Display technology

There are a wide variety of display tech­nologies ranging from inexpensive displays to high-end colour stereoscopic displays. There are some common characteristics that should be examined when matching a display to an application. They include

· The ability to display images as well as text.

· Resolution or quality of the image.

· Portability of the computer.

· The price of the display.

A video display is a subsystem that consists of two components: a display adapterand a display screen. The dis­play adapter acts as a channel of commu­nication between the computer and the display screen. It contains built-in video memory that stores the images for the display screen. The greater the complex­ity of the images to be displayed, the more memory required. It also contains its own processor, sometimes called a video coprocessor.

A display divides the screen into a grid of rows and columns. The intersection of a row and column on the screen is called a pixel, short for picture element. It is the smallest unit of display. Resolution re­fers to the number of pixels displayed across and down on the display screen. The more pixels on the screen, the finer the quality and detail of the image. An­other measure of resolution is the size of the pixel, called adot pitch. The smaller the pixels, the sharper the quality of the displayed image.

Aliasing. Because display images consist of pix­els arranged in rows and columns in­stead of continuous surfaces, the prob­lem of aliasing—the jagged or stair step appearance of the edges of diagonal lines or curves—must be resolved. Higher resolution solves part of the problem, but anti-aliasingtechniques have been developed that shade or colour neighbouring pixels along an edge to make the transition between light and dark less visible.

Video Graphics Array. Because of advances in display tech­nology, resolution continues to increase.. There are several stan­dard resolutions that have evolved to meet the needs of various applications. Video Graphics Array (VGA ),a standard developed by IBM in 1987, offers a minimum 640-by-480-pixel resolution.

VGA has been enhanced by a standard called Super VGA, which can display im­ages at two resolutions: 800 by 600 pix­els, and 1024 by 768 pixels.

Extended Graphics Array (XGA ), introduced in 1991, is an IBM extension of VGA that offers 1280-by-1024-pixel resolution and up to 32,768 simultaneous colours.

Ultra Extended Graphics Array (UXGA) supports resolution 1600x1200 pixels.

VGA resolution both use the same number of pixels, so the smaller image always looks better.

TYPES OF DISPLAYS

CRT Display. Video display can be accomplished by a cathode ray tube (CRT ), commonly used in television sets. Display on a CRT screen is accomplished by an electron beam that scans across and down the screen, and then returns to the upper left-hand corner to repeat the process. The technique leaves points of light on the inside phosphor-coated surface of the tube. The beam current is either increased to make a lighter point (pixel) or decreased to make a darker point (pixel) along each of the scan lines.

The display creates a complete image 80 times per second (80 Hz). A drawback to this refresh rate is that in many applications, the screen flickers causing eyestrain and fatigue. This problem can be eliminated by in­creasing the refresh rate (usually to 70 or 80 Hz) to create flicker-free images. Gen­erally, the higher the refresh rate, the higher the cost of the display.

CRTs use three separate elec­tron beams that represent the primary additive colours, red, blue, and green. The beams are focused so that their dot pat­terns slightly overlap on the screen to create the desired colours.

Nowadays CRTs are being ousted by liquid crystal displays (LCDs).

Liquid Crystal Displays (LCDs). The most common type of flat panel is the liquid crystal display (LCD)—a liquid-filled display surface that, when electrically charged, creates images us­ing ambient light. The historical drawback to LCDs has been their lack of clarity. Because early LCDs produced no light of their own but instead relied on reflected light for viewing, they had a very narrow range of viewing angles and could only be seen clearly if you looked at them straight on. To compensate for this deficiency, manufacturers are dealing with the problem in several ways. The first is to backlight the LCD by adding lights that shine through the LCD screen from be­hind, thus providing a clearer image. The second is to build LCDs with supertwistcrystals, which refract or twist the light to provide much higher con­trast (e.g., darker characters against a lighter background). Higher contrast also makes a wider viewing angle pos­sible when looking at the display. The third is to place a transistor at each pixel location on the display. This technique, known as active-matrix technology, produces a high-contrast display at the cost of consuming more power.

Active-matrix technology. Active-matrix LCDs depend on thin film transistors (TFT). Basically, TFTs are tiny switching transistors and capacitors. They are arranged in a matrix on a glass substrate. To address a particular pixel, the proper row is switched on, and then a charge is sent down the correct column. Since all of the other rows that the column intersects are turned off, only the capacitor at the designated pixel receives a charge. The capacitor is able to hold the charge until the next refresh cycle. And if we carefully control the amount of voltage supplied to a crystal, we can make it untwist only enough to allow some light through. By doing this in very exact, very small increments, LCDs can create a gray scale. Most displays today offer 256 levels of brightness per pixel.

