Lossless Image Compression | MiniPx — Free, Fast & Private
Lossless compression reduces file size without discarding any image data: every pixel in the output is identical to the original, and that is a property of the format, not a hope. A PNG stores its pixels behind a reversible compression stage, so a better encoder can pack the same pixels into fewer bytes while the decoded image stays bit-for-bit what it was. That is what matters for medical imaging, technical diagrams, screenshots with text, and any image where pixel-perfect accuracy counts.
PNG is the primary lossless format for web use. MiniPx optimizes a PNG by re-running that reversible stage with a stronger encoder — trying filters, colour types and bit depths that hold the same pixels in less space — and never by repainting a pixel. The only lossy option on this page is the explicit "Fewer colours" switch, which is off unless you turn it on.
Drop a JPEG, WebP or AVIF here and this page hands it straight back, unchanged, marked "Already optimal — left as-is". Those formats are already lossy, so re-packing them as a PNG would usually make the file larger, not smaller, and converting them here would break the promise the page is making. Metadata is still removed. If you want a smaller photo, the compressor on the home page is the right tool.
The trade-off is that lossless compression achieves smaller reductions than lossy compression. While lossy JPEG compression might reduce a photo by 80-90%, lossless PNG optimization typically achieves 10-30% reduction. The benefit is zero quality loss.
For photographs where minor quality loss is acceptable, lossy formats (JPEG, WebP) produce dramatically smaller files. Lossless compression is best reserved for graphics, screenshots, diagrams, and images that will be edited further.
MiniPx processes lossless compression entirely in your browser. No images are uploaded to any server — important when working with sensitive technical documents and medical images.
MiniPx normally decodes an image into memory before it can edit it, which caps input at 80 megapixels on this page. Lossless PNG-to-PNG recompression is different: it works on the file bytes directly and skips the decode step entirely, so MiniPx will attempt to losslessly recompress a giant scan or stitched panorama here as long as the PNG file itself is under 200 MB and you leave every colour in place, though an extremely high-resolution file can still fail to recompress even under that cap, on any device. A resize, a format change, or reducing colours (the "Fewer colours" option below) all still need a normal decode, so each of those stays capped at 80 megapixels like the rest of the page.