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X

XBM
X Window System
x-y order

XBM

X BitMap. Filename extension for a bitmap for use with the X Window System.

X Window System

A specification for device-independent windowing operations on bitmap display devices, developed initially by M.I.T.'s Project Athena and now a de facto standard supported by the X Consortium. X was named after an earlier window system called "W". It is a window system called "X", not a system called "X Windows".

X uses a client-server protocol, the X protocol. The server is the computer or "X terminal" with the screen, keyboard, mouse and server program and the clients are application programs. Clients may run on the same computer as the server or on a different computer, communicating over Ethernet via TCP/IP protocols. This is confusing because X clients often run on what people usually think of as their server (e.g., a file server) but in X, it is the screen and keyboard etc. that are being "served out" to applications.

x-y order

An ordered set of visibility samples arranged according to descending absolute value of the spatial frequency coordinate u --- i.e., with |u| |u| ..... |u| ---is said to be in x-y order. This is a convenient ordering for performing the gridding convolution, but most imaging software no longer requires that the data be pre-sorted to this order, obtaining it, or an approximation to it, "on the fly".

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