How to shrink your Mac screenshots

If you take a lot of screenshots on your Mac, you are likely filling up your computer, email, and your colleague’s email boxes with enormous files. This is because the default screenshot format on Mac is PNG, a nearly 30-year-old file format that doesn’t take advantage of modern advances in file compression techniques. What if I told you that there was a setting you could flip that would make future screenshots one-fifth or even one-tenth the size without sacrificing any noticeable quality?

How to take a screenshot on Mac

First, a quick refresher on how to take screenshots on Mac. There are many ways, depending on what you want to capture. Apple has a comprehensive overview of the process, but below is a quick description of the shortcuts. Unless you have changed the default location, screenshot files are saved to your Desktop.

• Shift-Command-3: Captures the entire screen

• Shift-Command-4: Captures a portion of the screen; click and drag from one corner to the opposite corner, creating a box

• Shift-Command-4, followed by the Spacebar: Captures a single window; just click the window you want to capture which will be highlighted in blue

• Shift-Command-5: loads the Screenshot app which allows you to use a menu to select options such as type of capture, video capture, add a delay, and choose the output location or app, such as directly inserting the screenshot into an email without first saving it.

If you aren’t good with memorizing shortcuts, you may want to locate the Screenshot app in Applications > Utilities and drag it to your Dock.

Your screenshot format options

You’ll need to decide which screenshot format option will work best for you.

• PNG. The default format. This format has some advantages. It’s a non-lossy format, which means that you can zoom in and each pixel will be 100% the original quality of the screen you captured. This is probably ideal if you are capturing screenshots for a high-quality production that must appear absolutely perfect.

  • Storage size: Enormous (A full-screen 4K image is about 10 megabytes)

  • Compatibility: Universal

  • Clarity: Perfect

• JPG. This is the format I would recommend for most people. JPG (or JPEG) is a common format that takes roughly one-fifth the storage space as PNG. It achieves this by analyzing the image and dropping information it considers unimportant (such as two pixels next to each other that are almost exactly the same color might be changed so they are the same color). It does this in such subtle ways that you probably would never notice unless you zoom in to the pixel level and compare.

  • Storage size: small (A full-screen 4K image is about 2 megabytes)

  • Compatibility: Universal

  • Clarity: Almost indistinguishable from perfect

• HEIC. This is a very new format that is superior in every way to JPG, except that, because it is new, is not widely used outside of the Apple world yet. All Apple software since 2017 (macOS High Sierra and iOS 11) can read this format, and the version of Windows 11 released at the end of 2022 (22H2) can read this (or earlier if the user has installed a plugin to allow it). Many websites have not added capabilities to upload HEIC. This is best for people who take screenshots primarily for their own use or are comfortable with converting the images before sending them to people who might be using older software.

  • Storage size: tiny (a full-screen 4K image is about 1 megabyte)

  • Compatibility: only guaranteed on Apple devices, but becoming more common

  • Clarity: Almost indistinguishable from perfect

How to switch your screenshot format

Strangely, Apple has not included a button or switch in Mac that you can click to adjust this setting. It must be done in Terminal. If you are uncomfortable with this, you should get someone to help you. Do not try typing the commands below manually; you should copy and paste them.

1. Open Terminal (Applications → Utilities).

2. Paste one of these commands and press Return:

Use HEIC (smallest files):

defaults write com.apple.screencapture type heic; killall SystemUIServer

Use JPG (most compatible yet small):

defaults write com.apple.screencapture type jpg; killall SystemUIServer

Go back to PNG (the default):

defaults write com.apple.screencapture type png; killall SystemUIServer

There will be no confirmation of the change, but you should not see an error message. Close the Terminal app, and you’re done—new screenshots will use your chosen format. Apple’s built-in screenshot tools continue to work the same way; you’re just changing the file type they save.