The web is gaslighting your design workflow. Most websites use aggressive compression and CSS scaling to save bandwidth, hiding the high-resolution original behind a pixelated thumbnail. When you "Save Image As," you aren't getting the truth. RUS (Real Uncompressed Size) is a surgical Chrome utility that identifies the true original source file of any web image—bypassing the resizing filters and delivering the 100% uncompressed 4K/FHD resolution directly to you.