Convert decodes your source image in a Web Worker via createImageBitmap, draws it to an OffscreenCanvas, and re-encodes it to whichever of JPEG, PNG, or WebP you picked — the three formats verified as real, working encode paths in this browser, not a longer list assumed to work.
The size comparison you see is real, computed from the actual input and output byte counts — not an estimate. HDR preservation status is reported honestly: if the source carries a gain map, the badge says NOT PRESERVED, in plain terms, rather than a vague or optimistic label.
This is the same conversion pipeline the Optimize tool builds on — Optimize adds resizing and a genuine EXIF-preservation option on top of the identical decode/encode logic, rather than duplicating it.
Questions people actually ask
Will converting preserve my image's HDR data?
No — and Convert says so directly, every time, rather than staying quiet about it. Converting decodes the source to a flat bitmap and re-encodes it in the new format, which structurally can't carry a gain map through. If your source has one, use Encode afterward to add HDR headroom back to the converted file.
Which output format should I actually pick?
WebP is the reasonable default for web delivery — it beats JPEG at a given visual quality and PNG on file size for most content, and it's supported everywhere that matters today. Pick JPEG or PNG specifically when a downstream tool or pipeline you don't control needs one of those two. See the full JPEG vs. PNG vs. WebP comparison for the actual trade-offs.
Why is my converted file bigger than the original?
Usually because the source format and target format handle compression differently — converting a heavily-compressed JPEG to lossless PNG, for instance, will almost always produce a larger file, since PNG can't discard the detail JPEG already threw away, and now has to store it losslessly. Check the real before/after size comparison Convert shows you rather than assuming.
Does Convert support AVIF output?
Not yet — AVIF encode support isn't something we've verified this browser can do locally, so it isn't offered as an output option here. AVIF decode is supported (you can upload an AVIF file to convert from), just not encode to.