Digital television systems (DTS) Projectors and displays Technical Univ. of Kosice Faculty of Electrical Engineering and Informatics Lˇ. Maceková, 2017

A projector or image projector is an optical device that projects an image (or moving images) onto a surface, commonly a projection screen. Most projectors create an image by shining a light through a small transparent lens, but some newer types of projectors can project the image directly, by using lasers. A virtual retinal display, or retinal projector, is a projector that projects an image directly on the retina instead of using an external projection screen. The newest types of projectors are handheld projectors that use lasers or LEDs to project images. Their projections are hard to see if there is too much ambient light. [Wikipedia]

A projector is an instrument used top produce a large image of a small object. The slide, or film, is placed behind the projector lens outside its focal length and is illuminated but a small but powerful source of light.  The amount of light from the source actually going through the transparent slide or film is increased by using a condenser and a concave mirror. The slide must be put into the projector upside down to give an image on the screen which is the right way up. [http://www.schoolphysics.co.uk/age11-14/Light/text/Projector/index.html]

Projection TVs are a cross between the two technologies: they use television technology to build up a picture and projector technology to throw that picture onto the screen. huge, old-style cathode-ray tube (CRT) TV sets have gradually given way to flatter, squarer LCD (liquid-crystal display) and plasma TVs that work an entirely different way. Projection TVs have evolved in much the same way. - basic CRT TV projectors were available in the 1950s, - in the 1980s thanks to manufacturers such as Barco, they use three hugely powerful light guns to shine separate red, blue, and green images onto a screen (through front projection). The images fuse together into a single, large colored image. The trouble with projectors like this is that they are huge and heavy (so they're not easily portable), they can use lots of electricity (to power the three light guns), and the CRT tubes inside them get very hot. But although they can be fiddly to set up initially and adjust, they're neither unreliable nor obsolete, as many people suppose: they give excellent picture quality (as good as or better than newer technologies) and they're still compatible with new developments like HDTV and Blu-ray DVD players.

LCD screens are smaller, lighter, cheaper, more reliable, and use much less power than CRTs. In an LCD TV projector, a very bright light shines through a small LCD screen into a lens, which throws a hugely magnified image of the screen onto the wall. The technology is sometimes called LCLV (liquid crystal light valve). The image quality is often poorer than that produced by CRT projectors and the bright lamps used inside LCD projectors to throw the image still have a limited life. http://www.explainthatstuff.com/projectiontv.html

DLP - projectors DLP® (digital light processing), uses an entirely different method of making images using microscopic mirrors. Developed in 1987 by Texas Instruments scientist Dr Larry J. Hornbeck, - microchip called a digital micromirror device (DMD) - contains about two million tiny mirrors arranged in a square grid. Each mirror is less than one fifth the diameter of a human hair, and it's mounted on a microscopic hinge so it can tilt either one way or another. A bright lamp shines onto the DMD mirror chip and an electronic circuit makes the mirrors tilt back and forth. If a mirror tilts toward the lamp, it catches the light and reflects it off toward the screen, creating a single bright dot of light (equivalent to a pixel of light made by a normal TV); if a mirror tilts away from the light source, it can't catch any light, so it makes a dark pixel on the screen instead. Each mirror is separately controlled by an electronic switch so, working together, the two million mirrors can build up a high-resolution image from two million light or dark dots. To make color images, DLP projectors need an extra bit of technology: they have a spinning colored wheel inserted into the light path, which can color the pixels red, blue, or green. Combined with the tilting mirrors, the color wheel makes a front-projected TV picture from millions of pixels of every possible color.

