PNGOUT is a freeware command line optimizer for PNG images written by Ken Silverman.

[4] PNGOUT was also available as a plug-in for the freeware image viewer IrfanView and can be enabled as an option when saving files.

[6] In 2006, a commercial version of PNGOUT with a graphical user interface, known as PNGOUTWin, was released by Ardfry Imaging, a small company Silverman co-founded in 2005.

[7] The main function of PNGOUT is to reduce the size of image data contained in the IDAT chunk.

Ken Silverman wrote a deflate compressor for PNGOUT that is slower than the ones used in most graphics software, but produces smaller files.