Progressive scan
Encyclopedia
Progressive scanning is a way of displaying, storing, or transmitting moving images in which all the lines of each frame
are drawn in sequence. 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.
The system was originally known as "sequential scanning" (a more technically correct description) when it was used in the Baird
240 line television transmissions from Alexandra Palace
, United Kingdom in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920s.
Note: Because the refresh rate has been slowed down by a factor of three, and the resolution is less than half that of typical interlaced video, the flicker in the simulated interlaced portions and also the visibility of the black lines in this image are exaggerated. Also, the images above are based on what it would look like on a monitor that does not support interlaced scan, such as a PC monitor or an LCD or plasma-based television set, with the interlaced images displayed using the same mode as the progressive images.
s, for example, as 480p24
or 576p25
formats.
(CRT) computer monitors, all LCD computer monitors, and most HDTVs
as the display resolutions are progressive by nature. Other CRT-type displays, such as SDTVs
, typically display interlaced video only.
Some TVs
and most video projectors have one or more progressive scan inputs. Before HDTV became common, some high end displays supported 480p
(480 horizontal lines of resolution with progressive scan). This allowed these displays to be used with devices that output progressive scan like progressive scan DVD player
s and certain video game consoles. HDTVs
support the progressively scanned resolutions of 480p and 720p. 1080p displays are available but are usually more expensive than the comparable lower resolution HDTV models. Computer monitors can use even greater display resolution
s.
The disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate
. For explanations of why interlacing was originally used, see interlaced video.
For an in-depth explanation of the fundamentals and advantages/disadvantages of converting interlaced video to a progressive format, see deinterlacing
.
Film frame
In filmmaking, video production, animation, and related fields, a film frame or video frame is one of the many still images which compose the complete moving picture...
are drawn in sequence. This is in contrast to interlaced video used in traditional analog television
Analog television
Analog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...
systems where only the odd lines, then the even lines of each frame (each image called a video field) are drawn alternately.
The system was originally known as "sequential scanning" (a more technically correct description) when it was used in the Baird
John Logie Baird
John Logie Baird FRSE was a Scottish engineer and inventor of the world's first practical, publicly demonstrated television system, and also the world's first fully electronic colour television tube...
240 line television transmissions from Alexandra Palace
Alexandra Palace
Alexandra Palace is a building in North London, England. It stands in Alexandra Park, in an area between Hornsey, Muswell Hill and Wood Green...
, United Kingdom in 1936. It was also used in Baird's experimental transmissions using 30 lines in the 1920s.
Example of interline twitter
This rough animation compares progressive scan with interlace scan, also demonstrating the interline twitter effect associated with interlace. On the left are two progressive scan images. Center are two interlaced images. Right are two images with line doublers. Top are original resolution, bottom are with anti-aliasing. The interlaced images use half the bandwidth of the progressive ones. The images in the center column precisely duplicate the pixels of the ones to the left, but interlace causes details to twitter. Real interlaced video blurs such details to prevent twitter, but as seen on the bottom row, such softening (or anti-aliasing) comes at the cost of image clarity. A line doubler could not restore the previously interlaced image at bottom center to the full quality of the progressive image on the top left.Note: Because the refresh rate has been slowed down by a factor of three, and the resolution is less than half that of typical interlaced video, the flicker in the simulated interlaced portions and also the visibility of the black lines in this image are exaggerated. Also, the images above are based on what it would look like on a monitor that does not support interlaced scan, such as a PC monitor or an LCD or plasma-based television set, with the interlaced images displayed using the same mode as the progressive images.
Usage in storing or transmitting
Progressive scan is used for scanning and storing film-based material on DVDDVD
A DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Panasonic in 1995. DVDs offer higher storage capacity than Compact Discs while having the same dimensions....
s, for example, as 480p24
480p
480p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixel high vertically scanning lines, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio or a horizontal resolution of...
or 576p25
576p
576p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced, the 576 for a vertical resolution of 576 lines, usually with a horizontal resolution of 720 or 704 pixels. The frame rate can be given explicitly after the letter.-576p25:In other...
formats.
Usage in TVs, video projectors, and monitors
Progressive scan is used for most Cathode ray tubeCathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRT) computer monitors, all LCD computer monitors, and most HDTVs
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
as the display resolutions are progressive by nature. Other CRT-type displays, such as SDTVs
Standard-definition television
Sorete-definition television is a television system that uses a resolution that is not considered to be either enhanced-definition television or high-definition television . The term is usually used in reference to digital television, in particular when broadcasting at the same resolution as...
, typically display interlaced video only.
