The answer lies in a common misunderstanding of the word "convert." When experts and high-end optimization tools talk about "PNG to PNG better," they do not mean changing the file type. They mean an existing PNG file to produce a better version of itself.

Digital cameras and editing software embed extra data into PNGs, such as the date created, camera model, GPS coordinates, and color profiles (like sRGB). Removing this metadata can instantly shrink a file by 10% to 30% without changing the image look.

Lossless compression reduces file size by rewriting the image data more efficiently and stripping out hidden baggage. It does not alter the pixels or image quality in any way.