Editing Screensaver (section)

== Purpose ==
=== Screen protection ===
Before the advent of [[LCD]] screens, most computer screens were based on [[cathode-ray tube]]s (CRTs). When the same image is displayed on a CRT screen for long periods, the properties of the exposed areas of the phosphor coating on the inside of the screen gradually and permanently change, eventually leading to a darkened shadow or "ghost" image on the screen, called a [[screen burn-in]]. Cathode-ray tube [[television]]s, [[oscilloscope]]s and other devices that use CRTs are all susceptible to [[phosphor burn-in]], as are [[plasma display]]s to some extent.<ref>{{Cite web |last=Phillips |first=Gavin |date=January 24, 2020 |title=How to Fix Screen Burn-In on TVs: Plasma, LCD, and OLED |url=https://www.makeuseof.com/tag/why-do-images-get-burned-into-lcd-and-plasma-displays-and-how-you-can-fix-it/ |url-status=live |archive-url=https://web.archive.org/web/20240126211617/https://www.makeuseof.com/tag/why-do-images-get-burned-into-lcd-and-plasma-displays-and-how-you-can-fix-it/ |archive-date=2024-01-26 |access-date=2022-09-18 |website=MakeUseOf.com |language=en-US}}</ref>

Screen-saver programs were designed to help avoid these effects by automatically changing the images on the screen during periods of user inactivity.

For CRTs used in public, such as [[automated teller machine|ATMs]] and railway ticketing machines, the risk of burn-in is especially high because a stand-by display is shown whenever the machine is not in use. Older machines designed without burn-in problems taken into consideration often display evidence of screen damage, with images or text such as "Please insert your card" (in the case of ATMs) visible even when the display changes while the machine is in use. Blanking the screen is not a valid option as the machine can be perceived as out of service. In these applications, burn-in can be prevented by shifting the position of the display contents every few seconds, or by having a number of different images that are changed regularly.

Later CRTs were much less susceptible to [[phosphor burn-in|burn-in]] than older models due to improvements in phosphor coatings, and because modern computer images are generally lower contrast than the stark green- or white-on-black text and graphics of earlier machines. LCD computer monitors, including the display panels used in [[laptop]] computers, are not susceptible to burn-in because the image is not directly produced by phosphors (although they can suffer from a less extreme and usually non-permanent form of [[image persistence]]).

=== Modern usage ===
[[File:Gnome-screensaver.png|thumb|[[GNOME Screensaver]] has an option for password protection.]]
While modern screens are not susceptible to the issues discussed above, screensavers are still used. Primarily these are for decorative/entertainment purposes, or for password protection. They usually feature moving images or patterns and sometimes sound effects.

As screensavers are generally expected to activate when users are away from their machines, many screensavers can be configured to ask users for a [[password]] before permitting the user to resume work. This is a basic security measure against another person accessing the machine while the user is absent.

Some screensavers activate a useful background task, such as a [[anti-virus software|virus scan]] or a [[volunteer computing]] application (such as the [[SETI@home]] project).<ref>{{Cite AV media |url=https://www.youtube.com/watch?v=IfeGNAZY92k |title=SETI@home Screensaver {{!}} Enhanced 5.27 |language=en |access-date=2022-09-18 |archive-url=https://web.archive.org/web/20220929181755/https://www.youtube.com/watch?app=desktop&v=IfeGNAZY92k |archive-date=2022-09-29 |url-status=live |via=[[YouTube]]}}</ref> This allows applications to use resources only when the computer would be otherwise idle. The [[Ken Burns effect|Ken Burns panning and zooming effect]] is sometimes used to bring the image to life.