2D projection 3D (2D ?) projection is any method of mapping three-dimensional points to a two-dimensional plane. As most current methods for displaying graphical data are based on planar (pixel information from several bitplanes) two-dimensional media, the use of this type of projection is widespread, especially in computer graphics, engineering and drafting [Wikipedia]. Orthographic projection When the human eye looks at a scene, objects in the distance appear smaller than objects close by. Orthographic projection ignores this effect to allow the creation of to-scale drawings for construction and engineering. It is a form of parallel projection, in which all the projection lines are orthogonal to the projection plane. Weak perspective projection - uses the same principles of an orthographic projection, but requires the scaling factor to be specified, thus ensuring that closer objects appear bigger in the projection, and vice versa. It can be seen as a hybrid between an orthographic and a perspective projection, and described either as a perspective projection with individual point depths  Zi replaced by an average constant depth Zave or simply as an orthographic projection plus a scaling.

3D - projection Perspective projection When the human eye views a scene, objects in the distance appear smaller than objects close by - this is known as perspective. While orthographic projection ignores this effect to allow accurate measurements, perspective projection shows distant objects as smaller to provide additional realism. 3D - projection

3D Display A stereo display (also 3D display) is a display device capable of conveying depth perception to the viewer by means of stereopsis for binocular vision. The basic technique of stereo displays is to present offset images that are displayed separately to the left and right eye. Both of these 2D offset images are then combined in the brain to give the perception of 3D depth

3D television   - is television that conveys depth perception to the viewer by employing techniques such as stereoscopic display, multi-view display, 2D-plus-depth, or any other form of 3D display. Most modern 3D television sets use an active shutter 3D system or a polarized 3D system, and some are autostereoscopic without the need of glasses. 3D TV are to be discontinued in 2017 due to low consumer demand. LG and Sony were the last manufacturers to build the product.[1] However, only limited 4K TVs with 3D capability still exist.

TV Displays

CRT – Cathode Ray Tube For the past 75 years, the vast majority of televisions have been built around the same technology: the cathode ray tube (CRT). In a CRT television, a gun fires a beam of electrons (negatively-charged particles generated by cathode) inside a large glass tube. The electrons excite phosphor atoms along the wide end of the tube (the screen, the anode), which causes the phosphor atoms to light up. The television image is produced by lighting up different areas of the phosphor coating with different colors at different intensities. Cathode ray tubes produce crisp, vibrant images, but they do have a serious drawback: They are bulky. In order to increase the screen width in a CRT set, you also have to increase the length of the tube (to give the scanning electron gun room to reach all parts of the screen). Consequently, any big-screen CRT television is going to weigh a ton and take up a sizable chunk of a room. [https://electronics.howstuffworks.com/plasma-display.htm] Fig. Cathode Ray Tube [https://www.elprocus.com/cathode-ray-tube/]

LCD displays A liquid-crystal display (LCD) is a flat-panel display or other electronically modulated optical device that uses the light-modulating properties of liquid crystals. Liquid crystals do not emit light directly, instead using a backlight or reflector to produce images in colour or monochrome [Wikipedia]. The principle behind the LCD’s is that when an electrical current is applied to the liquid crystal molecule, the molecule tends to untwist. This causes the angle of light which is passing through the molecule of the polarized glass and also cause a change in the angle of the top polarizing filter. As a result a little light is allowed to pass the polarized glass through a particular area of the LCD. Thus that particular area will become dark compared to other. The LCD works on the principle of blocking light. While constructing the LCD’s, a reflected mirror is arranged at the back. An electrode plane is made of indium-tin oxide which is kept on top and a polarized glass with a polarizing film is also added on the bottom of the device. The complete region of the LCD has to be enclosed by a common electrode and above it should be the liquid crystal matter. [https://www.elprocus.com/ever-wondered-lcd-works/] An LCD is made with either a passive matrix or an active matrix display display grid. The active matrix LCD is also known as a thin film transistor (TFT) display. The passive matrix LCD has a grid of conductors with pixels located at each intersection in the grid. A current is sent across two conductors on the grid to control the light for any pixel.

