Convert an image to any format
For when you know what you have and what you need, and it is not one of the common pairs. The source format is read from the file's own bytes, and the target list only ever offers formats this browser can genuinely produce.
Questions
Why don't I see AVIF in the list?
Because this browser cannot encode it. Image KB Reducer probes for real encoder support by encoding a one-pixel image and checking what actually came back, rather than guessing from the browser's name — and it never offers a format the encode would then fail on. Support is not where most people expect: WebKit encodes AVIF from a canvas, Chromium and Firefox do not.
Can I convert TO HEIC?
No. Image KB Reducer reads HEIC — iPhone images import fine — but no browser can encode it, so it is never offered as a target.
Where did the quality slider go?
You picked PNG. PNG is lossless and has no quality setting to move, so the slider is hidden rather than left there doing nothing. Image KB Reducer runs lossless oxipng optimisation on PNG output instead.