The Portable Network Graphics Format is an image format that is most commonly used on the Internet today, in addition to JPEG. The PNG format was developed as a substitute for the GIF, which unfortunately could not be freely used in any graphics application due to license requirements.
PNG is license-free, which is why there are now numerous, even free software that can read and write this format. PNG compresses the graphics data with the lossless Deflate method, supports transparency, embedded gamma corrections, TrueColour, color palettes and color profiles. This makes PNG ideal for use on the Internet, especially when lossless graphics and images are required.
A replacement for the animated gif files was developed with MNG, which was not successful until now. Instead, an extension apng was created, which can now be displayed by some browsers. (Firefox 3 and Opera 9.5)
Although almost all graphics programs can generate PNG files, the compression rates are usually very different. Often PNG files are insufficiently optimized or padded with metadata, which makes the PNG files unnecessarily large. Some programs offer special options such as "save for web" or bring an extra application (such as Imageready in Photoshop). In some cases, the optimized saving functions can also be found under "Export" (eg Corel PaintShop Pro).
Pretty much any image viewer can display PNG images and since PNG is also a web format, of course, as well as any browser. It should be noted here that the Internet Explorer can only show the transparency of a PNG file as of version 7.