but only if you have a trackpad. Select the shape, put your thumb and forefinger on the trackpad, and twist. Make sure you have a shape selected first, because otherwise Preview rotates the entire image (in 90-degree increments).
After adjusting the shape, size, and position, you can further customize the shape’s look with options on the Markup Toolbar:
Shape Style: Use this menu to adjust the thickness of the shape’s exterior line, generally called the “stroke.” You can also make the stroke dashed or rough-drawn, as well as add or remove a drop shadow. For line and arrow shapes, you can also choose where to place arrows.
Border Color: Click this button to display a color picker that lets you adjust the color of the shape’s stroke.
Fill Color: Similarly, this button reveals a color picker that lets you adjust the color of the “fill” — the space inside the stroke. By default, it’s set to “no fill,” signified by a red line across a white square.
There are a few ways to use these tools in constructive ways other than inserting pretty shapes. A technique we use frequently at TidBITS and Take Control is to place a red oval or rectangle with no fill around interface elements we want to draw attention to. Even if you’re not a technology writer, snapping a quick screenshot (which you can do from within Preview, as you learned in “The Power of Preview: Pulling Files into Preview,” 25 February 2016), highlighting an onscreen item, and sending the annotated screenshot to a friend can save time and frustration when trying to assist with a technical issue. Arrows can also be useful for pointing out specific details.
Shapes can also be helpful for redacting text from PDFs that you’re planning to print. Create a rectangle with a black stroke and a black fill and drag it over a portion of a document you wish to obscure. When you print the document, the black rectangle will cover the sensitive material. (Josh once had a job that involved doing this for thousands of documents, albeit not with Preview.) Don’t assume this technique will work for PDFs you’re distributing digitally; the shapes remain editable objects that can be moved and deleted in both Preview and Adobe Reader. For a true redaction capability that deletes the text underneath the black bar, use Smile’s PDFpen or Adobe’s Acrobat Pro.
Preview remembers your settings, so if you generally want shapes with 3-point red strokes and no fill, you’re all set. Unfortunately, there’s no way to save different settings, so if you switch to a black rectangle, reverting to your previous settings must be done manually.
With PDFs, annotations remain unique, editable objects, even after you save, close, and re-open a document. However, with images, that’s not true. Once you close an edited image, all your annotations are flattened into the underlying bitmap of the image and can no longer be selected and manipulated individually. In other words, make certain that you’re done adjusting annotation shapes before you close the file.
One final tip here. You might think that you could use Edit > Select All (Command-A) to select all the annotations you’ve made and delete them. You’d be wrong; that selects all the previously existing picture content instead. However, you can Shift-click multiple objects to select them simultaneously for moving or deleting all at once.
Who Was That Masked Loupe? -- For an alternative way to call things out, check out the Mask and Loupe shapes, both available from View > Annotate and the Shapes button menu in the Markup Toolbar.
Mask is a bit tricky to use because it’s sort of a reverse shape: the actual shape is a large gray border that deemphasizes what it covers. Inside that border is a “no fill” rectangle that you position over the portion of the image you want to highlight. The blue drag handles work as you’d expect, but to select or move the rectangle, you must click outside it, not inside, like every other shape. Play with the mask shape on a throwaway image so you can get a sense of how you might use it.
Loupe inserts an onscreen magnifying glass, which is a helpful way to highlight small details, but it also distorts the image, which can be confusing to the viewer. You change the size of the loupe with the blue drag handle and adjust the zoom level with the green drag handle.
The Pen Is Mightier -- If you’d rather draw shapes yourself, Preview lets you do that. In the Markup Toolbar, the third button from the left activates the Sketch tool, which doesn’t appear to have a menu equivalent. Select it, and click and drag to draw the desired shape.
What Preview does next depends on what you drew. If Preview thinks you were trying to draw a square, for instance, it changes your drawing to be a proper square shape. Likewise with triangles, ovals, lines, arrows, and other shapes — it’s a loose interpretation. Usually, if you draw an unidentifiable squiggle, Preview will leave the squiggle as is, but its behavior isn’t always predictable.
Thankfully, if you don’t care for Preview’s interpretations, or if Preview couldn’t see that you meant to draw a dialog balloon, you have a chance to correct it. After drawing a shape, look closely at the upper left of the window, where a small popover appears with your original and a choice of possible replacement shapes. Click the one you want, but be aware that you get only one shot, since the popover vanishes forever after you choose, or if you deselect the shape.
