How to Use Preview on the Mac: Apple’s Secret Image Editor

You may only have used it to open PDFs and look at images, but Apple's Preview app is capable of so much more, in fact, it is a useful tool for many common image editing and export tasks. Mac users with basic image editing needs who take the time to learn how to use Preview may never need to invest in another image editing application (though if they do, there’s Pixelmator). Here you will learn what the tools in Preview can do, and how to use the software for several useful image manipulation tasks:

You will learn how to:

• Resize an Image
• Crop an Image
• Create a File from the Clipboard
• Remove Background Items From an Image
• Combine Two Images
• Go Back in Time
• Select an Irregular Object
• What Is Invert Selection?
• Convert a Color Image to Black and White
• Understand Preview’s Adjust Color Tool
• Add a Speech Bubble to an Image
• Export an Image in Different File Formats
• Batch Convert Images

What Is Preview?

You’ll find Preview in your Applications folder.

It might interest you to learn the software is older than the OS inside today's Macs. Preview was part of the NeXTSTEP operating system that became the base of what we now call macOS. When part of NeXT it displayed and printed PostScript and TIFF files. Apple began weaving a range of useful editing tools inside Preview when it launched Mac OS X Leopard in 2007.

We’ll explain more about the tools you’ll find inside Preview before explaining some of the ways you can use the software to accomplish a range of commonly-required image editing tasks.

What Image Formats Does Preview Support?

Preview is compatible with a variety of image formats:

• PDF
• JPEG (And JPEG-2000)
• TIFF
• PNG
• OpenEXR

It also exports items in other image formats – just tap Option when you Export an image and choose the image type to see what those formats are.

Here is a good Macworld article that explains the differences between image formats.

What Are the Different Tools in Preview?

When you open an image or PDF in Preview you’ll see a range of icons populating the application bar.

From left to right the default set includes:

• Sidebar controls: These let you use and navigate the Sidebar, which can be useful if you are working through a multipage PDF.
• Magnification icons: Two magnifying glass icons let you zoom in and out of the image. (You can also use Command Minus or Command Plus to accomplish this.
• Share button: This lets you share the current image in various ways.
• Highlight: This drop-down menu becomes active when you open a PDF with a text entry bar. Its primary use is to insert a signature into PDF documents.
• Rotate: Tap this to rotate an image. (Hint: Hold down the option button when you use the Rotate button to rotate in the opposite direction).
• Markup Toolbar: This opens a range of tools you can use to edit and export your images, we’ll explain what each of these does below.
• Search: This lets you search through text in a PDF.

What Are the Different Markup Tools in Preview?

Preview has two different Markup toolbars, one for working with and editing PDFs, the other for images. You’ll find tools for text, shape creation, annotation, color adjustments and more.

From left to right the default set includes:

• Text Selection: When working with a PDF a text selection tool sits at the far left. This tool is not available here when working with images.
• The Selection Tool: This lets you choose to select an item using a Rectangular or an Elliptical tool. It also provides Lasso and Smart Lasso selection tools, on which more below. When working with a PDF this becomes a rectangular selection tool.
• Instant Alpha: For some image types you can use this tool to automatically select the background or other objects within an image. Just click the area you want to select and drag your cursor. The more you drag the cursor the more of the image will be highlighted in red to show you have selected it. Press delete to make this part of the image transparent or tap Command+C to copy your selection, making it available in Clipboard.
• Shape Tools: You can add rectangles, stars, and other shapes. There is also a Loupe tool which you can use to magnify an area of your image, just drag the green handle to decrease or the blue handle to increase magnification.
• Sketch: Sketch shapes with this tool. If Preview recognizes a shape you draw it will choose that instead. On Macs with a Force Touch touchpad, a second Draw tool appears. This is force sensitive and lets you draw thicker shapes in reaction to the pressure of your touch.
• Text: Tap this box to enter text, then drag the text to where you want it to be. You can edit font, size, and color using the Text Style tool to the right of this tier of the toolbar.
• Sign: This tool lets you sign documents if possible in the document you are using.
• Note or Adjust Color: When working with PDFs a tool that lets you add notes to documents appears here. If working with images the Adjust Color tool is available in this position. Adjust Color includes adjustment sliders for exposure, contrast, highlights, shadows, saturation, color temperature, tint, sepia, and sharpness.
• Line: Change line thicknesses applied using Preview’s tools here.
• Border colors: Change the color of any shape borders you might have applied using this tool.
• Change colors: Change the color of any shape content using this tool.
• Font: Here you can change fonts, size, font color, text layout, and apply bold, italic or underline.

Now you know what each of these tools is for, we should explore some of the image editing tasks you can do with Preview.

How to Resize an Image

One of the most common tasks for anyone who works with images, Preview is a capable workhorse., 

1. Open the image you want to resize in Preview.
2. In the Menu bar select Tools and Adjust Size.
3. The Adjust Size pane contains a range of custom settings, and also lets you configure your own image size in pixels, centimeters, millimeters, points, percent, and inches.
4. You select these in the drop-down menu to the right of image size.
5. In normal use, the image will scale depending on the first change you apply, but if you want to make an image wider or longer and don’t want to scale it then you should tap the padlock icon, which lets you change these dimensions manually.
6. When you have resized your image to your satisfaction, select OK.

How to Crop an Image

Remember those selection tools in the Markup menu? These let you select a specific part of your image, so you can crop the rest.

1. Just select a shape (or tap and drag the cursor across the image you wish to crop).
2. Position it appropriately so the parts of the image you like are selected.
3. Select the new Crop tool which will now be available in the Markup menu just to the right of the Fonts item.

