DNG is an open-source raster image format developed by Adobe Systems and an extension of the TIFF 6.0 cross-platform universal format. The name of the format is an abbreviation of Digital NeGative Specification. The novelty was announced by the developer in 2004 as a standard format for RAW files. It is large in size because it contains not only the main image of high quality, but also metadata, as well as several images for preview (lower quality and resolution). Digital photos in this format are stored in uncompressed form.
PNG is a raster image format developed by PNG Development Group. The name PNG is an abbreviation for Portable Network Graphic. This image format is used primarily on the Internet for posting on web pages, since PNG files use Deflate compression without losing quality. The development of this format was undertaken in order to replace the GIF format, to which there were many complaints. PNG's image quality and specifications were much better, but unlike GIF, it does not support animation and uses the CMYK palette.