Some TVs
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...
and most video projectors have one or more progressive scan inputs. Before HDTV became common, some high end displays supported 480p
480p
480p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixel high vertically scanning lines, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio or a horizontal resolution of...
(480 horizontal lines of resolution with progressive scan). This allowed these displays to be used with devices that output progressive scan like progressive scan DVD player
Progressive scan DVD player
A progressive scan DVD player is a DVD player that can output video in a progressive scan format such as 480p or 576p . Players which can output resolutions higher than 480p or 576p are often called upconverting DVD players....
s and certain video game consoles. HDTVs
High-definition television
High-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
support the progressively scanned resolutions of 480p and 720p. 1080p displays are available but are usually more expensive than the comparable lower resolution HDTV models. Computer monitors can use even greater display resolution
Display resolution
The display resolution of a digital television or display device is the number of distinct pixels in each dimension that can be displayed. It can be an ambiguous term especially as the displayed resolution is controlled by all different factors in cathode ray tube , flat panel or projection...
s.
The disadvantage of progressive scan is that it requires higher bandwidth than interlaced video that has the same frame size and vertical refresh rate
Refresh rate
The refresh rate is the number of times in a second that a display hardware draws the data...
. For explanations of why interlacing was originally used, see interlaced video.
For an in-depth explanation of the fundamentals and advantages/disadvantages of converting interlaced video to a progressive format, see deinterlacing
Deinterlacing
Deinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
.
Advantages of progressive scan
- Absence of visual artifacts associated with interlaced video of the same line rate, such as interline twitter.
- No necessity in intentional blurring (sometimes referred to as anti-aliasingAnti-aliasingIn digital signal processing, spatial anti-aliasing is the technique of minimizing the distortion artifacts known as aliasing when representing a high-resolution image at a lower resolution...
) of video to reduce interline twitter and eye strain.
- In the case of most media such as DVD movies and video games, the video is blurred during the authoring process itself to subdue interline twitter when played back on interlace displays. As a consequence, recovering the sharpness of the original video is impossible when the video is viewed progressively. A user-intuitive solution to this is when display hardware and video games come equipped with options to blur the video at will, or to keep it at its original sharpness. This allows the viewer to achieve the desired image sharpness with both interlaced and progressive displays. An example of a video game with this feature is Super Smash Bros. BrawlSuper Smash Bros. BrawlSuper Smash Bros. Brawl, known in Japan as , often abbreviated as SSBB or simply as Brawl, is the third installment in the Super Smash Bros. series of crossover fighting games, developed by an ad hoc development team consisting of Sora, Game Arts and staff from other developers, and published by...
, where a "Deflicker" option exists. Ideally, "Deflicker" would be turned on when played on an interlaced display to reduce interline twitter, and off when played on a progressive display for maximum image clarity.
- Offers clearer and faster results for scaling to higher resolutions than its equivalent interlaced video, such as upconverting 480p to display on a 1080p HDTVHigh-definition televisionHigh-definition television is video that has resolution substantially higher than that of traditional television systems . HDTV has one or two million pixels per frame, roughly five times that of SD...
.
- HDTVs not based on CRTCathode ray tubeThe cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
technology cannot natively display interlaced video, therefore interlaced video must be deinterlacedDeinterlacingDeinterlacing is the process of converting interlaced video, such as common analog television signals or 1080i format HDTV signals, into a non-interlaced form....
before it is scaled and displayed. Deinterlacing can result in noticeable visual artifacts and/or input lagInput lagDisplay lag is a phenomenon associated with some types of LCD displays, and nearly all types of HDTVs, that refers to latency, or lag measured by the difference between the time a signal is input into a display and the time it is shown by the display. This lag time has been measured as high as...
between the video source and the display device.
- Frames have no interlace artifacts and can be captured for use as still photos.
See also
- 240p
- 576p576p576p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced, the 576 for a vertical resolution of 576 lines, usually with a horizontal resolution of 720 or 704 pixels. The frame rate can be given explicitly after the letter.-576p25:In other...
- 288p
- 480p480p480p is the shorthand name for a video display resolution. The p stands for progressive scan, i.e. non-interlaced. The 480 denotes a vertical resolution of 480 pixel high vertically scanning lines, usually with a horizontal resolution of 640 pixels and 4:3 aspect ratio or a horizontal resolution of...
- 720p720p720p is the shorthand name for 1280x720, a category of High-definition television video modes having a resolution of 1080 or 720p and a progressive scan...
- 1080p1080p1080p is the shorthand identification for a set of HDTV high-definition video modes that are characterized by 1080 horizontal lines of resolution and progressive scan, meaning the image is not interlaced as is the case with the 1080i display standard....
- 1440p