If you happen to have a trackpad equipped with Force Touch, note that the Sketch tool is pressure-sensitive, so you can press more firmly to darken the line as you draw.
The Sketch tool can be useful in ways you might not expect. For instance, imagine that you’re trying to give someone directions on a trail. Bring up the area in satellite view in Google Maps, take a screenshot, and then use the Sketch tool to draw a freehand line indicating where to go.
Texting While Annotating -- Shapes are great, but what about when you want to add a description to an annotation or complete a PDF form that lacks interactive form fields? For that, you can insert text. And, not surprisingly, Preview offers quite a few ways to do so.
The main way to insert text is to choose Tools > Annotate > Text (Command-Control-T) or click the Text button in the Markup Toolbar. Preview inserts a text box, with “Text” as a placeholder. You can move and resize this text box just as you would a shape, although it can be a little fussy, since clicking inside the text box edits the text instead of grabbing the box. Try these techniques to make moving it easier. First, click anywhere else to deselect the text box, hover over the deselected text box until you see the hand cursor, and then click and, without letting up, drag. Second, if the text box is already selected, hover over the outlined edge to get the hand cursor and drag.
To change a text box’s typeface, point size, color, style, and alignment, select the text box and click the Text Style drop-down menu in the Markup Toolbar, which is the rightmost button. You can’t style individual words or characters in the text box separately.
You can also use the Shape Style, Border Color, and Fill Color menus to further customize the look of the text box, just as you can with shapes. Border Color lets you add a border to the text box and give it a color, Shape Style offers stroke thickness and style choices, and Fill Color adds a background color to the text.
For more fun, try speech bubbles, which you insert by choosing Tools > Annotate > Speech Bubble or from the Shapes button in the Markup Toolbar. They work just like regular shapes, with the addition of two green drag handles for controlling the tip and base of the arrow. They can be fun for snapshots, but we’d caution you against using them in professional documents.
In fact, although it’s not inherently obvious, you can actually add text to any of the shapes, including lines and arrows. For those two, the text appears off to one end of the line; for the rest, the text shows up inside the shape.
Take Note -- In “The Power of Preview: Viewing Images and PDFs” (13 March 2016), we discussed highlighting text in PDFs and adding notes to your highlights. That’s all fine and nice, but what if you want to leave a comment that’s not associated with text? For that, Preview lets you insert free-floating notes, which are represented by small yellow squares that only coincidentally resemble Post-it® sticky notes. (You can’t insert notes into images.)
To insert a note into a PDF, choose Tools > Annotate > Note (Command-Control-N) or click the Note button in the Markup Toolbar. Preview adds a small yellow square to the center of the current page, popping out a larger yellow rectangle into which you can type text. Enter as much text as you want; the yellow rectangle expands to hold it. Click anywhere outside the yellow rectangle to close it, leaving just the little yellow square.
There are five things you can do with the square after clicking to select it:
Click it again to open it for editing.
Move it next to the portion of the page on which you’re commenting, which is usually a good idea.
Option-drag it to make a copy; this could be helpful if you need the same comment applied to multiple spots on the page.
Use Copy and Paste to put it on another page. Cut works too, if you created the note on the wrong page.
Press Delete to remove it from the document.
Remember that you can navigate to these notes in the sidebar, by choosing View > Highlights and Notes. Plus, you can add text to the notes in the sidebar, or edit them there, which is often easier than opening and closing the editing rectangle.
Sign on the Dotted Line -- Here’s a classic problem: someone sends you a form to sign via email. You have to print it, sign it, and then scan it back into the computer so you can email it back (or, horrors, fax it). Preview solves this problem neatly with its signature feature, found in Tools > Annotate > Signature, but more easily accessible in the Markup Toolbar. It enables you to create one or more signatures, and then easily add them to images and PDFs.
There are two ways to create a digital signature: by scanning a handwritten signature with the Mac’s webcam or by writing it on the trackpad. Obviously, if all you have is a mouse, you’ll want to use the camera method.
