PNG is a lossless format, so a good compressor can shrink the file dramatically without touching how the image actually looks. The trick is throwing away hidden data your eyes never see — unused colors, bloated metadata and inefficient encoding — rather than crushing detail like JPG does. Here's how to do it in seconds, entirely in your browser, without uploading anything.
Yes. PNG uses lossless compression, so re-encoding it more efficiently — by removing unused colors from the palette, stripping metadata, and optimizing the DEFLATE stream — reduces the file size while keeping every pixel identical. You only lose quality if you switch to a lossy format like JPG or reduce the color depth below what the image needs.
PNGs balloon when they store a full 24/32-bit color table for an image that only uses a few colors (common with screenshots, logos and icons), or when they carry embedded metadata and color profiles. A compressor trims that overhead, which is why a 2MB screenshot can often drop to a few hundred KB with no visible change.
It depends on the tool. Most 'online' compressors upload your file to their servers. FileZap is different — all processing happens locally in your browser using the device's own canvas, so your images are never transmitted or stored anywhere. That makes it safe for IDs, screenshots and confidential graphics.