Compressing images is an essential task for many Mac users, whether preparing images for web posting, sharing photos via email or messages, or simply aiming to reduce file sizes for any other purpose.

There are several methods to compress images on a Mac, thereby decreasing their file size. We will demonstrate two straightforward techniques for achieving this in MacOS. Moreover, these methods can be combined for even greater image compression, significantly reducing file sizes. Let's explore these options.

Important Consideration on Image Compression

Compressing images effectively reduces file size, often substantially, but at the expense of image quality. Greater compression leads to lower quality, which is crucial to consider when balancing compression and quality.

Other image compression options exist that minimize quality loss while still reducing file size, such as removing EXIF and metadata, as discussed in this article. Additionally, mostly lossless compression methods like converting images to WebP are available, though WebP is not universally supported.

How to Compress Images on Mac Using Preview

Every version of MacOS includes the Preview app, a powerful yet often underutilized image editor. Preview offers built-in image compression functionality, which is simple to use. Here’s how:

1. Open the image you want to compress in the Preview app on your Mac (Preview is the default image editor, so double-clicking the photo or image will open it directly in Preview).

2. Go to the “File” menu and select “Export”.

3. Choose “JPEG” as the ‘Format’.

4. Focus on the “Quality” slider, where significant compression occurs. Typically, the optimal range is 75%-95% Quality. With about 80% compression, you can transform a 5MB image file into an 800kb file that appears nearly identical to most users!

5. Once satisfied with the compression, click “Save” to store the image at your chosen location.

In the example provided, an uncompressed 8 MB image of a flower was reduced to 1.6 MB by converting it to JPEG, and then further compressed to 532 KB using the image compression slider.

For even more effective compression, take the image saved from Preview and apply the next technique using ImageOptim.

Compress Images Losslessly with ImageOptim

ImageOptim is an excellent free tool for Mac users that employs various image compression algorithms to significantly reduce file size without compromising image quality. It also removes metadata and EXIF data, which is an added benefit.

1. Download ImageOptim for free to your Mac if you haven't already (available from the developer here).
2. Open ImageOptim on your Mac, then drag and drop the image(s) you want to compress into the ImageOptim window.
3. Allow ImageOptim to complete the compression process; the app will display the exact file size savings achieved by its algorithms.

ImageOptim works swiftly with most image file formats, though compressing a JPEG is faster than a PNG.

For optimal results, combine ImageOptim with other compression methods, such as converting an image to JPEG and then further refining compression to reduce file size even more. We have long appreciated this app for its no-frills, free, and user-friendly image optimization on Macs.

Following the original example, an 8 MB image of a flower was reduced to 488 KB, maintaining a quality that would appear identical to most people, unless closely examined in a photo editor like Photoshop or Pixelmator.

Image compression can be beneficial, especially when sharing images online or via email, as it significantly reduces file size, allowing for faster loading and transfer.

What tools or apps do you use for image compression? Do you utilize Preview on your Mac for compression by exporting to a different format like JPEG and adjusting the quality? Do you employ another method? Share your experiences and thoughts in the comments!

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