To create a signature with a trackpad, click the Sign button in the Markup Toolbar and choose Create Signature. Click the Click Here to Begin button and write out your signature on the trackpad with your finger — if you have a capacitive stylus for an iPad (not an Apple Pencil), it will likely work better. There’s no way to erase, so if you’re unhappy with the results, click Clear and try again. When you’re satisfied, click Done to add the signature to Preview’s list.
However, using a webcam like the FaceTime camera built into most Macs is arguably the better way to make a signature. Sign your name on a blank, white piece of paper, preferably with a black marker. Choose Create Signature and click the Camera button. Inside the popover, a window appears displaying what your camera sees. Hold your paper signature up to the camera, making sure to get it close and lined up with the blue line. When Preview detects the signature, it displays the digital version in the camera window. Again, if you don’t like the results, click Clear and try again, or if you’re happy, click Done to save the signature.
Once created, your signature is easy to insert into an image or PDF. Choose Tools > Annotate > Signature or click the Sign button again. This time, you’ll see your new signature there. Choose it to insert it into the document, where you can move and resize it like any other shape. You can also adjust its color by modifying the Border Color settings, although signatures can’t use the Fill Color option.
Although we’re not suggesting illegal forgery, if you find yourself in a situation where you often need to sign things for your boss or for an incapacitated relative, getting that person’s signature into Preview can make signing electronic forms for them much easier.
Once you save the PDF, the signature is embedded into the PDF’s visual layer, so it can’t easily be copied out and reused. Of course, someone could extract it by taking a screenshot of it in the PDF, but they could also scan or photograph a paper document to get the signature, so there’s no real difference in security either way.
Note that these signatures will sync to other Macs if you have iCloud Keychain turned on in System Preferences > iCloud > Keychain, and you can use your signatures when marking up images in Apple Mail.
We’ve now shown you how to use Preview to open and import files, efficiently view images and documents, crop and resize documents and images, and annotate documents and images. But it will be another few articles before we’re done — stay tuned for more on the power of Preview!
Article 5 of 6 in series
We again dive into the power of Preview, exploring advanced editing techniques, including more selection tools, color adjustments, and PDF editing.Show full article
In “The Power of Preview: Cropping and Resizing Images” (18 March 2016) and “The Power of Preview: Annotating Documents and Images” (2 April 2016), we explored editing and annotation tasks with Preview, OS X’s built-in document and image powerhouse. This week, we’ll go deeper with some advanced editing techniques, and double back for a few tidbits we skipped in previous articles.
Advanced Selection Tools for Images -- In “The Power of Preview: Cropping and Resizing Images,” we discussed using the Rectangular Selection tool. However, when working with images, several other selection tools offer more variety and control. You find them in the Markup Toolbar, which you display by choosing View > Show Markup Toolbar (Command-Shift-A). The selection tools are accessed via the first button at the left.
Elliptical Selection is the second choice on the selection tools pop-up menu. It works just like the Rectangular Selection tool, except that it selects elliptical rather than rectangular areas. As with the Rectangular Selection tool and the shape tools, you can press Option while making the original selection to size it from the center, and pressing Shift gives you a perfect circle.
After dragging out an elliptical selection, you get the usual drag handles. The handles attached to the selection ellipse itself adjust one dimension at a time, whereas those on the corners of the rectangle that encloses the ellipse can adjust two dimensions at once.
The next selection tool is Lasso Selection, which Bill Atkinson first invented for MacPaint in 1983. The Rectangular Selection and Elliptical Selection tools fall down when you need to select an irregularly shaped object or portion of a graphic. But with the Lasso Selection tool, you can hand-draw a selection around any object. The hard part of this is that you have to do it in a single click-and-drag motion. Since the Lasso Selection has to form a closed shape, if you don’t close it yourself by ending your drawing back on the starting point, the selection closes itself with a straight line. Once you’ve finished making a selection, you can drag the selection — not the underlying image, but the dashed line selection — around with the pointer, or nudge it with the arrow keys.
The Lasso Selection tool works well when the irregularly shaped object you want is well separated from other parts of the image. But in a photograph, for instance, you’re unlikely to be so lucky. For such situations, Preview offers the Smart Lasso tool, which offers some assistance. When you drag, you see a thick red line instead of a thin white line — draw that around the object you want to select and Preview tries to construct the selection intelligently. It will take some experimentation to get the desired results. Oddly, you can’t move a Smart Lasso selection afterwards with the pointer, but you can nudge it with the arrow keys.
