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How to resize a digital photograph using Preview software

=== by Bob Sutherland ===

A lesson on how to resize a digital photograph using Preview software by Apple for Macintosh computers.

Preview is a free program that is installed with the macOS operating system on all Macintosh computers. The primary purpose of the program, as the name suggests, is to allow people to view a wide variety of different image file types. The program has some photo editing capabilities including the ability to resize digital photos.

The following are screenshot images I captured of my computer screen as I worked through the process of resizing a digital photograph.

Preview application icon
This is what the Preview application icon looks like.

The first step is to start up the Preview application and open a file that contains a photograph. There are many different ways you can accomplish this task.

You may find the Preview.app icon in the Dock at the bottom or side of your screen. You should find the Preview.app among all your application icons displayed by the Launchpad. Alternatively you can look for the Preview program in the Applications folder on your hard disk.

Preview application showing File menu.
When the Preview application is running look for the Preview menu in the top left corner of your screen. In the File menu select Open.
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Normally your digital photographs should be stored in the Pictures folder listed on the left side of this window. Here I have found the photo file in my Downloads folder. I can either double mouse click on the file to open it or I can click once on the file and then on the Open button.
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Here is my photograph that I want to resize. It is a picture of the backyard behind an old house.
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In the Tools menu along the top of the screen I found the command Adjust Size.
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Here is the window we need to resize the photograph. Make sure there is a checkmark in front of Scale proportionally. Make sure the Width and Height boxes are connected by a solid line and a locked padlock. You can investigate what photographic dimensions are listed in Fit into.
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When doing some research I found that 1024 pixels along the longest edge is often recommended as a good size for photographs that will be displayed on computer screens or the Internet. ( Computers love photograph dimensions that are multiples of eight. 1024 = 8 x 8 x 8 x 2 )

Since Width is the longest side I have changed it to 1024 pixels. The Preview application automatically changes the Height measurement.

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Oh no my photograph has shrunk! Which is exactly what I wanted it to do.
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In the View menu at the top of the screen there are some Zoom commands that can make the photo appear larger or smaller on the screen. The command Actual Size is the one I selected for this photo. Zoom to Fit would have been my second choice.
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Here is my resized photograph. Now I just have to find a way to save or export it while giving it a new filename.
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In the File menu along the top of the screen choose the Export command.
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Here is what the Export window looks like when you choose JPEG as the file type. I have changed the filename to yard1024 for my new file.
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Here is what the Export window looks like when you choose Tiff as the file type.
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Here is the final screenshot of this lesson showing the pixel dimensions of my original photograph file and the smaller resized photograph file we just created.