Portable Network Graphics

Portable Network Graphics (.png) is an extensible file format for the lossless, portable, well-compressed storage of raster images. PNG provides a -free replacement for GIF and can also replace many common uses of TIFF. Indexed color, grayscale and RGB images are supported, plus an optional alpha channel. Sample depths range from 1 to 64 bits per pixel, supporting up to 48-bit RGB color with a 16-bit alpha channel.

Description
PNG is designed for online viewing applications, such as the World Wide Web, so it is fully streamable with a option. PNG is robust, providing both full file and simple. Also, PNG can store and  data for improved color matching on various platforms.

"Minified" PNGs
PNGs normally support alpha channels to support transparency at 8 or 16-bits per pixel. However, it is also possible to create a "minified" 8-bit indexed color image with a "cheap" alpha channel; though this format is supported in most modern web browsers, it has not been as widely supported by graphics software until relatively recently.

Online PNG tools

 * Compress PNG
 * PNG Compressor at Gift of Speed
 * PNG minifier at Photopea
 * TinyPNG