LCD displays 1. The basic structure of LCD should be controlled by changing the applied current. 2. We must use a polarized light. 3. Liquid crystal should be able to control both of the operation to transmit or can also to change the polarized light. https://www.elprocus.com/ever-wondered-lcd-works/

LED displays The LED TV is a more advanced version of the LCD TV. While both types of TV rely on LCD technology and have flat-panel designs, the online review resource, TopTenReviews notes, "LED TVs are slimmer, brighter, and more detailed than your traditional LCD TV." LED TVs function by illuminating LCD panels with LED backlighting. However, not all LED TVs utilize the same type of LED backlighting [http://smallbusiness.chron.com/led-tv-work-26798.html]. An LED TV illuminates its LCD panel with light-emitting diodes. LEDs consist of small semiconductors, which glow during exposure to electric current. Specifically, this current flows between LED anodes, which are positively charged electrodes, and LED cathodes, which are negatively charged electrodes. In contrast, a traditional LCD TV utilizes fluorescent lamps for backlighting. These lamps function by using mercury vapory to create ultraviolet rays, which in turn cause the phosphor coating of the lamps to glow. LEDs have several advantages over fluorescent lamps, including requiring less energy and being able to produce brighter on-screen colors (visible also in outdoors.

LED displays Fig. Detail view of a LED display with a matrix of red, green and blue diodes [Wikipedia]

OLED Organic light-emitting diode – display [Wikipedia] OLED is a light-emitting diode (LED) in which the emissiveelectroluminescent layer is a film of organic compound that emits light in response to an electric current. This layer of organic semiconductor is situated between two electrodes; typically, at least one of these electrodes is transparent. OLEDs are used to create digital displays in devices such as television screens, computer monitors, portable systems such as mobile phones, handheld game consoles and PDAs. A major area of research is the development of white OLED devices for use in solid-state lighting applications. An OLED display works without a backlight; thus, it can display deep black levels and can be thinner and lighter than a liquid crystal display (LCD). In low ambient light conditions (such as a dark room), an OLED screen can achieve a higher contrast ratio than an LCD, regardless of whether the LCD uses cold cathode fluorescent lamps or an LED backlight. Fig. Schematic of a bilayer OLED: 1. Cathode (−), 2. Emissive Layer, 3. Emission of radiation, 4. Conductive Layer, 5. Anode (+)

OLED Fig. OLED illustration

PLASMA A plasma display panel (PDP) is a type of flat panel display common to large TV displays 30 inches (76 cm) or larger. They are called "plasma" displays because they use small cells containing electrically charged ionized gases, which are plasmas. Plasma displays have lost nearly all market share, mostly due to competition from low-cost LCD and more expensive but high-contrast OLED flat-panel displays; manufacturing for the United States retail market ended in 2014, and manufacturing for the Chinese market was expected to end in 2016. [Wikipedia] solid ⇒ liquid ⇒ gas⇒ plasma Fig.: Each pixel on the screen is illuminated by a tiny bit of plasma or charged gas, somewhat like a tiny neon light. 

TFT LCD display A thin-film-transistor liquid-crystal display is a variant of a liquid-crystal display (LCD) that uses thin-film transistor (TFT) technology to improve image qualities such as addressability and contrast.  TFT LCD panel contains a specific number of unit pixels often called subpixels.  Each unit pixel has a TFT, a pixel electrode (IT0), and a storage capacitor (Cs). Because each unit pixel is connected through the matrix, each is individually addressable from the bonding pads at the ends of the rows and columns.  [http://www.proculustech.com/detail/203/408.html , Wikipedia]

TFT LCD display The similar TFT technologies: 1.Twisted nematic (TN) 2.In-Plane Switching (IPS) / Hitachi 3.Patterned vertical alignment (PVA). /Sony 4.Advanced super view (ASV)./Sharp 5.Plane Line Switching (PLS) / Samsung. Fig.: A diagram of pixel layout

Much more technologies are in development... [Wikipedia]