In the prepress phase, an expert technician will review your files, manually and through preflight software, for any sign of a problem that may cause production errors. An electronic proof is issued once your PDF files pass the preflight inspection. If requested, hard copy proofs(for books and games) may also be created and sent to you for approval, usually for color purposes.
Once you have approved your proof and sent your files to press, your files are output through a process called the RIP (raster image processing). During this process, your images are separated into four colors, and output onto four metal printing plates.