Once you’ve selected something with one of these tools, you have a few options:
Choose Edit > Invert Selection (Command-Shift-I) to select everything other than what you just selected. It’s handy at times!
Press Delete to remove it from the image, leaving a hole.
Use Command-C to copy the selection, so you can paste a copy into this or another image. Remember that you can also choose File > New from Clipboard to create a new file with the copied selection.
Once you have a copy, you can move and resize it to your heart’s content, although it will always be essentially rectangular in Preview’s eyes, no matter how irregular it was to start. One technique we frequently employ is obscuring part of a screenshot by copying a chunk of its background color and pasting it over the part of the image we want to cover up.
Honestly, there aren’t that many uses for the Elliptical Selection tool, and both of the lasso tools are finicky, so we use them only occasionally. Let us know if you’ve found good uses for these tools, but if you’re just trying to remove a background from an image, the Instant Alpha tool is a better choice.
Instant Alpha -- No, Instant Alpha won’t make you leader of the pack. Rather, it’s a color-based selection tool, similar to magic wand tools in other image manipulation apps. It’s best used to strip solid-colored backgrounds from images (replacing them with transparency, which doesn’t obscure the background color on a Web page, for instance).
The Instant Alpha tool is the second button in the Markup Toolbar. Click it, and then click and hold on the colored area you wish to select. The selected area turns red; you can then drag the pointer to adjust the tool’s sensitivity to include the colors you drag over. Once you’re happy with the selection, lift your finger from the mouse or trackpad to finalize your selection.
As you’d expect, you can press Delete to delete the selection. In the screenshot below, I first used Instant Alpha to select the background, which I deleted.
Then I undid that, selected the background again, inverted it with Edit > Invert Selection, and deleted the iPads and Apple Pencil, making for a neat silhouette effect.
Realistically, though, the main time we use the Instant Alpha tool is when we’re working on a button or logo for a Web site, and the original image has a white or colored background instead of a transparent background. A few quick clicks and the background is history.
Adjust Colors -- For the most part, we’ve been talking about editing images that someone created from scratch in a graphics app, rather than photographs. However, if you do find yourself needing to edit a photograph, Preview provides some surprisingly robust image adjustment tools when you choose Tools > Adjust Color (Command-Option-C). These tools are essentially identical to those that first appeared in iPhoto many years ago.
At the top of the Adjust Colors window is a histogram with three drag handles with which you can adjust the image’s white point, black point, and midtone. Click the Auto Levels button to get a suggestion of how to reset the white and black points. Then play with each of the sliders to get a feel for how they lighten or darken the image; if you don’t like how things turn out, you can reset all of your changes with the Reset All button at the bottom of the window.
The rest of the sliders are at least labeled, but we still recommend experimentation to see how each affects a given image. Remember, you can undo your adjustments at any time with Reset All. Here’s what they do:
Exposure: If a photograph is too dark or too light due to being under-exposed or over-exposed, this slider will let you fix that. It’s mostly helpful in a small way to brighten photos that were dimly lit.
Contrast: This slider lets you control the difference between the lightest and darkest areas in a photo. It’s seldom worth messing with much, though increasing contrast a little bit can make an image look crisper and more detailed.
Highlights: This slider reveals detail in the brightest points of a photograph, which can be useful for making clouds more visible, for instance.
Shadows: More generally useful than the previous one, the Shadows slider throws light on the darker parts of a photo, revealing detail that was previously hard to see. Since you’re most likely to use it on a dark photo, it will probably lighten the entire photo as well.
Saturation: Use this slider to adjust how saturated the colors are. Moving the Saturation slider all the way to the left makes the image grayscale, which can be a useful effect, while sliding it to the right makes colors practically explode off the screen. If an image seems a little dull, try increasing saturation just a bit.
Temperature: With this slider, you can make the image cooler (more blue) or warmer (more yellow). This isn’t terribly useful, but if the photo was taken in unkind fluorescent lighting, the Temperature slider might improve it a bit.
Tint: While the Temperature slider lets you make an image more blue or more yellow, the Tint slider does the same with green and red. To make it easier to use, Apple provides a dropper next to it; select it and then click a part of the image that should be a neutral gray or white. That sets the Tint slider automatically. Click the dropper in a few different spots to see how they differ; the best way to evaluate how well it has worked is to look at some skin tones.
