Lossless PNG compressor

Before you start

A lossless PNG compressor reduces file size by rewriting the image data more efficiently. It does not remove visible detail, change pixel dimensions, flatten transparency, or alter the aspect ratio. Lossless compression is suitable for screenshots, interface graphics, diagrams, logos, and other PNG files where exact pixels matter.

Decide whether you want a local tool or an online service. Local software processes files on your device, which avoids uploading images to a website. Online PNG compression tools can be convenient, but you should check how the service handles uploads, retention, and deletion before submitting private or sensitive images.

Step-by-step instructions

The exact menus depend on the tool, but the workflow is similar across common lossless PNG compressors.

• 1. Open the PNG file in a lossless-capable compressor.
• 2. Keep the output format set to PNG rather than converting to JPEG or WebP.
• 3. Select lossless, maximum compression, or a similarly named setting. Avoid options labeled lossy, reduced colors, or optimized for web.
• 4. Keep features such as transparency and the original pixel dimensions enabled unless you intentionally want to change them.
• 5. Save the result as a new file so the original remains available for comparison.

If the tool has compression effort or optimization level controls, a higher level may produce a smaller file but take longer to finish. The settings may also be named differently between versions, so check the option description rather than relying on a single label.

Check the output

Compare the compressed file with the original at full size. Lossless compression should show no visible difference, including in fine text, thin lines, and edges around transparent areas.

Confirm the pixel dimensions and aspect ratio are unchanged. If the file uses transparency, open it over a contrasting background to make sure that alpha information is still present. Some viewers may display transparency differently, so a changed preview does not by itself prove that the PNG data was altered.

File size reduction varies by image. A PNG with large flat areas often compresses more than a noisy photo-like image. If the file does not shrink, the image may already be efficiently encoded, or the compressor may not be using a lossless mode.

Common problems and next steps

One common issue is accidentally saving in a lossy format or selecting a reduced-color mode. If text becomes fuzzy or colors shift, reopen the tool and check whether a lossless or exact-color option is available.

For documents, screenshots, or images containing private information, prefer a local compressor over an online service. If you use a web-based compressor, review its privacy and file-handling terms before upload and remove or avoid source files that should not leave your device.

If the result is larger than expected, save the original again with lossless settings or try another PNG optimizer. Keep a copy of the uncompressed file until you have verified the output carefully.