Screenshot

A screenshot, screen dump, or screen capture or screenie 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. As of Mac OS X 10.4, pictures are no longer saved as PDF. They are saved as PNGs.
Screen capture : Capturing the screen over an extended period of time to form a Video file.

Uses of screen captures

It has become popular in the internet fandom culture to use screen captures (usually referred to as "screencaps") of movies and television shows in the creation of fanart, most commonly as icons for LiveJournal or MSN Messenger. Websites and LiveJournal communities have been created for the distribution of these screencaps, and they are generally greatly sought after as "capping" is considered to be a respectable and time consuming hobby.

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.

Mac OS

In all versions of Mac OS up through (and past) Mac OS 9 the user simply hits ⇧⌘3 (shift-apple key-3), this puts a PICT file of the screen on the desktop. ⇧⌘4 allows the user to make a marquee selection of the screen. The screen capture is accompanied by a sound effect of a camera shutter as it takes a picture (Grab, detailed below, continues this tradition).

Mac OS X

Mac OS X offers several means to take a screenshot :

using key combinations in the finder :

- shift - apple key - 3 will capture the full screen, and place files on the desktop. If you work in a multi-screen configuration, one file will be created for each screen.

- shift - apple key - 4 will allow you to capture part of the screen : after pressing those three keys, your cursor will become a small cross, and you will be able to select the region of the screen to capture. If you press the space bar, the cursor will become a camera, that will capture a window, a menu, the menu bar, an icon ... The item to capture will be highlighted as you pass your mouse over it.

If you press the control key (ctrl) while taking the screenshot, the resulting image will go to the clipboard instead of a file. You can then paste it in whatever program you want.

In Mac OS X v10.4 "Tiger", the files created using this method are png files by default. It is possible to change this, but it requires using the command line interface : in the Terminal, type :

defaults write com.apple.screencapture type image_format

where image_format could be BMP (Windows bitmap), GIF, JPEG 2000, JPEG, PDF, PICT, PNG, PSD, SGI, TGA & TIFF.

using some other applications :

- The application Grab supports one more option : timed screen capture.

- Preview version 3 (Mac OS X v10.4) now has an option to take window, selection and timed screen captures.

Both Grab & Preview automatically save the files as TIFF.

- many commercial programs can be used, that adds functions like capturing a video of the screen.

Screenshots cannot be taken while protected DVDs are playing in DVD Player.

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. You can then paste the clipboard into a program like MS Paint or Paint.NET to save it as an image file (for posting online, for instance), or paste it directly into a document. If saving as an image file, it is best to use a format which uses lossless compression (e.g. PNG) (or no compression, e.g. BMP). Use a format which supports 24-bit color if the screenshot contains many colors.

A Step-by-Step Guide

To copy the screen to the clipboard, press the Print screen key (normally located in the top row on the right-hand side of the keyboard).
If you wish capture only the active window, press and hold the Alt key, then press the Print screen key.
You may wish to paste (Ctrl-V) the screenshot into a word-processing program, such as Microsoft Word, for inclusion in your document.
However, a standard image format is smaller and generally better for distribution. To save as an image:
1. Click the "Start" button (normally located in the bottom left of your screen), and then click "Run".
2. Type "mspaint" (without quotes), and press "Enter." This opens Paint.
  Alternatively, you can go to (in Windows XP) Start --> All Programs --> Accessories --> Paint.
3. Press Ctrl-V to paste the screenshot. (In older versions of Paint, a dialog to resize the image may appear; click "Yes.")
4. Press Ctrl-S to open the Save As dialog box. Type a filename in the "File name" field.
  For "Save as type," select either "24-bit Bitmap", "TIFF", or "PNG". ("GIF" and the other three bitmap types are often not suitable for full-color screenshots because they discard color information; "JPEG" is never suitable for screenshots because it blurs borders.)
  Press "Enter" or click "Save" to save the screenshot.

Hardware overlays

Screenshots of games and media players sometimes fail, resulting in a blank rectangle. The reason for this is that the graphics are bypassing the normal screen and going to a high-speed graphics processor on the graphics card called the hardware overlay. Generally, there's no way to extract a computed image back out of the graphics card, though software may exist for special cases or specific video cards.

The trick to capturing those images is to turn off the hardware overlay. Because many computers have no hardware overlay, most programs are built to work without it, just a little slower.

There are two ways to turn off the overlay. The usual way is to turn it off in the settings for the specific game or media player. Instructions for Windows Media Player, QuickTime, RealPlayer and Winamp are here.

