Images can be quite big depending on their resolution and file format. Professional photographers often rely on external storage devices or cloud storage to maintain their portfolios. For ordinary users, the quality of an image is rarely a big deal except of course when it comes down to the size. Images can be compressed to take up less space. The result is an image that looks more or less the same to an ordinary user but has lost some pixels in the compression process. A good compression tool won’t leave you with anything too pixelated. If you want to compress a JPEG on macOS, we recommend using Preview to do the job.
Preview can compress an image exceptionally well. That’s not to say that high compression will not leave you with some loss in quality, it will. In fact, if you compress an image as much as Preview allows you to, you may end up with image tearing. That said, Preview outshines most other image compression apps for macOS regardless of the level of compression you apply.
Compress a JPEG on macOS
Open the image in Preview. Preview can convert an image to JPEG so if your image is a PNG or a TIFF, the process for converting and compressing it in JPEG format will be the same.
With the image open, go to File>Export on the menu bar. In the Export box, select the JPEG format from the Format dropdown. When you select JPEG, a slider for Quality will appear. The slider will set the quality anywhere between ‘Best’ visually, and ‘Least’ visually. As you move the slider, Preview will calculate the new file size. Each mark on the slider indicates a decrement of 10%. We compressed an image to 30% and its size went from 2.5MB to 654KB.
Click Save and a copy of the image will be saved.
Once the compressed image has been saved, it’s a good idea to compare it with the original to see how much the quality has degraded. At 30% compression, the difference is rather obvious. If you think the image quality has suffered too much, you can compress the original image again but at a higher rate.
We compared Preview’s compressed images with a few commonly used compression tools for macOS and it did better in all tests. If you have an image compression tool that you want to try, compare it with Preview.
Things to look at when comparing the compressed images are tearing and the final file size. An image, once compressed cannot be restored to its original quality. Do not delete the original image unless you’re sure you won’t need it again.