Xv is a shareware program by John Bradley for the display and manipulation of digital images, the X11 runs on most Unix-like operating systems.
The program has been very popular in the early 1990s and was a long time the most important image viewer on Unix systems. Due to copyright problems, the latest official version 3.10a was released in December 1994. Bradley did not make it to negotiate a license for the LZW algorithm, which is necessary to decode the then commonly used image format GIF.
However, Bradley has collected until at least 2000, third-party extensions to expand in this way the functionality of xv. The main improvements include support of the PNG image format. The extensions have been published only in the form of patches, which are sequentially applied to the original source code from 1994. Additional extensions are still (2007) created and maintained by volunteers.
Xv is invoked either from the command line with a variety of different possible arguments or just through a graphical interface. Most of the other image viewers and editors, the program is distinguished by the low consumption of computational resources and an efficient user interface. This is because many operations are combined within individual dialogs. Instead of making many individual changes, numerous parameters can be adjusted within the powerful dialogues, acting instantaneously on the displayed image. These include: making cut-outs, change the colors or applying filters. All changes of the dialogues en bloc be undone. Many common tools such as the changing individual pixels or drawing lines, however, are not implemented.
Xv is still present in current issues of Slackware and openSUSE, but is no longer included in most distributions of Linux. John Bradley is also the author of the available in the most common Linux distributions xcalc program.