XCF is a file format from the raster graphics category developed by GIMP. The specified extension is considered the standard image format specifically for the GIMP graphics editor. In its characteristics, XCF is very similar to the PSD raster graphics format, which is native to Photoshop. XCF files do not support the function of saving the "history of cancellations", however, for other characteristics, they are highly praised by experts. So, they retain channels, transparency, layers, guides. Data compression in this format is lossless. The name of the format is associated with the organization of experimental computing (eXperimental Computing Facility) of the University of California, Berkeley.
PNM is a raster image category format. This is a bitmap bitmap created in Portable Any Map format. As you know, this format was intended from the very beginning to process some types of portable monochrome black and white images (PBM), color images (PPM) and grayscale images with shades of gray (PGM). Allows the inclusion of raster graphics data in the .PBM, .PGM or .PPM format. Such formats can provide an intermediate representation of data during the conversion of raster graphic files by different platforms. Separate applications support these three formats directly because they are defined as the PNM format. Able to be stored using binary data or ASCII text. PNM is the common format for the Netpbm package. It contains intermediate files that are used when it comes to converting several open source programs called Portable Bitmap. The PPM format was developed by J. Poskanzer. This is the easiest format for storing graphics. PNM files store one image. They do not apply compression. To view and process a bitmap image in PNM format, you can use programs such as GIMP, ImageMagick, Newera Graphics Converter Pro, XnViewMP. The same programs are able to convert images of this format.