How to Create a File from Clipboard

You can use Preview and the Clipboard to quickly create new images. This may be useful if, for example, you want to create a graphic based on an element of a larger image. To do this fast just follow these steps:

1. Open an image and select it, or open an image and select part of it.
2. In Menu > Edit, choose copy, or Command+C.
3. Now in the Preview Menu choose File > New From Clipboard.
4. A new window will open with the image you have copied. Now you can perform further edits, resize the image, or save it in different image formats.

How to Remove Background Items From an Image

You can also use Preview to perform simple image editing tasks, including removing unwanted backgrounds using the Instant Alpha tool.

1. Open the image you wish to remove the background from and select Instant Alpha.
2. Select and hold inside the area of the image you want to remove
3. Keeping your mouse depressed, move the pointer slightly. You should see a red overlay appear, keep moving until the area you want to get rid of has been selected
4. If you begin selecting image elements you want to keep, just move the pointer slowly in the opposite direction to deselect that element.
5. When you have selected the area that you wish to get rid of, tap Delete.
6. You may need to repeat this process to get rid of everything you want rid of.

How to Combine Two Images

Imagine you have a picture of a larger object that you would like to place on a new background. Preview lets you perform a simple image edit like this.

• Open both images in Preview (you can open them both in one single window if you select them both and then open them).
• Select the image you want to take the large object from, and use the Instant Alpha tool to get rid of the background you no longer need, as described above.
• Now tap Command-A (Select All), and then tap Command-C (Copy).
• Now move to the image you want to paste this object in and type Command-V (Paste).

The image will be pasted on top of the background picture you chose. Depending on the true dimensions of both images you may need to resize your pasted item. You do so by adjusting the blue size adjustment toggles that appear around the pasted item.

Go Back in Time

Preview has a fantastic tool that lets you navigate your image edits. Like going back in time, it will show you all the changes you have made to an image in a Time Machine-like carousel view. It’s also incredibly simple to use.

1. Just open your image.
2. In Menu > File you must choose Revert To and Browse All Versions.

The display brightness will reduce and you’ll see all the saved versions of your image.

How to Select an Irregular Object

Preview’s Smart Lasso is the go-to tool when you want to select an irregularly-shaped object. Just select the tool and trace carefully around the object you wish to select and Preview will do its best to select the correct portion of the image. You can use this to remove items or to copy them for use in other images.

What Is Invert Selection?

If you explore Preview’s Edit Menu you may have come across the Invert Selection command. This is what it is for:

1. Take an image and use one of the selection tools to select an area of that image.
2. Now choose Invert Selection in the Menu bar, you’ll see that the items that are now selected are all those that were not previously selected.

This is a useful tool if you have a complex object you want to select that is set against a less complex background, because you can use the Smart Lasso tool to select that background, and then use Invert Selection to accurately select the complex item. It can save you so much time in contrast to the alternative of laboriously using the Lasso tool to select the item.

Convert a Color Image to Black and White

You can easily convert an image to black and white using Preview.

1. Open the Image, and launch the Adjust Color tool.
2. Slide Saturation all the way to the left to remove all color from the image.
3. Now you can tweak the Exposure, Contrast, Highlights, Shadows, and Levels tools to see if you can improve the overall appearance of this image. 
4. If you don't like the results just select Reset All to return the image to its original state.

Get to Know Preview’s Adjust Color Tool

Adjust Color is far from being the most sophisticated color adjustment tool on any platform, but it can help you tweak an image to look much better.

It includes adjustment sliders for exposure, contrast, highlights, shadows, saturation, color temperature, tint, sepia, and sharpness. It also includes a histogram with three active sliders you can use to adjust color balance.

It’s OK to experiment – not only do you see a live preview of changes as you apply them, but if you mess the image up you can return it to its original state by tapping Reset All to return it to its original state.

The Exposure tool lets you improve photos quickly, while the Tint and Sepia tools can help you create an old-fashioned seeming image.

You can also use these tools to adjust the white point within your image. To do this, just tap the eyedropper tool eyedropper tool icon (it’s just by the word Tint) and then click a neutral gray or white area of your image. 

How to Add a Speech Bubble

You can add a speech bubble containing text to any image.

1. Select the Shapes button and choose the speech bubble shape.
2. You change the thickness of the speech bubble lines using the Line tool.
3. You alter the color of the border using the border colors tool
4. And change the fill color of the speech bubble using the colors tool.
5. Once you have the bubble created to your satisfaction, tap the text icon and a text field will appear on your image. Type the words you want to see and then move them to fit inside the speech bubble. You adjust the appearance of the font in the Fonts menu.

How to Export an Image in Different File Formats

We mentioned Preview's versatility with multiple image formats. The great thing is the application can not only open images in all these formats, but can also shift images between them, doing so is ever so easy:

1. Open the image you wish to export, perform any image editing operations you need to transact, and choose Menu > File > Export.
2. The Save dialog will appear: look for the Format item, a drop-down list that contains all the currently active formats, select the one in which you wish to save your image.

How to Batch Convert Images

You can use Preview to batch convert multiple images into a new image format.

1. Just select all the images in Finder and drag-and-drop them on the Preview icon in your Dock. A Preview window will open with all the images previewed (sic) in the left-hand sidebar.
2. Now select the sidebar and choose Select All from the Menu.
3. With all these images now selected open File > Export Selected Images. in the Menu bar. (If you only see the word ‘Export’ then you have not selected all the images.
4. Choose the desired image format in the Save dialog (as described above).