Image work usually means one small change: a format a website will accept, a file under an upload limit, or dimensions that fit a layout. These tools do that decoding and re-encoding with the canvas APIs already built into your browser, so the picture never leaves your device. That matters for screenshots of internal dashboards, photos of documents, and anything else you would rather not hand to an anonymous upload form.

Common reasons to reach for these

A form rejects your file because it wants JPG or PNG specifically.
An image is a few megabytes over an attachment or upload limit.
A photo needs to fit a fixed width in a page, slide, or listing.
You saved a WebP from the web and something downstream cannot read it.

Lossy and lossless, briefly

PNG and WebP-lossless store exact pixels, so repeated saves never degrade. JPEG and lossy WebP discard detail your eye is unlikely to notice, which is why they are far smaller for photographs. Converting a JPEG to PNG stops further loss but cannot restore what the first JPEG pass already threw away, and it usually produces a larger file. Choose PNG for screenshots, flat colour, and transparency; choose JPEG for photographs.

What browser processing means for quality

Every conversion here decodes the image to a bitmap and re-encodes it. The browser's encoder decides the fine detail of that output, so a JPEG produced in Chrome and one produced in Safari at the same quality setting can differ slightly in size. Colour profiles attached to the original are not always carried through, so wide-gamut photographs can shift subtly. For colour-critical print work, use a dedicated editor.