Screenshot

From Sajun.org

A screenshot, screen dump, or screen capture is an image taken by the computer to record the visible items on the monitor or another visual output device, usually this is a digital image taken by the host operating system or software running on the computer device but it can also mean when a capture is made by an external device such as a camera or something intercepting the video output of the computer.

Screenshots, screen dumps or screen captures can be used to demonstrate a program, a particular problem a user might be having or generally when computer output needs to be shown to others or archived.

All three terms are often used interchangeably, however some people distinguish between them as follows:

Screenshot 
Outputting the entire screen in a common format such as PNG or JPEG.
Screen dump 
The display system dumps what it is using internally upon request, such as XWD X Window Dump image data in the case of X11 or PDF in the case of Mac OS X.
Screen capture 
Capturing the screen over an extended period of time to form a Video file.

Taking screenshots

There are numerous ways to take a screenshot on many operating systems, and applications. This article attempts to cover the ones that use standard software on each platform to achieve the task.

Microsoft Windows

In Microsoft Windows a screenshot of the entire monitor, complete with taskbar, can be copied to the system clipboard by pressing the Print Screen key. Alternatively, pressing ALT + Print Screen will copy just the active window to the clipboard.

There are many third-party programs available to take screenshots with advanced functionality. Most computer graphics software (e.g., IrfanView, GIMP, and Photoshop) can acquire screenshots. Typically, these programs can be configured to include or exclude the mouse pointer, automatically crop out everything but the client area of the active window, take timed shots, and so on.

Hardware overlays

Screenshots cannot be easily taken when hardware overlays are involved. Under such a setup, the operating system's video output function is bypassed in favor of more efficient low-level hardware functions that are handled by the graphics card or some other piece of specialized hardware. Hardware overlays are most frequently used for processor-intensive applications such as movies and games.

There are two main ways of getting around hardware overlays:

  1. Use a specialized screenshot-taking program configured to interface with the hardware itself. Such software is rare; many hardware overlays will not have screenshot programs written specifically for them. In fact, some hardware overlays are engineered in such a way that non-degraded screenshots are truly impossible.
  2. Configure the graphics driver to not use hardware optimization, at least until the desired screenshot is taken. This will likely result in decreased performance until hardware optimization is re-enabled.

Mac OS X

To save an image of the entire screen in Mac OS X pressing Command + Shift + 3 saves a PDF file on the desktop ( ~/Desktop/ ) containing a PDF Dump of the screen.

To take a picture of part of the screen, press Command + Shift + 4 and then select the area to be captured.

To take a picture of a window or menu, press the space bar after Command + Shift + 4. By default, the captures are stored in PDF on the desktop. To copy the captures to the clipboard, press the control key along with the other keys.

X Window System

Since the X Window System itself is not a desktop environment and only includes a very basic set of programs it is not common for the xwd(1) command to be used, most people use other bundled utilities to achieve the task.

xwd

On systems running the X Window System the standard utility to dump an image of an X Window is xwd(1), xwd produces XWD X Window Dump image data. It can be invoked in the following way:

xwd -root -out root.xwd

xwd can also be used to dump a single window if provided with the -id option followed by the corresponding window id, for further info see man 1 xwd [1]. When run remotely, xwd is useful for taking screen shots of modal menus in action.

ImageMagick

Alternatively if you have ImageMagick installed the following command can be used to import the root window and everything above to a PNG image file called root_window.png, it uses the convert(1) utility, you can take a screenshot of the entire contents of the screen with this command:

import -window root root_window.png

Alternatively you can use the import command without any arguments, you will then be presented with a cursor with which you can click on a window and the image generated will contain a image of that window only.

import root_window.png

KDE and GNOME

In the K Desktop Environment, the built-in program KSnapshot is the default screen grabbing utility.

GNOME users can take a screenshot either by selecting "Take Screenshot..." from the "Actions" menu or by using one of the following two keyboard shortcuts:

  • Shift + Control + right parenthesis, to take a screenshot of the entire screen, or
  • Shift + Control + left parenthesis, to take a screenshot of the currently active window.

The GIMP

The GIMP can also be used to take screenshots on any platform it is available on, simply navigate File->Acquire->Screenshot on the toolbox menu to capture either the current screen or choose timed mode.

See also

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