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Progressive scan

A way to store and transmit images that draws all the lines in each frame in sequence. Compare to other techniques such as interlacing.

Progressive scanning (alternatively referred to as noninterlaced scanning) is a format 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.

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 need to introduce intentional blurring (sometimes referred to as anti-aliasing) 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 video games with this feature is the Super Smash Bros. series starting with Melee, where a "Deflicker" option exists. Ideally, it 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.

Progressive scan 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.

Key Terms

baird
frame
interlaced video
interline twitter
lines
noninterlaced scanning
progressive scan
progressive scanning
video
video games

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Progressive scan
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Last modified on May 19 2019
Content adapted from Wikipedia
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