Sepia: This slider is a one-trick pony; it reduces the saturation of the photo using sepia tones instead of grayscale. Crank it all the way up to give your image an “old-timey” feel.
Sharpness: This slider can make your image blurrier or sharper. Blurrier might be helpful with an almost abstract sunset, but mostly you’ll want to sharpen photos to bring out more detail. Don’t go too far, though, since excessive sharpness can make the image look grainy.
To give an example of what these controls can do for your photos, here’s a photo Adam took recently at Cornell University’s Dragon Day. Unfortunately, because it was an overcast day, it looks less like a celebration and more like a funeral procession. Let’s see if we can brighten things up a bit.
First, I clicked Auto Levels to establish a baseline, and then I moved exposure up a bit to brighten the image. But increasing exposure blew out some of the clouds, so I darkened the highlights to make it look more natural, while also lightening shadows a bit to add more brightness. Then I upped the saturation to make the bright colors in the photo more vibrant. Finally, I bumped up temperature, tint, saturation, and sharpness just a bit to round things out.
The end result is a brighter, clearer photo. Now there’s a celebration!
One last note about color. Preview supports color profiles, which define how different displays or printers can output color. In View > Soft Proof with Profile, you can choose a color profile with which to preview the image, and if you want to assign a particular profile, choose Tools > Assign Profile and pick a profile from the pop-up menu in the dialog that appears. These features could be useful for graphics professionals who care deeply about color reproduction, although we suspect they’re using different tools.
Rotate Photos and Pages -- Every now and then, you end up with an image which isn’t rotated the way you want. Happily, Preview makes it easy to rotate images: choose either Tools > Rotate Left (Command-L) or Tools > Rotate Right (Command-R).
Less commonly useful than the Rotate commands are the next two in the Tools menu: Flip Horizontal and Flip Vertical. They rotate the image too, but around a horizontal or vertical center line. For example, Flip Horizontal can be helpful if you need a person’s headshot to face a different direction. Flip Vertical is useful when you need to flip a photo upside-down.
Preview can also rotate PDF pages, which is only very occasionally necessary. When you rotate a PDF page, Preview rotates just the currently selected page, which probably isn’t what you want. To instead rotate all pages, display thumbnails in the sidebar by choosing View > Thumbnails, select a page in the sidebar, choose Edit > Select All (Command-A) to select all pages, and then use the rotation commands. You can of course rotate just a subset of pages, if you want.
Crop Multiple Pages in PDFs -- In “The Power of Preview: Cropping and Resizing Images,” we said, “Preview crops only a single page at a time”. It turns out that’s not entirely true.
To crop multiple PDF pages, reveal the sidebar thumbnails as explained above and then use the Rectangular Selection tool on the page to select the area to which you want to crop (in the screenshot below, we’re eliminating the white page margins). Once you’ve made your selection, click the current page in the sidebar and choose Edit > Select All (Command-A) to select all the pages. Finally, choose Tools > Crop (Command-K) to crop every page in the document to the selected dimensions.
Unfortunately, this still isn’t all that useful, because Preview only hides content instead of deleting it, and there’s no guarantee that other PDF viewers will honor the crop. It’s probably most useful if you’re trying, for instance, to make a bunch of postcards scanned as full pages into something more viewable.
Edit and Rearrange PDFs -- As you’re probably coming to realize, Preview gives you complete control over the individual pages in a PDF from the thumbnail sidebar view. Here’s what you can do:
Rearrange pages: Click and drag a thumbnail in a sidebar and move the page to where you want it in the document.
Delete pages: Select one or more thumbnails (by Shift-clicking for a contiguous selection or Command-clicking for a discontiguous selection) in the sidebar and press Delete.
Combine PDFs: You can drag thumbnails from one document’s sidebar into the sidebar of another to copy pages between documents. Likewise, you can select all the thumbnails in a document’s sidebar and drag them into another document to combine the two. This is particularly handy for combining scanned single-page PDFs into a single file.
At this point, it might seem as though we’ve covered everything Preview can do, but we have more in the wings! Stay tuned to TidBITS to learn more about the power of Preview.
