Video 1 > Display and Projection Technologies > Flashcards
Display and Projection Technologies Flashcards
Three Methods of Displaying Images
Transmissive
Reflective
Emissive
Transmissive
Light is transmitted through a screen
Reflective
Light bouncing off a screen and reflecting to our eyes
Emissive
Light is created by the display and sent outward
Rear Screen Projection (5)
- transmissive
- good contrast ratio
- possibility of large displays
- require more space
- can lead to hot spotting
Front Screen Projection (5)
- reflective
- the possibility of large displays
- flexible options.
- lower contrast ratio
- potential for fan and projector noise
plasma display (3)
- emissive technology
- fixed resolution
- Pixels comprised on RGB phosphors
LCD (3)
- Transmissive
- Liquid crystals
- Fixed resolution
LCD projectors
use light from the projection lamp and refract it into three colors by special dichroic mirrors
Panels of LEDs (4)
- used to create full images
- Red, green and blue LEDs are grouped together to form pixels
- the pixels are grouped together in a module
- Modules are put together to form a larger image
DLP (3)
- Reflective
- Digital Light Processing
- Fixed resolution
OLED Technology (3)
- Emissive
- Chemical compounds emit light
- Emerging technology
LED (3)
- Emissive
- Light emitting diodes
- Fixed resolution
Laser (3)
- Reflective
- 3 lasers produce image
- Requires use of MEMS (Micro ElectroMechanical System)
Interactive Whiteboard (3)
- Reflective/ Emissive
- Often incorporate an integrated short-throw projector
- Stylus, touch, and multi-touch
Touchscreen (3)
- Emissive
- Human-to-machine control device for user
- Interact with fingers or stylus
Augmented Reality (3)
- Emissive
- Real-world environment altered by computer-generated graphics or information
- Also called mixed reality or computer-mediated reality
Virtual Reality (3)
- Emissive
- Computer-generated environment that user experiences through headset or projected system
- System can use haptic technology to recreate sensations of touch and feel
Plasma Technology
also called plasma displays, are fixed resolution emissive imaging devices. Plasma displays combine phosphors in pixels and are available as both fully integrated televisions or as monitors. They have wide viewing angles, high contrast, excellent color saturation, low black levels, and offer very good picture quality under normal room lighting conditions.
Plasmas contain hundreds of thousands of tiny pixels. In the photo below, each pixel is made up of three cells, or subpixels, consisting of red, green, and blue phosphors. Each pixel is filled with neon and xenon gas. When a high voltage is discharged through a pixel, the gas inside ionizes and gives off ultraviolet rays. These rays strike the phosphors, causing them to glow.
Because plasma pixels can only operate in a switched on/off mode, they are digital display systems, even though the phosphor response to the discharged voltage is analog.
Plasma monitors can handle a wide variety of computer and video signals. However, plasma monitors have a fixed-resolution pixel matrix and therefore must scale images up or down to match their native resolution.
While some legacy plasma displays may still be in operation, the manufacturing of them has been phased out.
LCD Technology
(LCDs) use a grid of pixels to create images on a screen. Each pixel on the screen is filled with a liquid crystal compound. LCD is another example of a fixed resolution display technology. The pixel resolution is usually based on computer display standards. The pixel resolution is known as the native resolution.
To create an image in an LCD display, light must first pass through a polarizer
A polarizer is a set of extremely fine parallel lines that act like a net, or filter. They block all light waves that are not parallel to those lines.
The polarized light then travels through a sandwich of transparent switching transistors and liquid crystals. LCD displays utilize two sheets of polarizing material. The liquid crystal solution is sealed between them. When a transistor is turned on, a specific voltage is applied to its pixel. The tiny liquid crystals within each pixel act like light shutters, passing or blocking varying amounts of light.
