This describes how to convert graphics files from one type to another on a Mac. For example, if you have files created on your phone in HEIC format, you might want to convert them to JPEG to make them compatible for people on other platforms (after transferring them to your Mac).
These are the steps...
Find the file in the Finder (Desktop app). Double-click the file, which should open in Preview. If it opens in something else, close the file, go back to it in the Finder (Desktop app), right-click the file, choose "Open With" and choose "Preview" from the menu that appears. If Preview is not an option here, it means the file is either not a graphics file at all, or is in an obscure format which Preview doesn't know about. These files cannot be handled with this tip, but if another program appears in the "Open With" menu, you might be able to use that instead.
Once the file is open and displayed in Preview, hold down the option key, go to the "File" menu, and choose "Save As...". Rename the file if needed, but more importantly choose the format you want from the Format pop-up near the bottom of the Save window. Click "Save". Note that you can use the alternative option of duplicating and saving if you want to, but the option key trick is simpler.
The new file should appear in the same folder as the old file, which you can now delete if you want to.
Formats supported by Preview (current version, in Tahoe, and most older versions too) are: HEIC, JPEG, JPEG-2000, OpenEXR, PDF, PNG, and TIFF.
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