Visual Display Unit (Monitors)

All computers are connected to some type of display unit, which is called a monitor. The monitor is a part of the computer video system and monitors are available in many different types and size. The on-screen display enables us to see how applications are processing our data, but Visual display unit is important to remember that the screen display is not permanent record i.e. the outputs are lost where the power is off. The thinner monitors used on notebook and other small computer are known as flat-panel displays. Compared to CRT (Cathode Ray Tube) based monitors, flat panel displays consume less electricity and take up much less room.

Visual Display Unit (Monitors) 1

Most flat panel displays use Liquid Crystal Display (LCD) technology. LCD displays sandwich cells containing tiny crystals between two transparent surfaces. By varying the electrical current supplied to each crystal, an images forms. Quality of monitor is often judged in terms of following four factors:

None The most important aspect of a monitor is its size. Like televisions, screen sizes are measured in diagonal inches, the distance from lower left corner to the upper right corner diagonally.

Typical monitors found in the market are of size 14 inches, and 17 inches and above. The size of display are determines monitor quality. In larger monitors the objects look bigger or more objects can be fitted on the screen.

None The screen image is composed of a number of pixel elements. A team pixel is the smallest unit of display screen (the word comes from combination of picture and elements). Each pixel is composed of three phosphor dots, Red, Green and Blue. Now the Dot- pitch is the distance between the phosphor dots that make up a single pixel.

The Dot-pitch of color monitors for PCs ranges from about 0.15 mm to 0.30 mm.

None resolution. The resolution of a monitor indicates how densely the pixels (a single point in a graphic image) are packed. On color monitors, each pixel is actually composed of three dots - a Red, Green and Blue. Ideally the three points should converge at the same point. Resolution indicates the quality of monitor.

Greater the number of pixels, better the resolution and sharper the image. Actually the resolution is determined by the video controller or video adapter card. IBM has provided following adapter cards: The maximum under of points that can be displayed without overlap on a monitor screen is referred to as the. The resolution of a monitor indicates how densely the pixels (a single point in a graphic image) are packed. On color monitors, each pixel is actually composed of three dots - a Red, Green and Blue.

Visual Display Unit (Monitors) 2

Ideally the three points should converge at the same point. Resolution indicates the quality of monitor. Greater the number of pixels, better the resolution and sharper the image. Actually the resolution is determined by the video controller or video adapter card. IBM has provided following adapter cards:


Refresh Rate: Refresh Rate is the number of times per second at which each pixel on a screen is refreshed. Display monitors must be redrawn many times per second. The refresh rate for a monitor is measured in hertz (HZ) or cycles/second. Generally monitors refresh rates are 60 HZ or 70 HZ. The faster the refresh rate the less the monitor flickers. Monitors are classified into three categories according to its display color

Monochrome: Monochrome monitors actually display two colors, one for the background and another for foreground.

The color can be black (background) and white (foreground), black (background) and green (foreground).

Grey-scale: Gray-scale is a special type of monochrome monitor capable of displaying different shades of gray. Background color is usually white in such monitors. Color: Color monitors can display from 1 to 16 million different colours. These monitors are sometimes called RGB (Red, Green, and Blue) monitors because three primary colors Red, Green and Blue are used to make other colours. An RGB monitor consists of cathode ray tube with three-electron guns-one each for Red, Green and Blue at one end and screen at the other end.

Color and gray-scale monitors are often classified by the number of they use to represent each pixel. For example, a 14-bit monitor represents each pixel with 24 bits. The more bits per pixel, the more colors and shades the monitor can display. A traditional picture tube is like a big glass bottle. There are electron guns in the narrow end.

They fire towards the large flat surface facing the user. The inside of the glass surface is coated with tiny phosphorus dots. There are arrange in groups of three- Red, Blue and Green (for color monitor) phosphorus dot. These dots light up or grow when hit by electrons from the electron gun. The more powerful beam is, the brighter they get. The electron beams are guided by electromagnets, where bend the beams, so they hit the exact desired phosphorus dot.

Data imaged is product by moving the electron beam across the phosphor coated screen. Phosphor coating can be made to glow with different intensities by varying the strength of the electron beam, which finally forms character on screen. CRT monitor contains a shadow mask, which is fine mesh made of up metal., fitted to the shape and size of the screen. The holes in the shadow mask's mesh are used to align the electron beams, to insure that they strike precisely the correct phosphorus dot. Mostly, these holes are arranged in triangles.

