This tool changes an image's format, size and file weight — the three things that stand between a photo from a phone and a file some website will actually accept. Convert a HEIC-exported PNG to JPG for a form that only takes JPG, shrink a 4000-pixel photograph to the 1200 pixels a blog needs, or re-encode to WebP and watch the file drop by half at the same visible quality. Several images can be processed at once and arrive as a ZIP. The pictures are decoded and redrawn by your own browser, so they are never uploaded.
No. Each image is decoded by your browser, redrawn on a canvas and re-encoded on your device. Nothing is transmitted, and no copy is kept once you leave the page.
It depends on the source. A PNG photograph converted to JPG or WebP often drops by 80 percent or more; a JPG re-encoded at 80 percent quality typically halves; resizing to a smaller pixel size usually saves more than any format change. The table after conversion shows the exact numbers.
With PNG and WebP, yes. JPG has no transparency at all, so transparent areas are filled with white rather than turning black — if you need a transparent background, choose PNG or WebP.
Only if your browser can decode HEIC, which most desktop browsers cannot. Safari on Apple devices handles it; elsewhere, export the photo as JPG on the phone first and convert that.
With JPG and WebP, yes — each pass re-compresses what the previous pass produced, and small errors accumulate. Always convert from the original file rather than from an earlier conversion. PNG is lossless, so it can be re-saved freely.