Editing Line doubler

{{More references|date=December 2009}}
{{short description|Video technology}}
A '''line doubler''' is a device or algorithm used to [[deinterlace]] video signals prior to display on a [[progressive scan]] display.

The main function of a deinterlacer is to take an interlaced video frame which consists of 60 two-field interlaced fields of an [[NTSC]] [[analogue video]] signal or 50 fields of a [[PAL]] signal, and create a progressive scan output. 
<!--This will produce a picture with less visible scan lines.  The additional lines provide greater light output and makes for an image that is smoother and more film like.--> 
Cathode ray tube (CRT) based displays (both direct-view and projection) are capable of directly displaying both interlaced and progressive video, and therefore the line-doubling process is an optional step to enhance picture quality. Other types of displays are fixed pixel displays, including [[LCD]] displays, [[plasma displays]], [[Digital Light Processing|DLP]] projectors, and [[OLED]] displays, which are not scanned from top left to bottom right corners and generally cannot accept an interlaced signal ''directly'', and so require some kind of [[deinterlacing]]. Often, this is built in to the display and transparent to the user. Progressive scan DVD players also feature a deinterlacer.

Line doubling is a literal way to deinterlace an interlaced signal, although the method used may differ. Typically the use of the term "line doubler" refers to a simple repeat of a [[scanline]] so that the lines in a field match the lines of a frame. However, this produces a "bobbing" effect and has led to this method of deinterlacing being referred to as "bob deinterlacing". An iteration on bob deinterlacing is to average adjacent scanlines of two frames which can produce a smoother, although blurrier, image. This technique is referred to as "blend deinterlacing".
<!--Many line doublers instead use digital interpolation to recreate the missing lines in an interlaced signal, and the resulting quality depends on the technique used. Many line doublers interpolate within a single field, rather than merging information from adjacent fields, to preserve the smoothness of motion, resulting in a frame rate equal to the field rate, i.e. a normal 30 or 25 frames per second (60/50 fields per second) interlaced signal would be converted to 60 or 50 progressive frames per second.-->
Some line doublers are capable of using the former technique in moving areas and the latter in static areas (to avoid the "bob" effect), which improves overall sharpness.

Even if a line doubler employs the merging method it cannot be considered an inverse [[telecine]] device if a frame rate of 60p other than the original 24p is obtained. From this aspect of view some hyped progressive scan technologies (including Pioneer's PureCinema Progressive Scan) bearing an inverse telecine insignia are thus overstated.

Line doublers have been replaced recently by [[video scaler]]s which incorporate [[3:2 pulldown]] removal and the ability to scale the image to the various screen resolutions used on modern projectors and displays. However, line doublers such as the Open Source Scan Converter<ref>{{cite web |title=OSSC |url=http://junkerhq.net/xrgb/index.php?title=OSSC |publisher=Classic Console Upscaler wiki |accessdate=17 April 2020}}</ref> have been developed to convert signals from older [[video game consoles]] and have found popularity among [[Retrogaming|retro gaming]] enthusiasts due to their minimal contribution to [[input lag]].

==See also==
* [[3:2 Pulldown]]
* [[Deinterlacing]]

==References==
{{Reflist}}

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[[Category:Film and video technology]]


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