What is a HEIC file?
HEIC is Apple's name for HEIF images compressed with HEVC, the same codec used for modern video. Since iOS 11, iPhones have saved photos in this “High Efficiency” format by default, because it keeps the same visual quality as JPEG in a noticeably smaller file.
On a Mac, HEIC just works: Photos, Preview and Finder open it without a second thought. The trouble starts when the photo leaves Apple's world. Many upload forms only accept JPG or PNG, older Windows PCs need an extra codec to open it, and most browsers other than Safari can't display it at all.
Why convert to JPG?
JPEG is the format everything understands: every browser, every email client, every printer kiosk, every CMS. Converting to JPEG trades a little efficiency for that universal compatibility. A JPEG is often slightly larger than the HEIC it came from, though Squeezels' mozjpeg encoder keeps the gap small, and with “Also compress” on the result can even come out smaller, as in the example above.
If the photos are going on a website, consider WebP or AVIF instead. Both are supported by every current browser and are far smaller than JPEG. Squeezels converts to those too.
Can't my Mac already do this?
It can, one way or another. Preview can export a single photo as JPEG, and the Photos app converts when you export. Those work for a photo or two. Squeezels is for when it's a whole folder, when you also want the files smaller, or when you want location data gone without thinking about it.