Article 6 of 6 in series
In this final installment of our series on Preview, OS X’s built-in image and PDF utility, we explore Preview’s export options and explain how to work around a common collaboration problem.Show full article
In our exploration of Preview, OS X’s built-in image and PDF powerhouse, we’ve walked you through getting files into Preview (see “The Power of Preview: Pulling Files into Preview,” 25 February 2016) all the way to advanced editing techniques (see “The Power of Preview: Advanced Editing Techniques,” 25 April 2016). As our series draws to a close, it’s time to end it in the natural place: saving and exporting your files.
Since Preview uses the Modern Document Model (see “The Very Model of a Modern Mountain Lion Document,” 7 August 2012), it saves existing files automatically as you edit. Likewise, Preview supports Resume, so if you quit Preview without saving, or Preview closes due to a crash or power outage, you won’t lose your work.
But that’s all Mac 101. More interesting is how Preview can convert your files into different formats. You can even export a PDF as an image or vice versa! That can be handy if, for instance, you have a one-page PDF flyer that you want to convert to a PNG or JPEG so it can be posted more easily on Facebook.
Three commands in Preview’s File menu help you export your files:
Export: This command enables you to save a copy of your file with a different name, in a different location, and even in a different format.
Export as PDF: As you’d expect, this command is mostly a faster way to get a PDF out of Preview. Oddly, the Export as PDF dialog lacks the Quartz filter and encryption options that the regular Export command does, and all the other options available with the next command.
Print: You may not realize this, but in OS X, you can “print” anything to a PDF! More on this in a bit, but for now, just know that using the Print dialog to export a PDF offers some advantages.
There’s also a fourth option, Save As, which doesn’t appear by default. Hold down the Option key to change the Duplicate command to Save As. But with one minor exception that we’ll cover later, Save As does the same thing as Export, so there’s no need to bother, unless you’re just working out of habit. If you prefer Save As to Duplicate, check out “Put Save As Back on the File Menu” (30 November 2015).
Converting Image Formats -- We assume that you understand the basics of naming, saving, and tagging files, so we’ll focus on the interesting bit: format selection. The Export dialog’s Format pop-up menu shows only 6 file formats by default, but if you Option-click it, Preview displays 19 choices!
This conversion capability is handy, because if you have a JPEG and need a PNG, all you have to do is open the JPEG in Preview, choose File > Export, change the Format pop-up menu to PNG (note the resulting file size estimate), and click Save.
But if you don’t already know that you need a PNG, which format should you pick? It depends on your intended destination for the file. We’ll look at PDF next, but the four most common image formats are:
GIF: An ancient format, first introduced by CompuServe in 1987, the GIF image format has been superseded by PNG in every way but one: GIF supports a flipbook-style animation, which is a topic for another article. Don’t use GIF unless you want to create an animation, or just feel like reliving the battle over how it’s pronounced.
JPEG: JPEG is great for photographs, and any image-viewing app can open JPEG images. When exporting as JPEG, you can reduce the quality to reduce the file size, which is useful for Web publishing. However, be aware that JPEG’s compression is lossy, which means data is actually thrown away during saves and can’t be recovered. Because of this, every time you edit and save a JPEG, the picture quality will degrade a little.
Don’t confuse JPEG with the JPEG-2000 format. Despite having a similar name and coming from the same group, they’re entirely different. In theory, JPEG-2000 is better, but in reality, it doesn’t offer many benefits.
PNG: Conceived as an improved, non-patented replacement for GIF, PNG is designed for Internet image sharing, as opposed to professional-quality printing (it doesn’t support non-RGB color spaces like CMYK). PNG uses lossless compression, making it ideal for images that you need to edit repeatedly, and it excels with computer-generated images that have large, uniformly colored areas, like screenshots and logos. There are two variants of PNG that support animation — MNG and APNG — but support and usage are minimal at best, so GIF remains the choice for animations.
Because of its lossless compression, photos saved in PNG format have much larger files than those saved in JPEG format. By default, OS X creates screenshots in PNG format, though that can be changed with a
defaults writecommand if necessary. (iOS screenshots are also saved in PNG format.) Be careful using JPEG for screenshots, or you may see artifacting in areas of solid color. In the example below (click it to zoom on our Web site!), the top image in PNG format is 1.4 MB, thanks to the photo background, whereas the bottom picture, saved at 50 percent quality in JPEG format, is only 152 KB. Notice that the photographic portion is nearly indistinguishable between the two, whereas the solid blue in the book cover shows artifacting, particularly near the white text, in the JPEG image.