Plasma displays Plasma display technology is a new emissive" flat panel technology which gives the rich accurate colour fidelity of conventional Cathode Ray Tube (CRT) monitors in a large plasma display that is thin enough to hang on the wall. It's the best way to achieve flat panel display with excellent image quality and large screen sizes viewable in any environment. This plasma display technology known as “ plasma vision " is an array of cells, known as pixels, which are composed of 3 sub-pixels, corresponding to the colours red, green and blue. Gas in plasma state is to react with phosphors in each sub-pixel to produce coloured light (red, green or blue). These phosphors are the same types used in conventional cathode ray tube (CRT) devices such as televisions and standard computer monitor displays. You get the rich, dynamic colours you expect from plasma display. Each subpixel is individually controlled by advanced electronics to produce over 16 million different colours.

TFT panels Using the latest technology such as PVA (patterned vertical alignment) TFT panels offer fast response time, 170-degree viewing angles, high brightness and enhanced contrast to give the optimum solution.

Coupled with DT's interface solutions (RGB, video, and DVI), single board computer (SBC), and touchscreen options customers can source exactly the solutions they need.

There is a huge replacement market for plasma screens that have suffered from image burn-in, unreliable fans and heat dissipation issues, whereas TFTs offer higher resolution, lower power, reduced weight, no burn-in, as well as excellent viewing angles, higher brightness and contrast.

Although still more expensive than plasma, many companies have now calculated that the TFT LCD still offers a lower-cost long-term option than plasma. TFTs have a 5 year plus lifetime expectancy plus replaceable backlights possible whereas plasma needs often to be replaced after only around 2 years. The lifetime costs are in fact lower for TFT than plasma, plus they offer many advantages. TFTs are ready to oust plasma eventually to a relatively niche application product.

2.4 Give English equivalents.

Вбудована пам’ять, частота оновлення, щоб компенсувати цей недолік, за рахунок, порівнянно з, задовольняти потреби, кольоровий монітор, перетин рядів і стовпців, завдяки досягненням, повне зображення, накладатися один на один, викривлювати, бажаний колір, сумісний, включати в систему плату, розташовувати рядками і стовпцями.

2.5 Translate into English the following sentences using the… the… (with two comparatives) to say that one thing depends on another thing. Find the sentences with such a structure in the text.

1. Чим більше пікселів на екрані, тим краща якість зображення.

2. Чим менше розмір екрану, тим чіткіше зображення.

3. Чим вища роздільна здатність, тим більша вартість дисплея.

2.6 Translate the following sentences into English.

1. Кількість точок по горизонталі та вертикалі, які монітор здатний відтворити чітко й роздільно, називається його роздільною здатністю.

2. Важливою характеристикою монітора є частота оновлення зображення

3. Кращі моделі моніторів забезпечують частоту оновлення до 200 Гц

4. Чим вища частота оновлення, тим менше буде помітно мерехтіння і менше будуть втомлюватися очі під час роботи з монітором.

5. Розмір точки – це відстань по вертикалі між центрами сусідніх точок на екрані монітора у мм.

7.Рідкі кристали можуть змінювати свою молекулярну структуру, що дозволяє з допомогою електричних сигналів управляти світловим потоком, який проходить через них.

2.7 Fill in the blanks with the words from the text.

1. The total number of pixels displayed across and down on the display screen is known as ___________.

2. _____________ of the monitor is very similar to that of a TV set.

3. The monitor is controlled by a separate circuit board known as the ___________.

4. Portable computers use a flat _____________.

5. Three separate electron beams represent the three primary colours: ____________.

2.8 Read the passage and compare passive matrix and active-matrix LCDs.

Passive-matrix LCDs use a simple grid to supply the charge to a particular pixel on the display. Creating the grid is quite a process! It starts with two glass layers called substrates. One substrate is given columns and the other is given rows made from a transparent conductive material. This is usually indium-tin oxide. The rows or columns are connected to integrated circuits that control when a charge is sent down a particular column or row. The liquid crystal material is sandwiched between the two glass substrates, and a polarizing film is added to the outer side of each substrate. To turn on a pixel, the integrated circuit sends a charge down the correct column of one substrate and a ground activated on the correct row of the other. The row and column intersect at the designated pixel, and that delivers the voltage to untwist the liquid crystals at that pixel.

The simplicity of the passive-matrix system is beautiful, but it has significant drawbacks, notably slow response time and imprecise voltage control. Response time refers to the LCD's ability to refresh the image displayed. The easiest way to observe slow response time in a passive-matrix LCD is to move the mouse pointer quickly from one side of the screen to the other. You will notice a series of "ghosts" following the pointer. Imprecise voltage control hinders the passive matrix's ability to influence only one pixel at a time. When voltage is applied to untwist one pixel, the pixels around it also partially untwist, which makes images appear fuzzy and lacking in contrast.

2.9 Put the verb into the correct form.

1. What is the importance of pixel resolution?

2. What unit of frequency is used to measure the refresh rate of a monitor?

3. What is the most common display?

4. What are the advantages and disadvantages of LCD and CRT displays?

5. What is the main drawback of LCDs? What are the ways of its elimination?

6. In what way is the problem of aliasing solved?

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