Make a photographic negative: every channel becomes 255 - value , so black turns white, blue turns orange, and back again if you run the result through a second time. Transparency is left alone. Drag the amount below 100% to stop part of the way.
At 50% every channel lands on the same mid-grey, so the picture disappears rather than half-inverting. The interesting values are near the top of the range.
The edit is redrawn on a canvas in this tab and re-encoded in the format you dropped — JPEG stays JPEG, PNG stays PNG, and anything else comes back as PNG. Nothing is uploaded.