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.
Colour & Accessibility
Live URL contrast scanner.
Capture a live browser tab and scan the screenshot for low-contrast neighbouring areas.
1 Choose screen2 Preview3 See scan
Scan a live pageYour browser controls which tab, window or screen is shared.
Capture the live page you want to scan.
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.
Use the number as a signal, then look at the real text size, weight, background and surrounding colours.
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.