Open the image you’d like to convert with Preview on your Mac (usually the default).How to convert PNG and TIFF images to JPG on Mac We’ll start by looking at how you can accomplish this with the built-in Mac app, Preview, then discuss some other options. If you’ve already got an image in a PNG, TIFF, or another format but need to convert it to JPG, there are a few ways to approach it. There are a variety of image formats you’ll come across, but one of the most common is JPG (JPEG). Need to save an image in another format? Follow along for how to convert images like PNG and TIFF files to JPG on Mac.