subimages, the optimizations can be applied to them as well. At least one icon editor, Pixelformer, is able to perform a special optimization pass while saving ICO files, thereby reducing their sizes. FileOptimizer (mentioned above) can also handle ICO files. Icons for macOS may also contain PNG subimages, yet there isn't such tool available. See also Computer graphics, including: Image editing Image file formats Related graphics file formats APNG Animated PNG JPEG Network Graphics (JNG) Multiple-image Network Graphics (MNG) Similar file formats X PixMap for portable icons Scalable Vector Graphics WebP Explanatory notes References Further reading External links PNG Home Site libpng Home Page The Story of PNG by Greg Roelofs Test inline PNG images More information about PNG color correction The GD-library to generate dynamic PNG-files with PHP PNG Adam7 interlacing Encoding Web Shells in PNG files: Encoding human readable data inside an IDAT block. Computer-related introductions in 1996 Graphics standards Image compression ISO standards Open formats Raster graphics file formats World Wide Web Consortium standards