![Screen-door effect](https://upload.wikimedia.org/wikipedia/commons/0/0e/Screen-door_effect.jpg)
The screen-door effect (SDE) is a
visual artifact
Visual artifacts (also artefacts) are artifact (error), anomalies apparent during visual representation as in digital graphics and other forms of imagery, especially photography and microscopy.
In digital graphics
* Image quality#Image quality f ...
of displays, where the fine lines separating
pixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device.
In most digital display devices, pixels are the smal ...
s (or
subpixel
In digital imaging, a pixel (abbreviated px), pel, or picture element is the smallest addressable element in a raster image, or the smallest point in an all points addressable display device.
In most digital display devices, pixels are the sm ...
s) become visible in the displayed
image
An image is a visual representation of something. It can be two-dimensional, three-dimensional, or somehow otherwise feed into the visual system to convey information. An image can be an artifact, such as a photograph or other two-dimensiona ...
. This can be seen in
digital projector
A video projector is an image projector that receives a video signal and projects the corresponding image on a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc lamp), X ...
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
A virtual reality headset (or VR headset) is a head-mounted device that provides virtual reality for the wearer. VR headsets are widely used with VR video games but they are also used in other applications, including simulators and trainers. VR ...
s and other
head-mounted display
A head-mounted display (HMD) is a display device, worn on the head or as part of a helmet (see Helmet-mounted display for aviation applications), that has a small display optic in front of one (monocular HMD) or each eye ( binocular HMD). An H ...
s, because these are viewed at a much closer distance, and stretch a single display across a much wider
field of view
The field of view (FoV) is the extent of the observable world that is seen at any given moment. In the case of optical instruments or sensors it is a solid angle through which a detector is sensitive to electromagnetic radiation.
Humans a ...
.
SDE in projectors
In LCD and DLP projectors, SDE can be seen because projector optics typically have significantly lower
pixel density
Pixels per inch (ppi) and pixels per centimetre (ppcm or pixels/cm) are measurements of the pixel density of an electronic image device, such as a computer monitor or television display, or image digitizing device such as a camera or image scanner. ...
than the size of the image they project, 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
A screen door can refer to a hinged storm door (cold climates) or hinged screen door (warm climates) covering an exterior door, or a screened sliding door used with sliding glass doors. In any case, the screen door incorporates screen mesh to blo ...
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 de
pixelization
Pixelization (British English, pixelisation) or mosaic processing is any technique used in editing images or video, whereby an image is blurred by displaying part or all of it at a markedly lower Image resolution, resolution. It is primarily u ...
, which used various optical methods to eliminate the visibility of the spaces between the pixels. The dominant method made use of a
microlens
A microlens is a small lens, generally with a diameter less than a millimetre (mm) and often as small as 10 micrometres (µm). The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects ...
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
Digital Light Processing (DLP) is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imaging ...
(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.
Newer DLP chip designs promise closer spacing of the mirror elements which would reduce this effect; 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.
See also
*
Rainbow effect
Digital Light Processing (DLP) is a set of chipsets based on optical micro-electro-mechanical technology that uses a digital micromirror device. It was originally developed in 1987 by Larry Hornbeck of Texas Instruments. While the DLP imagin ...
, an artifact associated with single-chip DLP projectors
*
Silk screen effect
The silk screen effect (SSE) is a visual phenomenon seen in rear-projection televisions. SSE is described by viewers as seeing the texture of the television screen in front of the image. SSE may be found on all rear-projection televisions includin ...
*
Scan line
A scan line (also scanline) is one line, or row, in a raster scanning pattern, such as a line of video on a cathode ray tube (CRT) display of a television set or computer monitor.
On CRT screens the horizontal scan lines are visually discernible ...
*
Subpixel rendering
Subpixel rendering is a way to increase the apparent resolution of a computer's liquid crystal display (LCD) or organic light-emitting diode (OLED) display by rendering pixels to take into account the screen type's physical properties. It takes ...
References
{{reflist
External links
Hi Fi Writer, "What is the 'screen door effect'?"
Display technology
Visual artifacts