If you need to convert from one graphics format to another, you need the aptly named GraphicConventer from Lemke Software. It's recently been revved to version 10.4.2, and supports image conversion from over 200 graphic file formats into almost 80 different file formats.
Features in GraphicConverter include: support for 16-bit per channel grayscale raw import; split red/green/blue batch; a batch function to extract all used keywords to convert&modify; an option to disable indicator for unapplied xmp changes; zoom support to slideshow with gesture; dialog upon click of rotation indicator; a rating tool to image window toolbar; an option to open a browser with a default path upon launch; an option to use EXIF preview as browser thumbnail; the ability to import old picture clippings at 64 bit; the ability to import old StartupScreen variants; and editable number fields for display of slider values.
And, of course, Graphic Converter 10 has all the features of its predecessors. Exif creation verifies gps tags before export. The keyword palette supports import of plain keywords list. Next/previous icons use the last display scale for the new image. And more.
GraphicConverter 10.4.2 requires macOS 10.9 or higher. It's available from Lemke Software online and at the Mac App Store. The cost is $39.95 for a single user version and $59.95 for a family license.