Image formats differ in transparency, compression and compatibility. Choose the format required by the destination before optimising size.
Use JPEG for common photo uploads
JPEG is widely accepted and offers adjustable lossy compression. It has no alpha transparency, so transparent areas need a background colour. Repeated saves can degrade edges and fine detail. Keep an original when making multiple versions.
Use PNG for transparent graphics
PNG preserves sharp graphics and transparency with lossless pixel compression. A large photograph may become much larger as PNG. Exporting to PNG from a damaged JPEG preserves the current pixels; it does not undo earlier compression artifacts.
Consider modern web formats
WebP supports efficient photographic compression and transparency in modern browsers. AVIF can be efficient but takes more encoding work and is not accepted by every upload system. Our AVIF tool uses temporary server processing after consent.
Check the actual result
Do not change a filename extension to pretend a file uses another format. Export through a converter and reopen the file. Review colours, orientation, transparency and size. Browser re-encoding can omit the original metadata and colour profile.