When exporting a PNG from which you’ve removed the background with the Instant Alpha tool, as explained in “The Power of Preview: Advanced Editing Techniques” (25 April 2016), pay attention to the Export dialog’s Alpha checkbox. This setting enables or disables transparency, which sets a particular color as transparent, so the background color (of the Web page, say) shows through. If alpha is disabled, transparent portions of your image will be rendered as white.
It’s worth remembering that while PNG and GIF support transparency, JPEG does not. So if you convert an image in one of those two formats to JPEG, whatever color has been declared as transparent (usually white) may instead be rendered as another color. The code in the TidBITS Publishing System that makes thumbnails of graphics always creates JPEGs, which means that thumbnails of certain PNGs that contain transparency end up with black replacing the transparent portion of the image (at least until we notice and fix it).
TIFF: TIFF is another venerable format that has evolved over the years to be extremely capable and useful, though today it’s mostly used in the print world. TIFF files can be compressed, though that’s not required, and when saving one in Preview, you can choose from no compression, LZW compression, and Packbits compression. The two compression choices are lossless, like PNG’s compression, and LZW seems to result in a smaller file.
Also like PNG, TIFF supports transparency, but what sets it apart is its support for layers. In graphics programs like Photoshop and Pixelmator, layers enable you to work on the image as though you’re drawing on a transparent sheet of acetate. Objects on layers can be manipulated independently, and layers can be turned on or off to try various edits without committing to them. Unfortunately, Preview doesn’t support layers at all, so while it can open a TIFF that contains layers, it “flattens” them into a single layer. The same goes for edits made in Preview; you can add a shape to a TIFF and move it around while editing, but as soon as you close the image, the shape is merged with the image layer.
So, if you’re unsure, which format should you use? If the image is photographic, JPEG provides the best combination of quality and reduced file size. On the other hand, if it’s a computer-generated graphic with large areas of uniform color, like most screenshots, or if transparency is needed, stick with PNG. TIFF is useful primarily in the print publishing world; for instance, a publisher may require that screenshots for a book be in TIFF rather than PNG for color workflow reasons. Also, use TIFF if you will need to edit with layers in an app like Photoshop.
What about all those other image formats? For the most part, they’re old, uncommon, or both, at least in the Mac world. The two exceptions are Photoshop and QuickTime Movie, which are plenty common, but unlikely to be useful within Preview. Saving a file in Photoshop format does mean that Photoshop can open it natively, but as far as we can see, there’s no advantage over PNG in that regard. And we can’t figure out what file format you can open in Preview that you could later save using QuickTime Movie; animated GIFs seemed the most likely, but they can’t be saved as QuickTime movies. If you’d like to read up on these other formats, here’s a full list, with informative links:
- Microsoft BMP
- Microsoft Icon
- QuickTime Movie
Despite the length of that list, there are many more graphic formats out there. If you run across a file that you can’t open, or if you need to save an image in a format that Preview doesn’t support, turn to Lemke Software’s venerable GraphicConverter, which can import approximately 200 file formats and export in roughly 80 formats.
Exporting to PDF: Quartz Filters -- Entire books have been written about Portable Document Format (like “PDF Hacks,” “PDF Explained,” and “Developing with PDF,” all from O’Reilly Media). Originally created by Adobe but an open ISO standard since 2008, PDF is one of the tech world’s most useful file formats. In the simplest terms, PDF represents the text and graphics of a printed document in digital form. The most common usage of PDF is in printing and publication, with examples ranging from government forms to Take Control ebooks. But PDF is incredibly flexible — OS X’s Quartz rendering engine uses PDF internally, which is why it’s so easy to export things as PDF in OS X.
Preview’s Export dialog provides two extra options when exporting PDFs: Quartz filters and encryption. Quartz filters modify the exported PDF in various ways, either adjusting the look of the document or tweaking its format under the hood.
In the first category, you’ll find Quartz filters for Black & White, Blue Tone, Gray Tone, Lightness Decrease, Lightness Increase, and Sepia Tone. The tonal adjustments do what you’d expect, making the image black-and-white or turning all colors into shades of blue, gray, or sepia.
The two lightness filters apply to all colors as well, so their effects are relatively subtle in photos, but can make a large difference to colored text.
