Lossless optimization: same pixels, smaller file
PNG stores pixels with lossless DEFLATE compression, but how well a file compresses depends entirely on the effort the original encoder spent. Screenshot tools, export pipelines and most software libraries prioritize speed, so they leave real savings on the table. This tool runs oxipng, a modern Rust optimizer, which retries the file with better scanline filters, stripped metadata and a stronger compressor, then keeps the smallest result. Because it never touches the pixel values, it is safe for anything where accuracy matters: UI screenshots headed for documentation, logos, medical or scientific figures, and assets under design review. Typical savings run 10 to 40%. If you also have photos in JPG form, the lossy Compress JPG tool saves far more on those, and Compress Image handles mixed batches in one pass.
When converting beats compressing
Lossless optimization has a ceiling. If your PNG contains a photograph, that ceiling is very low: camera images are full of gradients and sensor noise that lossless compression cannot squeeze, so a 4 MB photo-in-PNG might only drop to 3.5 MB here. The fix is to change formats, not to compress harder. PNG to JPG re-encodes the photo lossily and typically lands at a tenth of the size with no visible difference, while PNG to WebP goes smaller still and keeps transparency if you need it. A good rule: if the image came out of a camera or looks like one, convert it; if it is a screenshot, chart, logo or anything with text and sharp edges, keep it as PNG and optimize it losslessly on this page. Either way the work happens on your own machine and your images stay private.
Common questions
Does compressing a PNG reduce its quality?+−
No. PNG optimization here is fully lossless: oxipng only rewrites how the pixel data is packed inside the file, trying better filter strategies and stronger DEFLATE compression. The decoded image is mathematically identical to the original, pixel for pixel. You will see a quality slider in the interface, but PNG output stays lossless regardless; the slider only matters for lossy formats like JPG and WebP.
How much smaller will my PNG get?+−
Typically 10 to 40%, depending on how unoptimized the source was. Screenshots from macOS or Windows, quick exports from design tools and images saved by libraries often use fast, lazy compression settings, so they have the most headroom. A PNG that was already run through a good optimizer may only shrink a few percent, because lossless compression has a hard mathematical floor.
My PNG is a photo and barely shrinks. What should I do?+−
PNG is the wrong container for photographs: lossless compression cannot exploit the smooth gradients and noise in camera images, so photos stored as PNG are huge and optimize poorly. Convert them instead. PNG to JPG typically cuts a photo by 80 to 90%, and PNG to WebP does even better for web use. Keep PNG for screenshots, text, logos and anything with sharp edges or transparency.
How does this compare to TinyPNG?+−
TinyPNG shrinks PNGs further because it is lossy: it reduces the color palette, which can subtly band gradients. It is excellent at that, but its free tier caps at 20 images of 5 MB each, and files upload to their servers. This tool is strictly lossless, has no caps of any kind, and runs oxipng in your browser so nothing is uploaded.