psd A .psd extension file is an image file created with the help of Adobe Photoshop. PSD is the default extension used for saving a Photoshop Image which can have either a single or multiple layers which can be worked individually even after having saved the file. The file can also be saved in other formats like .jpg, .tiff, .gif or other imaging formats but if a user wants to edit the individual layers later, it is necessary to save the .psd file without overwriting it while converting it to another format. Converting a .psd extension file into an image file in another format flattens the image so that it can be viewed as a regular image. The images created using this extension are of a very high resolution and the quality in terms of clarity is extremely good as compared to other commonly used image formats like .jpg, .png or .bmp.
ppm The .ppm file extension is used for Portable PixMap format files and is intended to be an intermediate format that can be used in the development and conversion of other file formats. This format was specifically designed so that it could easily be exchanged between various platforms. It is very simple but not very storage efficient. Before the PPM format was introduced, Jef Poskanzer invented the PBM format in the year 1980 for transmission of monochrome bitmaps as ASCII text in email messages. He also developed a tool library for easy conversion of the PBM files to other graphical formats and vice versa. This library was called Pbmplus and was released in 1988. Later Poskanzer developed the PPM format along with the PGM format and the requisite tools that were added to Pbmplus.