Interlaced video

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Interlaced video (also known as Interlaced scan) is a technique for doubling the perceived frame rate of a video display without consuming extra bandwidth.wikipedia
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Deinterlacing

deinterlacedeinterlacedDe-interlacing
To display interlaced video on progressive scan displays, playback applies deinterlacing to the video signal (which adds input lag).
Deinterlacing is the process of converting interlaced video into a non-interlaced or progressive form.

Field (video)

fieldfieldsvideo field
The interlaced signal contains two fields of a video frame captured consecutively.
When the fields are displayed on a video monitor they are "interlaced" so that the content of one field will be used on all of the odd-numbered lines on the screen and the other field will be displayed on the even lines.

DV

MiniDVDVCAMDVCPRO
It is still included in digital video transmission formats such as DV, DVB, and ATSC.
Closely following ITU-R Rec. 601 standard, DV video employs interlaced scanning with the luminance sampling frequency of 13.5 MHz.

Progressive scan

progressiveprogressive videoprogressive-scan
Interlaced scan refers to one of two common methods for "painting" a video image on an electronic display screen (the other being progressive scan) by scanning or displaying each line or row of pixels. New video compression standards like High Efficiency Video Coding are optimized for progressive scan video, but sometimes do support interlaced video.
This is in contrast to interlaced video used in traditional analog television systems where only the odd lines, then the even lines of each frame (each image called a video field) are drawn alternately, so that only half the number of actual image frames are used to produce video.

Broadcast television systems

broadcast television systembroadcast TVbroadcast
To prevent flicker, all analog broadcast television systems used interlacing.
All analog television systems are interlaced: alternate rows of the frame are transmitted in sequence, followed by the remaining rows in their sequence.

1080p

Full HDFHD1080p30
They recommend 720p 50 fps (frames per second) for the current production format—and are working with the industry to introduce 1080p 50 as a future-proof production standard.
Studies from 2009 show that for digital broadcasts compressed with H.264/AVC, transmission bandwidth savings of interlaced video over fully progressive video are minimal even when using twice the frame rate; i.e., 1080p50 signal (50 progressive frames per second) actually produces the same bit rate as 1080i50 signal (25 interlaced frames or 50 sub-fields per second).

ATSC standards

ATSCdigitalATSC standard
It is still included in digital video transmission formats such as DV, DVB, and ATSC.
The formats are listed here by resolution, form of scanning (progressive or interlaced), and number of frames (or fields) per second (see also the TV resolution overview at the end of this article).

Flicker (screen)

flickerflickeringscreen flicker
This enhances motion perception to the viewer, and reduces flicker by taking advantage of the phi phenomenon.
Televisions use interlaced video so the screen flickers at twice the rate (50 or 60 Hz) that the image changes (25 or 30 Hz).

Display lag

control latencyinput lag
To display interlaced video on progressive scan displays, playback applies deinterlacing to the video signal (which adds input lag).
For interlaced video, additional processing is frequently applied to deinterlace the image and make it seem to be clearer or more detailed than it actually is.

PAL

colour television25pPAL-N
A Phase Alternating Line (PAL)-based television set display, for example, scans 50 fields every second (25 odd and 25 even).
NTSC is used with a frame rate of 60i or 30p whereas PAL generally uses 50i or 25p; both use a high enough frame rate to give the illusion of fluid motion.

IBM 8514

85148514/AIBM 8514/A
Most modern computer monitors do not support interlaced video, besides some legacy medium-resolution modes (and possibly 1080i as an adjunct to 1080p), and support for standard-definition video (480/576i or 240/288p) is particularly rare given its much lower line-scanning frequency vs typical "VGA"-or-higher analog computer video modes.
IBM 8514 is an IBM graphics computer display standard supporting a display resolution of 1024x768 pixels with 256 colors at 43.5 Hz (interlaced; 87 fields per second), or 640x480 at 60 Hz (non-interlaced).

Léon Theremin

Leon ThereminLev Sergeyevich TermenLev Termen
In the domain of mechanical television, Léon Theremin demonstrated the concept of interlacing.
He also devised the interlace technique for improving the quality of a video signal, still widely used in video and television technology.

High Efficiency Video Coding

HEVCH.265H.265/HEVC
New video compression standards like High Efficiency Video Coding are optimized for progressive scan video, but sometimes do support interlaced video.
HEVC was designed with the idea that progressive scan video would be used and no coding tools were added specifically for interlaced video.

