engineering

Low-definition television

Low-definition television is a engineering 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 Low-definition television rather than just read about it. In short: Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition television systems. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as low-definition analog television systems.

Key takeaways

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

Reference excerpt

Low-definition television (LDTV) refers to TV systems that have a lower screen resolution than standard-definition television systems. The term is usually used in reference to digital television, in particular when broadcasting at the same (or similar) resolution as low-definition analog television systems. Mobile DTV systems usually transmit in low definition, as do all slow-scan television systems.

Sources

The Video CD format uses a progressive scan LDTV signal (352×240 or 352×288), which is half the vertical and horizontal resolution of full-bandwidth SDTV. However, most players will internally upscale VCD material to 480/576 lines for playback, as this is both more widely compatible and gives a better overall appearance. No motion information is lost due to this process, as VCD video is not high-motion and only plays back at 25 or 30 frames per second, and the resultant display is comparable to consumer-grade VHS video playback. For the first few years of its existence, YouTube offered only one, low-definition resolution of 256x144 or 144p at 30~50 fps or less, later extending first to widescreen 426×240, then to gradually higher resolutions; once the video service had become well established and had been acquired by Google, it had access to Google's radically improved storage space and transmission bandwidth, and could rely on a good proportion of its users having high-speed internet connections, giving an overall effect reminiscent of early online video streaming attempts using RealVideo or similar services, where 160×120 at single-figure framerates was deemed acceptable to cater to those whose network connections could not sufficiently deliver 240p content.

Video games Older video game consoles and home computers often generated a technically compliant analog 525-line NTSC or 625-line PAL signal, but only sent one field type rather than alternating between the two. This created a 262 or 312 line progressive scan signal (with half the vertical resolution), which in theory can be decoded on any receiver that can decode normal, interlaced signals. Since the shadow mask and beam width of standard CRT televisions were designed for interlaced signals, these systems produced a distinctive fixed pattern of alternating bright and dark scan lines; many emulators for older systems offer video filters to recreate this effect. With the introduction of digital video formats these low-definition modes are usually referred to as 240p and 288p (with the standard definition modes being 480i and 576i). With the introduction of 16-bit computers in the mid-1980s, such as the Atari ST and Amiga, followed by 16-bit consoles in the late 1980s and early 1990s, like the Sega Genesis and Super NES, outputting the standard interlaced resolutions was supported for the first time, but rarely used due to heavy demands on processing power and memory. Standard resolutions also had a tendency to produce noticeable flicker at horizontal edges unless employed quite carefully, such as using anti-aliasing, which was either not available or computationally exorbitant. Thus, progressive output with half the vertical remained the primary format on most games of the fourth and fifth generation consoles (including the Sega Saturn, the Sony PlayStation and the Nintendo 64). With the advent of sixth generation consoles and the launch of the Dreamcast, standard interlaced resolution became more common, and progressive lower resolution usage declined. More recent game systems tend to use only properly interlaced NTSC or PAL in addition to higher resolution modes, except when running games designed for older, compatible systems in their native modes. The PlayStation 2 generates 240p/288p if a PlayStation game calls for this mode, as do many Virtual Console emulated games on the Nintendo Wii. Nintendo's official software development kit documentation for the Wii refers to 240p as 'non-interlaced mode' or 'double-strike'. Shortly after the launch of the Wii Virtual Console service, many users with component video cables experienced problems displaying some Virtual Console games due to certain TV models/manufacturers not supporting 240p over a component video connection. Nintendo's solution was to implement a video mode that forces the emulator to output 480i instead of 240p, however, many games released prior were never updated.

Teleconferencing LDTV Sources of LDTV using standard broadcasting techniques include mobile TV services powered by DVB-H, 1seg, DMB, or ATSC-M/H. However, this kind of LDTV transmission technology is based on existing LDTV teleconferencing standards that have been in place since the late 1990s.

Resolutions

Worked examples

Example 1 — a first encounter with Low-definition television

Start with the simplest possible case. Write down what Low-definition television claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 Low-definition television 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 Low-definition television 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 Low-definition television

In research: Low-definition television appears in engineering 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 Low-definition television 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: Low-definition television is common in secondary-school and first-year university syllabi. It links to neighbouring topics Broadband, Broadcast engineering, Digital television, so understanding it makes those chapters shorter.
In everyday life: Look for Low-definition television 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 Low-definition television in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Low-definition television 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 Low-definition television out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Low-definition television in simple terms?

Why does Low-definition television matter?

Because it connects several engineering 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 Low-definition television?

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 Low-definition television.