2 HEIF Image Format
iOS 11 introduces a new image format called HEIF, short for High Efficiency Image Format. This means that Apple will replace the industry standard JPEG format for images with a more efficient image format that is referred to as HEIF. Now when you take photos in iOS 11, they’ll be saved in HEIF format, which has a better image quality and takes up much less space, approximately half the size of JPEG images.
This is a major improvement for iOS as it allows users to store twice as many photos as they want with HEIF format. If you’re worried about how you’d share your HEIF images with devices that don’t support it, then the good news is that HEIF images are automatically converted to JPEG when you share them.
You can enable HEIF by going Settings > Camera > Formats and choosing High Efficiency format. Under the Most Compatible format, images will be saved as JPEG.