About JPG to PNG
Converting JPG to PNG is straightforward, and it is worth being clear at the outset about what it does and does not achieve — because this particular conversion is surrounded by a persistent misunderstanding.
It will not improve your image. PNG is lossless, but lossless means "stores what it is given exactly", not "restores what was thrown away". The detail a JPG lost was discarded permanently when the JPG was first created. Converting to PNG stores those already-degraded pixels faithfully, usually at three to eight times the file size, with no visual improvement whatsoever. If an image looks soft or blocky, this conversion cannot fix it. Only a better original can.
So when is it the right move? Three cases, all legitimate.
*You are about to edit the image repeatedly.* Every time a JPG is opened, changed and re-saved, it is re-compressed and loses a little more. Ten rounds of that is visibly damaging. Converting to PNG first freezes the current quality: further saves cost nothing. This is the strongest reason to make the conversion.
*Something you are feeding it to requires PNG.* Some print workflows, older design software, icon pipelines and certain APIs simply will not take a JPG.
*You need to add transparency.* You cannot recover transparency that was never there — a JPG has none — but converting to PNG gives you an alpha channel to work with in an editor afterwards.
What you get. Identical pixels, a larger file, and no further generational loss. Dimensions, colour and content are unchanged; only the container differs.
One thing to watch. Because PNG files are so much larger, converting a folder of photographs can turn a few megabytes into a few hundred. That is expected rather than a fault, but it is worth knowing before converting a large batch on a device with limited storage.
If your goal is a *smaller* file rather than a lossless one, this is the wrong direction — WebP will give you a smaller file than either format while supporting transparency.
Conversion runs in your browser; nothing is uploaded.
Questions
Will this improve my JPG quality?
No. The detail was lost when the JPG was created. PNG stores the degraded pixels losslessly at a larger size — there is no visual gain.
Why would I convert to PNG then?
Mainly to stop further loss before repeated editing, to satisfy software that requires PNG, or to get an alpha channel you can edit into.
Why is the PNG so much bigger?
Lossless compression cannot discard the JPG artefacts and noise, so it has to store all of it exactly. Three to eight times larger is normal.
Are my images uploaded?
No. Everything happens in your browser.