CRT monitor are popular with desktop computers. These are available in monochrome and color monitors. The CRT has display screen of 25 lines of 80 characters each. There are two types of CRT monitors:

Composite CRT monitor is used only one electron gun to control the intensity of all these phosphorus dots in each pixel. RGB CRT monitor uses three individual guns, one for its dot, to control the intensity.

Each of the sub dots are hit by its own electron gun that is why these monitors give sharper picture.

a) As the phosphor dots start to fade after sometime they are hit by the electron gun, they need to be refreshed again.

c) They are bulky and heavy. A CRT screen is reliable but it is bulky & consumes a lot of power so it is not used for portable computers. For small computers, flat panel display is used. The most common type of flat panel display are:

LCD produces images by aligning molecular crystals. When a voltage is applied, the crystals line up in a way that blocks light from passing through them and the absence of light is seen as characters on the screen.

The LCD screen is flat, since it does not have picture tube. Instead the screen image is generated on a flat plastic disk. Thus LCD screens are much thinner, soft and do not flicker as compared to CRT.

None LCD is light weight, flat, thin and require less space.

None LCD have smaller viewing angle so picture is best viewed when the person is in straight position from the centre of monitor.

None The liquid crystals do not emit light so the images are less sharp.

None There is a need of backlight setting to enhance sharpness of images. One of the advancement in flat panel display is GPD. Gas Plasma diplay offers flicker free viewing and has higher contrast than LCDs. GPD contains ionized gas (Neon or Xenon) in between two glass plates. Among the two glass plates, one has serial of vertical wires or electrodes while other has series of horizontal wires.

When the two placed together, the intersection of horizontal and vertical wire identifies a pixel. When current is applied through appropriate vertical and horizontal lines, the gas at the pixel emits light. Thus characters are formed by glowing combination of appropriate pixels.

Given current technology, could TV display screens double as video camera sensors?

Even IF - Why would you want to take a photo with zero (or near few mm) field of vision and a lot of blur? Because TV screen would (could) act like a photosensitive paper (or if you are old enough camera film). There would be no lens to focus, no apertures to set the amount of light, no pinholes that would allow you to point to certain area. Screen would take light from everywhere that is not behind the TV. And what would be behind the TV would (could) still have ambient light. So a photo taken with such screen would be very bright (white) on border going to greyish in the middle. Just put a normal camera in the TV. Speakers can work as microphones anyway.

