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.
Image & Photo
Webpage / screenshot → image.
Capture a browser tab, window or screen and save one frame as a PNG.
1 Choose screen2 Preview3 Download
Capture what you can seeYour browser controls which tab, window or screen is shared.
Choose a tab, window or screen when your browser asks.
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.
Open the finished image at normal size and check crop, sharpness, dimensions and file size.
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.