405-line television system

405-line405-lines405 line
Using interlace, a pair of 202.5-line fields could be superimposed to become a sharper 405 line frame (with around 377 used for the actual image, and yet fewer visible within the screen bezel; in modern parlance, the standard would be "377i").
The system used interlacing; EMI had been experimenting with a 243-line all-electronic interlaced system since 1933.

Moiré pattern

moirémoiremoire pattern
Interlace introduces a potential problem called interline twitter, a form of moiré.
This is due to interlaced scanning in televisions and non-film cameras, referred to as interline twitter.

High-definition television

HDTVhigh definitionHD
For instance, 1920×1080 pixel resolution interlaced HDTV with a 60 Hz field rate (known as 1080i60 or 1080i/30) has a similar bandwidth to 1280×720 pixel progressive scan HDTV with a 60 Hz frame rate (720p60 or 720p/60), but achieves approximately twice the spatial resolution for low-motion scenes.
All of these systems used interlacing and a 4:3 aspect ratio except the 240-line system which was progressive (actually described at the time by the technically correct term "sequential") and the 405-line system which started as 5:4 and later changed to 4:3.

NTSC

analogNTSC-M30p
The US adopted the 525 line system, later incorporating the composite color standard known as NTSC, Europe adopted the 625 line system, and the UK switched from its idiosyncratic 405 line system to (the much more US-like) 625 to avoid having to develop a (wholly) unique method of color TV.
The standard recommended a frame rate of 30 frames (images) per second, consisting of two interlaced fields per frame at 262.5 lines per field and 60 fields per second.

1080i

1080i501080i601080i25
For instance, 1920×1080 pixel resolution interlaced HDTV with a 60 Hz field rate (known as 1080i60 or 1080i/30) has a similar bandwidth to 1280×720 pixel progressive scan HDTV with a 60 Hz frame rate (720p60 or 720p/60), but achieves approximately twice the spatial resolution for low-motion scenes.
The "i" is an abbreviation for "interlaced"; this indicates that only the odd lines, then the even lines of each frame (each image called a video field) are drawn alternately, so that only half the number of actual image frames are used to produce video.

576i

625-line720x576analogue
The US adopted the 525 line system, later incorporating the composite color standard known as NTSC, Europe adopted the 625 line system, and the UK switched from its idiosyncratic 405 line system to (the much more US-like) 625 to avoid having to develop a (wholly) unique method of color TV.
The 576 identifies a vertical resolution of 576 lines, and the i identifies it as an interlaced resolution.

Refresh rate

refreshvertical scan rate120Hz
Interlacing provides full vertical detail with the same bandwidth that would be required for a full progressive scan, but with twice the perceived frame rate and refresh rate.
Similar to some computer monitors and some DVDs, analog television systems use interlace, which decreases the apparent flicker by painting first the odd lines and then the even lines (these are known as fields).

Mechanical television

Televisormechanicalelectromechanical television
In the domain of mechanical television, Léon Theremin demonstrated the concept of interlacing.
Meanwhile, in the Soviet Union, Léon Theremin had been developing a mirror drum-based television, starting with 16 lines resolution in 1925, then 32 lines and eventually 64 using interlacing in 1926, and as part of his thesis on May 7, 1926, he electrically transmitted and then projected near-simultaneous moving images on a five-foot square screen.

480i

480i60525 line525 lines
The US adopted the 525 line system, later incorporating the composite color standard known as NTSC, Europe adopted the 625 line system, and the UK switched from its idiosyncratic 405 line system to (the much more US-like) 625 to avoid having to develop a (wholly) unique method of color TV.
The 480 identifies a vertical resolution of 480 lines, and the i identifies it as an interlaced resolution.

Progressive segmented frame

PsF25PsF48 field per second (24 frame/s) video standard
Progressive segmented Frame (PsF, sF, SF) is a scheme designed to acquire, store, modify, and distribute progressive scan video using interlaced equipment.

John Logie Baird

BairdBaird TelevisionBaird Television Ltd.
As a result, this system supplanted John Logie Baird's 240 line mechanical progressive scan system that was also being trialled at the time.
His 600-line colour system used triple interlacing, using six scans to build each picture.

Standard-definition television

SDTVstandard definitionSD
The two common SDTV signal types are 576i, with 576 interlaced lines of resolution, derived from the European-developed PAL and SECAM systems, and 480i based on the American NTSC system.