What does converting PNG to JPG actually do?
PNG stores pixels losslessly, so an image survives any number of edit-and-save cycles without degrading, and it carries an 8-bit alpha channel for genuine transparency. That fidelity is why it is the standard for logos, icons, UI screenshots and any graphic with sharp edges or flat colour. JPEG discards detail the human eye is least likely to notice, which is why a photo can shrink by 80–90% with no obvious visual difference. The trade-offs are permanent: there is no alpha channel, and every re-save recompresses the image, so repeated editing slowly degrades it. Converting PNG to JPG therefore re-encodes the same content under a different set of rules — the pixels are decoded from the source image and written out through the destination encoder. Nothing is uploaded: the decode-and-re-encode cycle happens on your own machine.