One can also turn off the hardware overlay globally through Windows as shown here. On Windows XP, go to Display Properties > Settings Tab > Advanced Button > Troubleshoot Tab. Set the Hardware Acceleration slider to one of the first three notches.

Store bought DVDs are a special case because they're encrypted using a patented algorithm called Content-scrambling system (CSS). Many DVD-capable media players (including Windows Media Player), but not all (PowerDVD, WinDVD, and Media Center to name a few), will only play DVDs on the overlay layer, where they can't be captured. For a review of which media players are best for screen capture, go here.

Scroll capture

Often a page or list doesn't show on your screen all at once, you must scroll to see it all. To capture those areas intact, use the scroll capture tool offered by some vendors. This tool captures the entire page or list, automatically scrolling vertically and/or horizontally as required.

Screen recording

The screen recording capability of some screen capture programs is a time-saving way to create instructions and presentations, but the resulting files are often large. For tips on managing the file size, with examples of the effects of each setting, go here. The professional way to create small, efficient demos is to build them from scratch in a Macromedia Flash editor, such as SwiSH Max., but this takes much more work.

Some sophisticated screen recording programs minimize file size by capturing only frames that change. In practice, you end up manually adding frames and doing other editing, so these programs fall mid-spectrum between simple recorders and building from scratch. One popular screen recording application that makes use of this is Camtasia Studio, by means of the proprietary TSCC codec.

A common problem with video recordings is the action jumps, instead of flowing smoothly, due to low frame rate. Though getting faster all the time, ordinary PCs are not yet fast enough to play videos and simultaneously capture them at professional frame rates, i.e. 30 frame/s. For many cases, high frame rates are not required. This is not generally an issue if simply capturing desktop video, which requires far less processing power than video playback, and it is very possible to capture at 30 frames/s. This of course varies depending on desktop resolution, processing requirements needed for the application that is being captured, and many other factors. For tips on maximizing frame rates, go here. For those who must have frame rates of 30 or above, one safe solution (though lower in overall quality) is to point a camcorder at the screen or to record on a VCR connected to the TV-Out on your graphics card.

X Window System

Since X Window System itself is not a desktop environment and only includes a very basic set of programs, methods of taking screenshots vary greatly on the platform. While xwd(1) is the closest "standard" way to do it in the X Window System, most people use other bundled utilities to achieve the task due to their ease of use.

xwd

On systems running the X Window System the standard utility to dump an image of an X Window is xwd(1), xwd produces an XWD image. 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 ^*. When run remotely, xwd is useful for taking screen shots of modal menus in action. The GIMP can be used to convert an XWD file to other more common formats such as PNG; equivalently, the command-line utility xwdtopnm, part of the Netpbm utility suite, can be used to convert the XWD file to PNM format, from which it can be converted to any common format.

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 (in GNOME versions older than 2.10), by selecting "Take Screenshot" from the "System..." menu (GNOME 2.10 or greater), by using the screenshot applet or by using one of the following two keyboard shortcuts:

Print Screen, to take a screenshot of the entire screen, or
Alt + Print Screen, to take a screenshot of the currently active window.

This can also be configured in Preferences → Keyboard Shortcuts.

ImageMagick

The import command from the widely used ImageMagick suite can be used for creating screenshots. A simple command to capture the screen is

import -window root screenshot.png

Screenshot software

There are many third-party programs available on different platforms 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, areas of the screen not visible on the monitor (autoscroll), and so on.

Video screen captures

None of the big operating systems have built-in mechanisms to record videos of the screen (recording how the user moves his mouse around, clicks icons, types text etc. as a movie). A multitude of utilities have come up to fill this void, though.

OS X

Third-party utilities to do video screen captures include Snapz Pro X (versiontracker info), Screentool (info) and ScreenBroadcasting (info).

Windows

Video screen capture tools include Capture Professional Fraps ^*.

Linux

Video screen capture tools include vnc2swf (GPL) ^*.

Copyright issues

Some companies believe the use of screenshots is an infringement of copyright on their program. This is one of the issues "solved" by Trusted Computing. Under Trusted Computing, programs will be able to block the taking of screenshots of their windows. Countering this argument is the principle of fair use, which (in U.S. law) permits copying of images or text for 'criticism, comment, news reporting, teaching, scholarship, or research.'

External links

WritersUA - Review of Screen Capture Tools (Updated December 2005)

Graphical user interface

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