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 a 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.
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, progressive scan 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 resolution 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 an 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 the 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 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.
The 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.