When it comes to fiddling with the document format, Apple provides Quartz filters for Create Generic PDFX-3 Document and Reduce File Size. PDFX-3 is a subset of PDF with printing-related requirements that facilitate a color-managed workflow. Honestly, if you need a color-managed workflow, you should be (or already are) using Adobe Acrobat Pro.
Reduce File Size is alluring, but beware if you have images other than photos in your document. When you use Reduce File Size, Preview uses lossy compression to reduce the quality of every image in the document, making non-photos notably fuzzy. Photos see a quality reduction too, but the effects are less noticeable. Happily, Reduce File Size has improved radically from earlier versions of Preview, which also deleted useful metadata like a PDF’s table of contents.
Exporting to PDF: Encryption -- Preview’s Encrypt checkbox may be more useful to you. If you’re sharing a PDF that contains confidential information, you can reduce the chances that it will be read more widely by encrypting the document, after which a password is necessary to display it.
In PDF parlance, the password created by Preview’s Encrypt checkbox is a “document open” or “user” password, as opposed to a “permissions” or “owner” password, which restricts editing and printing of the document. More on how to set a permissions password in a moment; you can’t do it from the Export dialog.
Preview offers no facility for entering the permissions password to override previously set restrictions, with one exception. If you open a PDF encrypted with a permissions password that prevents changes, and then try to use Preview’s File > Export or Export as PDF commands, you’ll be prompted for the permissions password. That is, unfortunately, false security because any change in a permissions-protected PDF causes Preview to make a copy that you can save. Plus, while Export may ask for a password, File > Save As does not. Oops.
To encrypt a PDF with a document open password, choose File > Export, select the Encrypt checkbox, enter a password, and then enter the password again to confirm it. From then on, when anyone — including you — tries to open the encrypted PDF, in any PDF-savvy app, they’ll be prompted for the password.
As far as we’re aware, as long as the document open password is relatively strong, there’s no way to brute force it. (If you use a weak password, a dictionary attack may be able to crack it.) You may run across utilities or Internet services like PDFUnlock that claim to be able to remove passwords from PDFs. They’re talking about the permissions password, not the document open password, and thus can’t do anything for you that you can’t accomplish more efficiently in Preview itself.
What if you want to remove a document open password from an encrypted PDF? As long as you know the password, it’s simple — just open the PDF, enter the password, and then use Export to save it again, without selecting the Encrypt checkbox. This technique might be useful if a document was confidential for a time, but no longer needs to be.
Printing to PDF: More Encryption -- As previously mentioned, you can “print” any document from any app to a PDF. This is a system-wide feature in OS X, thanks to Quartz’s foundations in PDF, and is tremendously useful for testing what a print job will look like before sending it to your printer or for saving a Web page as a PDF.
But why print to a PDF from Preview, which has built-in PDF export capabilities? For one thing, it offers more metadata and security options than Preview’s export feature, but it also solves a common Preview problem.
Since we began this series, several readers have written in with the same issue: you mark up a document in Preview, save it, send it to a collaborator, and they don’t see your annotations. We don’t know why this might happen — PDF is a standard, but that doesn’t mean every app implements it correctly — but printing to PDF appears to cause the annotations to show up properly in most cases.
To export a PDF in this way, choose File > Print. In the resulting dialog, click the PDF pop-up menu in the lower left and choose Save as PDF. (Further down in that menu, you may see a bunch of printing workflows that various apps install for you. They make it easy, for instance, to print a document to PDF and send it with Messages in one step.)
In the Save dialog that appears next, you’ll notice a few additional options. You can enter not just the filename, but also title, author, subject, and keyword metadata. This standard PDF metadata becomes visible in Preview’s Inspector window (choose Tools > Show Inspector or press Command-I), in other PDF apps, and even in the Finder’s Get Info dialog.
But there’s more! Click Security Options, and you can set both the document open and the permissions passwords for the PDF, and choose whether the permissions password will restrict changes, printing, or both.
Preview in the Rearview Mirror -- This article wraps up our series on Preview. We hope you’ve enjoyed it, and if you have more questions about Preview or tips to share, let us know. Who knows what additional features might lurk within Preview’s depths?
Finally, although we don’t have a schedule set yet, the response to this series has been so positive that we’re planning to start on a “Take Control of Preview” book.