View source for Screen-door effect

{{Short description|Visual artifact of displays}}
{{more references|date=March 2014}}
{{Use dmy dates|date=March 2016}}
[[File:Screen-door effect.jpg|thumb|280px|right|Demonstration of the screen door effect]]
The '''screen-door effect''' ('''SDE''') is a [[visual artifact]] of displays, where the fine lines separating [[pixel]]s (or [[subpixel]]s) become visible in the displayed [[image]]. This effect can be seen in [[digital projector]] images and regular displays under magnification or at close range, but the increases in display resolutions have made this much less significant. More recently, the screen-door effect has been an issue with [[virtual reality headset]]s and other [[head-mounted display]]s, because these are viewed at a much closer distance, and stretch a single display across a much wider [[field of view]].<ref>{{cite web |url=https://techcrunch.com/2014/03/26/a-brief-history-of-oculus/ |author=Greg Kumparak |date=26 March 2014 |title=A Brief History Of Oculus |work=TechCrunch }}</ref>

== SDE in projectors ==
In [[LCD]] and DLP projectors, SDE can be seen because projector optics typically have significantly lower [[pixel density]] than the size of the image they project,{{Citation needed|date=March 2016}} enlarging these fine lines, which are much smaller than the pixels themselves, to be seen. This results in an image that appears as if viewed through a fine screen or mesh such as those used on anti-insect [[screen door]]s.

The screen-door effect was noticed on the first digital projector: an LCD projector made in 1984 by Gene Dolgoff. To eliminate this artifact, Dolgoff invented [[pixelization|de-pixelization]]{{Note to editors|this doesn't really look correct due to having a link mid-text. Someone should rephrase this}}, which used various optical methods to eliminate the visibility of the spaces between the pixels. The dominant method made use of a [[microlens]] array, wherein each micro-lens caused a slightly magnified image of the pixel behind it, filling in the previously-visible spaces between pixels. In addition, when making a projector with a single, full-color LCD panel, an additional appearance of pixelation was visible due to the noticeability of green pixels (appearing bright) adjacent to red and blue pixels (appearing dark), forming a noticeable repeating light and dark pattern. Use of a micro-lens array at a slightly greater distance created new pixel images, with each "new" pixel being a summation of six neighboring sub-pixels (made up of two full color pixels, one above the other). Since there were as many micro-lenses as there were original pixels, no resolution was lost, which was confirmed with modulation transfer function (MTF) measurements.

The screen-door effect on [[Digital Light Processing]] (DLP) projectors can be mitigated by deliberately setting the projected image slightly out of focus, which blurs the boundaries of each pixel to its neighbor.  This minimizes the effect by filling the black pixel perimeters with adjacent light.  Some older LCD projectors have a more noticeable screen-door effect than first generation DLP projectors.<ref>{{cite web | url=http://en.allexperts.com/q/Home-Theater-2859/dlp-versus-lcd.htm | date=18 May 2004 | title=Home Theater: dlp versus lcd | work=AllExperts | url-status=dead | archiveurl=https://web.archive.org/web/20131110003842/http://en.allexperts.com/q/Home-Theater-2859/dlp-versus-lcd.htm | archivedate=10 November 2013 | df=dmy-all }}</ref>  Newer DLP chip designs promise closer spacing of the mirror elements which would reduce this effect;{{cn|date=November 2013}} however, some space is still required along one edge of the mirror to provide a control circuit pathway. Use of Dolgoff's depixelization method could also produce a DLP projector without noticeable pixelation.<ref>{{Cite book |last=Dolgoff |first=Eugene |title=High-Resolution Displays and Projection Systems |chapter=Optical depixelization for electronic image projection |date=1992-07-01 |editor-last=Schlam |editor-first=Elliott |editor2-last=Slusarczuk |editor2-first=Marko M. |series=Proceedings of the SPIE |volume=1664 |pages=160–171 |doi=10.1117/12.60360|bibcode=1992SPIE.1664..160D }}</ref>

==See also==
* [[Pancake lens]]
* [[Digital Light Processing#The color wheel "rainbow effect"|Rainbow effect]], an artifact associated with single-chip DLP projectors
* [[Scan line]]
* [[Silk screen effect]]
* [[Subpixel rendering]]
* [[Uncanny valley]]
* [[Virtual reality sickness]]

==References==
{{reflist}}

==External links==
*[http://www.hifi-writer.com/he/video/screendoor.htm Hi Fi Writer, "What is the 'screen door effect'?"]

{{Extended reality|state=collapsed}}

[[Category:Display technology]]
[[Category:Visual artifacts]]
[[Category:Virtual reality]]