Each transistor has to be shielded from the light that goes through the LCD, so it is covered with a non-transparent chemical layer called the black matrix. The black matrix also creates a defined edge around every pixel, causing a visible “screen door” effect on lower resolution displays. The ratio between the remaining transmissive surface of each pixel and the total surface of the LCD is called the aperture ratio. The smaller the transistors are compared to the size of the pixel, the higher the aperture ratio and the more light that will pass through. Higher aperture ratios result in fewer image artifacts, such as the previously mentioned “screen door” effect.
A color LCD display has three filters in each imaging pixel array - one for each primary color: red, green, and blue. The backlight can be compact fluorescent tubes or light-emitting diodes
LED Technology
An LED is a semiconductor, like a transistor. It has no moving parts. It glows when the correct low voltage is applied to its contacts.
We see LEDs all the time as indicator lights on electronics. They are generally plastic, and commonly come in white, red, green, yellow, and blue.
LEDs are used in several different technologies: panels or walls, projection systems, and backlights to illuminate LCD panels. LEDs are efficient and have a long life, which makes them a good alternative to other technologies.
Panels of LEDs are used to create full images. As you know, in order to make white light, we require red, green, and blue light. Red, green and blue LEDs are grouped together to form pixels. Typically, the pixels are grouped together in a module. Modules are put together to form a larger image, not unlike the pieces of a puzzle.
LED walls are used for indoor and outdoor advertising. They are used in sporting arenas and have been installed on moving vehicles as well. LED walls are able to show an image even in bright sunlight.
LEDs are replacing traditional lamps in projection systems. Because of the longer life of LEDs over traditional lamps, lamp replacement, in many cases, will not be necessary. Increasingly laser, or hybrid LED/laser, light source technologies are being used in favor of traditional lamps.
Fluorescent Cathode Tubes are used to backlight LCD panels. Now, they are being replaced by LEDs. LEDs are less expensive, produce an even light, and have a long life. Due to the LEDs small size, thinner displays can be manufactured.
OLED Technology
Organic Light-Emitting Display (OLED) technology is based on layers of organic, carbon-based, chemical compounds that emit light when an electric current flows through the device. There are separate organic layers for red, green, and blue.
OLEDs are emissive devices, meaning they create their own light, as opposed to LCDs, which require a separate light source. As a result, OLED devices use less power, but they are capable of higher brightness and fuller color than LCDs.
OLEDs are imprinted on a very thin silicon substrate. The active matrix silicon-integrated circuits are imprinted directly under the display, controlling the power to each organic point of light diode (pixel), performing certain image control functions at a very high speed. OLEDs’ capability to refresh in microseconds rather than milliseconds, as LCD displays do, creates highly dynamic motion video.
When a voltage is applied to the cathode (1) and anode (5), a combining of electrons and protons occurs near the emission layer (2). This creates a radiation of energy (3) in the visual frequency range.
The color (frequency) of the light radiated is determined by the type of materials used for the emissive (2) and conductive layers (4). Stacking Red, Blue and Green OLEDs allows for a much higher resolution than current LED or pixel based technologies that require one of each placed next to each other.
OLED devices have a relatively short lifespan because the brightness of the organic material decreases with time. The red and green materials last at least 20,000 hours, while the blue materials burn out before that.
This technology is readily available for different applications – the AV industry is constantly changing and growing as new technologies mature.
DLP Technology
was developed by Texas Instruments. DLP projectors reflect light to create images, and are fixed-resolution displays.
Close up image of a micro-mirror device
At the heart of a DLP projector is a specialized integrated circuit known as a Digital Micromirror Device (DMD). DMDs are available in resolutions from 800x600 pixels (SVGA) to over 2 million pixels (2K, or 2048x1080 for digital cinema). The individual mirrors tilt back and forth over a 12-degree arc to reflect or block light, and are very small, only microns in size.
If you have ever been to a football (soccer) match, you might have seen one section of fans hold up and tilt large cards to form pictures or words. Change those cards to mirrors, and you have a very large digital micromirror device.
