Progressive scanning (alternatively referred to as noninterlaced
scanning, and not to be confused with progressive download) 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, so that only half the
number of actual image frames are used to produce video. The system
was originally known as "sequential scanning" 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. Progressive scanning is
universally used in computer screens in the 2000s.
1 Interline twitter
2 Usage in storing or transmitting
3 Usage in TVs, video projectors, and monitors
4 See also
Interlaced video § Interline twitter
Interline twitter when the refresh rate is slowed by a factor of
three, demonstrated using the Indian-head test pattern.
This rough animation compares progressive scan with interlace scan,
also demonstrating the interline twitter effect associated with
interlacing. On the left there are two progressive scan images. In the
middle there are two interlaced images and on the right there are two
images with line doublers. The original resolutions are above and the
ones with spatial anti-aliasing are below. The interlaced images use
half the bandwidth of the progressive ones. The images in the center
column precisely duplicate the pixels of the ones on the left, but
interlacing causes details to twitter. Real interlaced video blurs
such details to prevent twittering, but as seen in the pictures of the
lower row, such softening (or anti-aliasing) comes at the cost of
image clarity. A line doubler shown in the bottom center picture
cannot restore the previously interlaced image to the full quality of
the progressive image shown in the top left one.
Note: Because the refresh rate has been slowed down by a factor of
three, and the resolution is less than half a resolution of a typical
interlaced video, the flicker in the simulated interlaced portions and
also the visibility of the black lines in these examples 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 DVDs, for example, as 480p24 or 576p25 formats. Progressive scan
was included in the Grand Alliance's technical standard for
the early 1990s. It was agreed that all film transmission by HDTV
would be broadcast with progressive scan in the US. Even if a
signal is sent interlaced, an
HDTV will convert it to progressive
Usage in TVs, video projectors, and monitors
Progressive scan is used for most cathode ray tube (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, few displays supported progressive-scan input. This
allowed these displays to take advantage of formats like PALPlus,
DVD players, and certain video game consoles. HDTVs
support the progressively scanned resolutions of
480p and 720p. The
1080p displays are usually more expensive than the comparable lower
HDTV models. At the debut of the 2010s UHD TVs had emerged
on the consumer market, also using progressive resolutions, but
usually sold with prohibitive prices – 4k HDTVs or were
still in prototype stage – 8k HDTVs. Prices for consumer
grade 4k HDTVs have since lowered and become more affordable, which
has increased their prevalence amongst consumers. Computer monitors
can use even greater display resolutions.
The disadvantage of progressive scan is that it requires higher
bandwidth than interlaced video that has the same frame size and
vertical refresh rate. Because of this
1080p is not used for
broadcast. 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.
The main advantage with progressive scan is that motion appears
smoother and more realistic. There is an absence of visual
artifacts associated with interlaced video of the same line rate, such
as interline twitter. Frames have no interlace artifacts and can be
captured for use as still photos. With progressive scan there is no
necessity in intentional blurring (sometimes referred to as
anti-aliasing) 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. Brawl,
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
It also offers clearer and faster results for scaling to higher
resolutions than its equivalent interlaced video, such as upconverting
480p to display on a
1080p HDTV. HDTVs not based on CRT technology
cannot natively display interlaced video, therefore interlaced video
must be deinterlaced before it is scaled and displayed. Deinterlacing
can result in noticeable visual artifacts and/or input lag between the
video source and the display device.
Progressive segmented frame: a scheme designed to acquire, store,
modify, and distribute progressive-scan video using interlaced
equipment and media
^ "Interlacing". Luke's
Video Guide. Archived from the original on
2014-02-22. Retrieved February 12, 2014.
^ Burns, R.W. John Logie Baird,
Television Pioneer, Herts: The
Institution of Electrical Engineers, 2000. 316.
^ Poynton, Charles A. (2003). Digital
Video and Hdtv: Algorithms and
Interfaces. Morgan Kaufmann. p. 56. ISBN 1558607927.
Retrieved 27 January 2013.
^ Abramson, Albert; Christopher H. Sterling (2007). The History of
Television, 1942 To 2000. McFarland. p. 245.
ISBN 0786432438. Retrieved 27 January 2013.
^ Hurley, Danny Briere (2008). Home Theater For Dummies. John Wiley
& Sons. p. 200. ISBN 0470444371. Retrieved 27 January
^ 4k resolution page, that includes a table of 4k display
devices with their corresponding prices. Retrieved 29 May 2013.
^ Sharp 8k TV launch, Displayed at CES 2013, the Sharp 8k UHD TV.
Retrieved 29 May 2013.
^ Zettl, Herbert (2011).
Television Production Handbook. Cengage
Learning. p. 94. ISBN 0495898848. Retrieved 27 January
^ Andrews, Dale (2011). Digital Overdrive: Communications &
Multimedia Technology 2011. Digital Overdrive. p. 24.
ISBN 1897507011. Retrieved 27 January 2013.
Broadcast video formats
System L (SECAM-L)
MPEG-4 AVC standards
MPEG-1 Audio Layer II
Digital cinema (DCI)
Display motion blur
Moving image formats
MPEG transport stream
Reverse Standards Conversion
Video on demand