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Samsung Has Developed Ultra-thin Interactive Holographic Display Screen, and the Era of Holographic
At the 2020 world artificial intelligence conference held on July 9 this year, Ma Yun and musk were "on the same stage" again.Affected by the epidemic situation that day, waic adopted the cloud form for the first time in its history. As the final speaker of the opening ceremony of the conference, Ma Yun was in Yunnan. A technology connected him with us - holographic projection.In fact, this technology has a history of more than 70 years.As early as 1947, the British Hungarian physicist g bor D NES invented holographic projection. Based on this achievement, he won the young's prize of the British Physical Society in 1967 and the Nobel Prize in physics in 1971.Recently, Samsung, known as the "display overlord", has made a new breakthrough in this field - proposed an ultra-thin interactive holographic display, which can provide high-resolution and highly realistic 3D video from multiple angles. In the future, it can be integrated into mobile devices to support office or home.What is holography?The scientific research team to achieve this breakthrough comes from Samsung Institute of advanced technology (sait), the optical research group of sait Russia and Seoul University.On November 10, 2020, his paper was published in nature communication, a subsidiary of nature, entitled slim panel holography video display.Before understanding this paper, what is holography is the first problem to understand.Holographic projection is essentially a 3D technology. Its English name is holographic projection, in which holo comes from Greek, meaning "complete information".To deliver a "complete message", you need two steps:Shooting: using the interference principle (that is, when two or more columns of waves overlap in space, they will be superimposed to form a new waveform), the object beam formed by the subject under laser irradiation and the laser reference beam emitted on the holographic negative will be superimposed to generate interference and recorded. After certain processing, the hologram is obtained.Imaging: Based on the diffraction principle (i.e. the wave will deviate from the original linear propagation when encountering obstacles), the hologram is illuminated by coherent laser. The diffracted light wave of a linearly recorded sinusoidal hologram can give two images, which enhances the three-dimensional sense of the image and has a real visual effect.In short, the principle of holographic projection technology can be understood as: skillfully take an object into a photo by using two physical phenomena, and then create a three-dimensional feeling.For this reason, holographic projection is also called virtual imaging.It is worth mentioning that when real objects and holograms are in the same space, they can be perceived without difference.For example, in the following photo, a real hand holds a holographic display screen, on which is the image of an elf. Both the hologram and the hand are 0.3 meters away from the camera that took the picture.Holographic display provides natural depth perception, and the audience pays more attention to the spirit itself than the screen.In contrast, if it is a traditional three-dimensional 3D image using binocular parallax and convergence (i.e. convergence of eyes when looking at near objects), the audience may not be able to clearly see the elf image and hand at the same time, and there will be visual fatigue caused by reconciliation convergence conflict.Therefore, holographic display can be said to be an important part of the future video system.In fact, since its discovery in 1947, holographic technology has become a classic element in science fiction films, and people's cognition of it has always been that it can reproduce the most real 3D images without visual discomfort.The viewing angle is expanded by 30 times, and 4K high-resolution holograms are generated in real timeIn 1990, the MIT Media Lab developed the first holographic video system. Since then, the commercialization of holographic video has become a major research direction in this field.In May 2018, American camera giant red launched the world's first commercial holographic projection smartphone hydrogenone.At that time, although this mobile phone attracted great attention from the outside world, when the product was launched, people in the industry and the media said that this mobile phone failed to give a satisfactory user experience in holographic projection. In fact, until today, there is still a bottleneck in the realization of "commercial holographic video display".Samsung Seoul University team said in the paper: commercial holographic video displays have not been introduced in batches, mainly due to narrow viewing angle, bulky optical equipment and high requirements for computing power.Specifically, to build a mobile holographic video display suitable for commercialization, three obstacles need to be overcome:1. The limitation of space bandwidth product (SBP), which determines the size and viewing angle of holographic image.2. In order to produce large coherent background light, complex optical elements and considerable space are needed to process light. Therefore, it is not easy to realize a holographic video display as thin as a tablet.3. Real time holograms usually require a lot of calculation, and the amount of calculation will increase with the increase of spatial bandwidth product.Based on the above problems, the ultra-thin interactive holographic display proposed by Samsung & Seoul University team has two special designs:One is the steering backlight unit composed of coherent Blu (c-blu) and beam deflector (BD). On the one hand, it expands the effective spatial bandwidth product (i.e. viewing angle) by 30 times, thus realizing the dynamic hologram with the largest viewing angle in history; On the other hand, its diffractive waveguide architecture ensures the final ultra-thin design of the display screen, with a total thickness of no more than 10 cm.The two blue arrows in the following figure are the expanded visual range.The second is a holographic video processor including data propagation unit (DPU), filter and scaling unit (FSU) and 32 fast inverse Fourier transform processors. A single chip can generate 4K high-resolution holograms in real time.Finally, the prototype of holographic video display screen is shown in the figure below. The marks in the figure below are: spatial light modulator, geometric phase lens, coherent backlight unit, beam deflector and holographic video processor from top to bottom.Moreover, the system bus used by Samsung Seoul University team is ambaaxi4, which is widely used in smartphone application processor. Therefore, embedding holographic video processor into smartphone application processor can also be realized in the future.Finally, let's feel a 4K turtle swimming map projected by this holographic display screen that supports multi angle viewing. The direction the turtle swims can be controlled by pressing the key directly.It seems ordinary, but in fact, due to the different depth of all objects in the picture, the definition of holographic objects will change with the focus of the camera.The following figure is a video screenshot. In the illustration at the upper right corner of figure a, coral is clearer than tortoise; In the illustration of figure B, turtles are clearer than corals.This is the same as whether our camera focuses or not. Naturally, it also reflects the uniqueness of holograms - they can provide debugging, and the final image is no different from the real object.So far, holographic projection, a magical technology with a history of more than 70 years, has made an important breakthrough. We are not far from holographic projection on mobile phones. Editor ajx
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