science

Progressive scan

Progressive scan is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Progressive scan rather than just read about it. In short: 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 ha…

Key takeaways

Progressive scan belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Progressive scan to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Progressive scan from memory before moving on to harder problems.

Reference excerpt

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 became universally used in computer screens beginning in the early 21st century.

Interline twitter

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 right picture cannot restore the previously interlaced image in the center to the full quality of the progressive image shown in the top left. Note: Because the refresh rate has been slowed 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 HDTV in the early 1990s. It was agreed that all film transmission by HDTV would be broadcast with progressive scan in the United States. Even if a signal is sent interlaced, an HDTV will convert it to progressive scan.

Usage in TVs, video projectors, and monitors Progressive scan is used for all LCD computer monitors and most HDTVs. Most cathode-ray tube (CRT) computer monitors and CRT-type displays, such as SDTVs, needed to use interlace to achieve full vertical resolution, but could display progressive video at the cost of halving the vertical resolution. Before HDTV became common, some televisions and video projectors were produced with one or more full-resolution progressive-scan inputs, allowing these displays to take advantage of formats like PALPlus, progressive scan DVD players, and certain video game consoles. Early HDTVs supported the progressively-scanned resolutions of 480p and 720p with 1080p displays available at higher cost. At the debut of UHD, TVs had emerged on the consumer market in the 2010s, 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.

Advantages 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 interlaced 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. 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.

See also 1440p Deinterlacing High Efficiency Video Coding Progressive segmented frame: a scheme designed to acquire, store, modify, and distribute progressive-scan video using interlaced equipment and media

References

Worked examples

Example 1 — a first encounter with Progressive scan

Start with the simplest possible case. Write down what Progressive scan claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Progressive scan before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Progressive scan ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Progressive scan

In research: Progressive scan appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Progressive scan in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Progressive scan is common in secondary-school and first-year university syllabi. It links to neighbouring topics Display technology, Television technology, Ultra-high-definition television, so understanding it makes those chapters shorter.
In everyday life: Look for Progressive scan outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Progressive scan in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Progressive scan means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Progressive scan out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Progressive scan in simple terms?

Why does Progressive scan matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Progressive scan?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Progressive scan.