PNG files are lossless compressed bitmapped images. While they are compressed, they can still attain large file sizes depending on the type of image data saved—they are best suited for images with large areas of solid colours and defined boundaries (such as logos). Unlike JPG files, they are not especially suited for storing photographic image data. Optimized PNG files are smaller than GIF files, and support higher-quality.
The following is a list of third-party compression tools that can be used to reduce the file size of a PNG file.
These tools provide the greatest file size savings, but will reduce the quality of the file as a consequence. Depending on the tool and the amount of compression used, the changes in quality may or may not be noticeable.
- TinyPNG is an online tool that uses lossy compression to reduce the file size of PNG images
- Way2enjoy is another online tool that uses same lossy compression to reduce the size of PNG, JPEG & GIF images
- ImageAlpha is a Mac tool that can reduce PNG files using pngquant, pngnq and posterization. You can often reduce size by 40-60% without noticeable loss in quality.
- pngquant is a command-line tool that can reduce large 24-bit PNG to small 8-bit PNG with full alpha transparency.
- CompressPNG is a tool that allows to reduce the palette size to any value between 2 and 256 colors
These tools don't lose any quality, they only re-compress images and remove invisible metadata:
- ImageOptim is a Mac based only image compressor
- PNGGauntlet is a Windows PNG image compressor
- Trimage is a Linux based image compressor
- Pngcrush is a command-line application that reduces the size of PNG files losslessly. The resulting image will be identical to the original visually, but can end up being much smaller. It can be downloaded from its sourceforge page at http://pmt.sourceforge.net/pngcrush/.