It changes the wrapper.
A file format is the way the same underlying media is packaged and encoded. Converting changes compatibility and storage behaviour more than it changes the subject itself.
Smart / Local Tools
Generate a mask for an object.
Detect the objects in an image, click the subject you want, refine the mask edge, then export either a black-and-white mask or a transparent PNG.
Tip: detection selects the area; segmentation separates the subject inside it. Thin edges, glass, fur and overlapping objects can still need a close check.
Private by design: both local models run in this browser. First use may download them.
Useful to know
Four things worth knowing.
Conversion is not enhancement.
Conversion is not enhancement. Re-encoding a poor source cannot restore missing detail, and some formats lose transparency, animation or metadata.
Check what the format dropped.
Automatic results still need a human check around edges, text, faces and small details.
Choose for what happens next.
Choose the format for what happens next: JPG for ordinary photos, PNG when transparency matters, WebP/AVIF for web delivery, and keep the source if you may edit again.