How to Compress PNG on Mac: Preview, WebP, and Tools

To learn how to compress PNG on Mac devices quickly, the fastest built-in method is opening the file in Preview, selecting Tools > Adjust Size, and lowering the pixel dimensions or resolution. Because PNG uses lossless compression, standard Mac tools cannot simply drop the quality slider like they do for JPEGs without changing dimensions or converting the file format.

Which PNG compression method should you pick?

How you should shrink a PNG depends entirely on what the image contains and whether you need to keep a transparent background. Here is how the common scenarios break down:

• Keep transparency with the smallest file size: Convert the PNG to WebP. WebP preserves alpha transparency while reducing file size by 26% to 70% using modern lossy compression.
• Downsize without third-party software: Use macOS Preview to lower image dimensions. If a screenshot is 3840x2160 pixels, dropping it to 1920x1080 cuts the file size drastically.
• Photos saved as PNG: Convert them to JPG using macOS Quick Actions or Preview. PNG is the wrong format for photos; switching to JPG can cut a 12 MB PNG down to 800 KB instantly.
• Automating lots of files locally: Use the macOS Terminal with built-in command-line tools to process entire folders without uploading anything.

For immediate size reduction in your browser without uploading files to a remote server, you can use the free AtomnyX PNG compressor to re-encode or convert your graphics directly in memory.

Method 1: Compress PNG files in-browser with AtomnyX

The AtomnyX Compress PNG tool runs entirely in your browser using client-side processing, meaning your images are never uploaded to an external server. You can keep your transparency intact while achieving significant compression by converting to WebP at a quality setting that prevents visible artifacts.

1. Open the AtomnyX Compress PNG tool in Safari, Chrome, or any modern Mac browser.
2. Drag your PNG file directly into the browser window.
3. Choose WebP as your target format if you need to keep transparency while slashing file weight. Set the quality slider around 82 for general graphics, or 90 to 95 for logos with fine lines and text.
4. Click to export and save your compressed image back to your Mac.

If you regularly optimize assets for sites, you might also compare WebP vs PNG to see how compression ratios differ across graphics types, or use the dedicated PNG to WebP converter for full-batch workflows.

Method 2: Reduce PNG file size using Preview

Every MacBook and Mac desktop includes Preview. While Preview does not let you adjust the compression quality of a PNG directly, it allows you to shrink pixel dimensions, which is the most reliable native way to reduce large PNG files.

1. Double-click your PNG image to launch it in Preview (or right-click the file and select Open With > Preview).
2. Click Tools in the top menu bar, then click Adjust Size.
3. Ensure the Scale proportionally checkbox is checked so the image does not stretch.
4. Change the width or height to a smaller value. For instance, drop a 4000 px wide screen capture to 2000 px.
5. Review the "Resulting Size" estimate at the bottom of the window, then click OK.
6. Press Command + S to save the changes directly over the original file, or go to File > Export to save a new copy.

If you want to read more about native macOS image tools, see our guide on how to reduce image size on Mac using Preview and Finder.

Method 3: Convert PNG to JPG using Finder Quick Actions

If your PNG image does not have transparent elements, keeping it as a PNG wastes disk space and bandwidth. macOS includes a built-in Quick Action in Finder that converts files to JPG and applies adjustable compression levels.

1. Open Finder on your Mac and locate the PNG file you want to compress.
2. Right-click (or control-click) the image file.
3. Hover over Quick Actions and select Convert Image.
4. In the pop-up prompt, choose JPEG under the Format dropdown.
5. Choose an Image Size: Small, Medium, Large, or Actual Size. Selecting "Medium" often cuts file sizes by over 80%.
6. Click Convert to JPEG. macOS saves the new, compressed file directly beside your original PNG.

Keep in mind that converting to JPEG will turn transparent backgrounds into solid white. If transparency is mandatory, keep reading for lossless alternatives.

Method 4: Shrink PNG images via Mac Terminal

Mac power users can compress PNGs via the Terminal using sips (Scriptable Image Processing System), a tool shipped standard on macOS by Apple. This utility resizes files without opening an app window.

1. Press Command + Space, type Terminal, and hit Return.
2. Navigate to the directory holding your image (for example, type cd ~/Downloads).
3. Run the sips command to scale the image's maximum dimension down to 1200 pixels:
   sips -Z 1200 your-image.png
4. Check the file size in Finder; the PNG will be noticeably smaller because unnecessary pixel data was stripped.

Common PNG compression problems and fixes

Why is my compressed PNG the same size or larger?

PNG is strictly a lossless format. It does not possess a quality slider like JPEG or WebP. When a software program re-encodes a PNG, it passes the pixel array through its local PNG encoder. If your source file was already optimized, running it through a basic browser encoder can sometimes produce a file that is actually larger than your original. To get real file size cuts on stubborn PNGs, your best bet is converting to WebP (which preserves transparency) or JPEG (if transparency is unnecessary).

How to compress large PNG files without losing transparency

Do not export to standard JPEG. Instead, convert your image to WebP format. WebP supports full 8-bit alpha channels while running modern lossy compression algorithms. At a quality level of 82, files commonly shrink between 26% and 70% compared to original PNGs without visible degradation around edges or gradients. For vector graphics and icons, you can also explore SVG vs PNG to see if a vector format fits your design better.

Text and logo borders look blurry after compression

Standard compression algorithms designed for photos often smudge sharp geometric shapes and text. If you are compressing a corporate logo or UI asset, set your WebP compression quality between 90 and 95. At quality 92, the image will appear visually indistinguishable from the master file while cutting 40% to 60% of the byte weight.

Frequently Asked Questions

How to shrink PNG on Mac without installing software?

You can shrink a PNG by opening it in Preview, navigating to Tools > Adjust Size, and lowering the width or height values. Alternatively, right-click the file in Finder, choose Quick Actions > Convert Image, and export it as a JPEG if you do not need transparency.

How to make a PNG file smaller on Mac while keeping transparency?

To retain full alpha transparency while making the file substantially smaller, convert the PNG to WebP. You can process this without sending files across the internet using client-side tools like the AtomnyX Compress PNG tool, which maintains transparency while dropping file size by 26% to 70%.

Does reducing image resolution lower print quality?

Yes. If you change a 300 DPI (dots per inch) image to 72 DPI or drop its pixel dimensions, it will appear identical on screens but may look pixelated or blurry when printed on paper. Keep an uncompressed copy of your master file whenever you plan to produce physical prints.

Why are Mac screenshots so large by default?

macOS saves screen grabs as high-resolution PNGs tailored for Retina displays, packing twice as many pixels horizontally and vertically. A single full-screen capture on a modern MacBook can easily exceed 5 MB. Lowering the resolution in Preview or converting it to JPEG cuts this size down immediately.