Each mirror in a DMD is a pixel. Digital signals tell each mirror to tilt back and forth rapidly between two tiny posts, on and off. When a mirror is tilted on, light reflects through the projection lens. When the mirror is tilted off, the light is reflected to a light absorber.
Because DMDs only have two states – on and off – they must use pulse-width modulation (PWM) to create shades of gray in images. In a PWM system, the ratio of “on” cycles to “off” cycles within a specific time interval creates a luminance value. The on-off cycle is so fast in a DMD that our eyes don’t see any flicker at all.
Color is added in one of two ways. A single-chip DLP projector uses a high-speed color wheel that is precisely synchronized to the motion of the mirrors. Red, green, and blue information (and sometimes white) is presented in sequence to our eyes, which see this information as real-time color imaging. This process is also known as scanning color. It can create a small rainbow artifact when bright white lines or text are shown and our eyes blink or move across the image. This effect is not unlike that produced by a stroboscope.
Larger DLP projectors use three discrete DMDs and split white light from a projection lamp into red, green, and blue light. The monochromatic images from the three DMDs are then combined in precise registration using a polarizing beam splitter (PBM). There are no flickers or rainbow artifacts with 3-chip DLP projectors.
Laser Technology
Laser projection uses three lasers – red, green, and blue – to produce images on a screen.
The intensity of each laser is determined by the incoming video signal. The lasers’ light output is sent to an optical combiner that outputs a single beam of light. This light beam reflects off a MicroElectroMechanical Systems (MEMS) mirror, which scans that beam across the screen.
Lasers are used in broad range of applications, from very small to very large.
On the small end, lasers are sometimes used in pico-projectors. This is the technology used in pocket-sized devices such as mobile phones. On the large end, lasers are used for very large screens, like displaying images on buildings and large theaters.
Laser projection is also becoming more commonplace in standard corporate or education meeting spaces.
Electronic Whiteboards
Conventional chalkboards have long been a tool for conveying ideas to a group. The common classroom had numerous "blackboards" on which math problems could be worked, or language studies could be written down using chalk. The dry-erase white board has replaced many blackboards because of their ease of use. These whiteboards are practically dust free and multi-colored writing pens make communication more colorful and detailed. Today, there are interactive whiteboards connected to a computer and projector. Each pen stroke can be recorded for later playback, and entire documents can be stored as a single image. A university professor may explain a physics lesson on the electronic whiteboard to the class. After class, the student may wish to review the materials presented on the board. The student simply logs onto the university website, gets the file for the class whiteboard and replays it in his or her room, reliving the classroom experience. Electronic interactive whiteboards can operate on several different principles. Lasers may scan the surface of the board looking for any pen / eraser movement. The device may be pressure sensitive, detecting where a pen (or finger) is touching the surface and recording that as a pen stroke. In either case, the data is logged for display or archived for future use.
Touchscreen Technology
Touchscreens allow you to control a computer, device or control system by simply touching the screen itself. In the AV industry, touchscreens are generally used with display devices. The display shows an image and the touchscreen is overlaid and used to control the image or used as input for a computer program.
A touchscreen is used much like a mouse. However, a mouse only has one “pointer,” or area of control. Touchscreens can have one, two, or more points of control, allowing you to pinch or pull images around a screen.
There are a number of technologies used in touchscreens, too many to mention in this course. Some technologies only work with a certain type of touch and will not work with others. One technology might need a change of capacitance that only a human finger can provide, while another needs a sharp tap of a stylus. Always compare your method of touch and the touch technology for your system.
Augmented Reality
Augmented reality is an emerging, emissive technology in which the real-world environment is altered by computer-generated graphics or information.
This technology can also be called mixed reality or computer-mediated reality.
Virtual Reality
Virtual reality is an emerging, emissive technology in which there is a wholly computer-generated environment that the user experiences as reality through a headset or a projected system.
This technology can also include haptic technology to recreate sensations of touch and feel.
