A file viewer is an application software that presents the data stored in a computer file in a human-friendly form. The file contents are generally displayed on the screen, or they may be printed. Also, they may be read aloud using speech synthesis.
File viewer applications can be split into the following categories:
Such division of functionality was initially a result of software licensing for proprietary file formats, such as all file formats can be read freely but software license may exist that limits file creation and modification algorithms to be used only by licensor. For example, database software DBASE used proprietary algorithm for creating .DBF files, but Norton Commander had a built-in viewer for .DBF files. Acrobat Reader supports viewing of .PDF files, but another software application such as Microsoft Word or Adobe Photoshop is required to create .PDF files.
File viewers have to have sufficient knowledge about the file format to be viewed in order to handle different byte orders, code pages or newline styles. On contrary, media file viewers, such as Video Player applications may have initially very small number of file formats or none recognized, but rely on video codecs to play various media, making their capability to read and represent media file data to the user expandable.
Some file viewer may be classified as filters that translate binary files into plain text (one example antiword). However, depending on the competence of the translating routines, some information may be lost.
Image viewers display graphics files onscreen. Some viewers such as IrfanView are capable of reading multiple graphics file formats but some such as JPEGview are dedicated to a single format. Common image viewer features include thumbnail preview and creation, image zooming and rotation, color balance and gamma correction, resizing etc.
A web browser is a type of file viewer, which renders HTML markup into a human-friendly presentation. Although HTML is stored in plain text files, viewing an HTML file in a browser and in a text editor produces significantly different results. Web browsers may also be used to view image and multimedia files.
There are also types of data that are not intended for static display — these incorporate the time dimension. Viewers for such formats are named players. But the essence is the same — presenting file contents in human-friendly form (i.e. displaying video on the screen as intended, or playing sound through loudspeakers). And the same consideration of different file formats is present.