science

Scan conversion

Scan conversion 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 Scan conversion rather than just read about it. In short: Scan conversion or scan converting rate is a video processing technique for changing the vertical / horizontal scan frequency of video signal for different purposes and applications. The device which performs this conversion is called a scan converter.

Key takeaways

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

Reference excerpt

Scan conversion or scan converting rate is a video processing technique for changing the vertical / horizontal scan frequency of video signal for different purposes and applications. The device which performs this conversion is called a scan converter. The application of scan conversion is wide and covers video projectors, cinema equipment, TV and video capture cards, standard and HDTV televisions, LCD monitors, radar displays and many different aspects of picture processing.

Mechanisms and methods Scan conversion involves changing the picture information data rate and wrapping the new picture in appropriate synchronization signals. There are two distinct methods for changing a picture's data rate:

Analog Methods (Non retentive, memory-less or real time method) This conversion is done using large numbers of delay cells and is appropriate for analog video. It may also be performed using a specialized scan converter vacuum tube. In this case polar coordinates (angle and distance) data from a source such as a radar receiver, so that it can be displayed on a raster scan (TV type) display.

Digital methods (Retentive or buffered method) In this method, a picture is stored in a line or frame buffer with n1 speed (data rate) and is read with n2 speed, several picture processing techniques are applicable when the picture is stored in buffer memory including kinds of interpolation from simple to smart high order comparisons, motion detection and … to improve the picture quality and prevent the conversion artifacts.

How to realize The process in practice is applicable only using integrated circuits in LSI and VLSI scales. Timing, interference between digital and analog signals, clocks, noise and exact synchronization have important roles in the circuit. Digital conversion method needs the analog video signal to be converted to digital data at the first step. A scan converter can be made in its basic structure using some high speed integrated circuits as a circuit board however there are some integrated circuits which perform this function plus other picture processing functions like scissoring, change of aspect ratio and … an easy-to-use example was SDA9401.

Some examples

Up conversion (interpolation):

In many LCD monitors there is a native picture mode, however the monitor can display different graphical modes using a scan converter. In a 100 Hz/120 Hz analog TV, there is a scan converter circuit which converts the vertical frequency (refresh rate) from standard 50/60 Hz to 100/120 Hz to achieve a low level of flicker which is important in large screen (high inch) TVs. An external TV card receives the TV signals and converts them to VGA or SVGA format to display on monitor. Down conversion (decimation):

Many graphic cards have output for standard-definition television. Here there is a conversion from computer graphical modes to TV standard formats. Other graphic cards lack an SDTV output, but their VGA outputs can still be connected to an SDTV through an external scan converter (pictured). Scan conversion serves as a bridge between TV and computer graphics technology.

See also VESA Analog-to-digital converter Digital-to-analog converter International Telecommunication Union Video scaler

References

Television Engineering Handbook (K. Blair Benson) ISBN 0070047790 A technical introduction to digital video. (Charles A. Poynton) ISBN 047112253X Television and Video Systems. (Charles G. Buscombe) ISBN 013903014X Printed Circuits Handbook. (Clyde F. Coombs) ISBN 0070126097 Handbook of Filter Synthesis (Anatol I. Zverev) ISBN 0471986801

External links A/D, D/A Conversion for HDTV NTSC to VGA scan converter circuit Video Duplication with Access Scanning Scan Conversion Algorithms and techniques Fast polygon scan conversion with medical application

Worked examples

Example 1 — a first encounter with Scan conversion

Start with the simplest possible case. Write down what Scan conversion 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 Scan conversion 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 Scan conversion 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 Scan conversion

In research: Scan conversion 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 Scan conversion 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: Scan conversion is common in secondary-school and first-year university syllabi. It links to neighbouring topics Display technology, Television terminology, Video, so understanding it makes those chapters shorter.
In everyday life: Look for Scan conversion 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 Scan conversion in 20 minutes

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

Frequently asked questions

What is Scan conversion in simple terms?

Why does Scan conversion 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 Scan conversion?

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 Scan conversion.