What's a PNG?
PNG is the acronym for Portable Network Graphics, a digital standard for image files. The PNG is not as popular as the JPG standard, but the PNG boasts "lossless" quality from no compression. This supports maintaining better image quality by digital photography enthusiasts who wish to make multiple edits.
The PNG is a high quality file, but lack of compression means the file may be sized up to ten times larger than the same image saved as a JPG. This same lack of compression allows the PNG image file to retain it's quality over multiple color changes, croppings, and other edits to the image.
Great for Editing
Many enthusiasts capture digital photos as JPG files, and then convert to a PNG file to better support editing. Once the image is perfectly set, these same enthusiasts will then convert the file to a compressed JPG file to support more expedient file sharing. It can be helpful to think of JPG images as "viewing version" of a photo while the PNG image is more like a "work in progress".
How It Compares
A PNG image file is similar to the TIFF (Tagged Image File Format), which also supports "lossless" editing. However the TIFF image format supports other features that make it even more suited for use by graphics artists and the publishing industry that require an image file to also store raster graphics. PNG, TIFF, and JPG digital image files are all accessed using a similar technology.
PNG is the perfect image format for making multiple edits to your favorite photos. You can choose a variety of PNG image resolutions, with higher resolutions resulting in larger files. The 300 dpi (dots per inch) standard is a perfectly acceptable resolution for viewing files on most digital screens, but 600 dpi quality is better on larger displays, and 1200 dpi supports even finer editing.
The PNG digital image file is extremely resilient and moves across the world at the speed of light. As digital data, it can be copied and stored in multiple locations, further increasing its life expectancy to what one might consider indelible. This has lead to a worldwide digitizing boom and race to scan and forever save old printed photographs, negatives, and slides.