Resize and convert

Good to know

• The three maximum modes only ever shrink. Enlarging a small picture produces a bigger file with no more detail in it, so a 400 px image asked to fit 1920 px is left exactly as it was. "To an exact size" is the one that will stretch, and even then only with the proportions unticked.
• JPEG has no way to store transparency. Converting a PNG that has some fills it with the colour chosen above first — without that step the transparent parts come out black, which is the usual surprise.
• Quality only applies to JPEG and WebP, because PNG does not throw anything away. Below about 60 the losses start to show on flat areas and around text; between 75 and 85 is where most photographs sit.
• AVIF is missing on purpose: browsers read it but none of them will write it from a canvas. Asking for a format the browser cannot write does not fail — it quietly returns a PNG, so the result says which format actually came out.
• Photos are turned the way their orientation tag says before anything else happens, so a picture taken sideways comes out upright. Up to 20 MB per file, and everything happens in your browser — no image is uploaded anywhere.