Many different tools are used for displaying a multimedia system. Multimedia systems depend on both hardware and software to create and display different types of media.
Students Learn About: displaying in multimedia systems
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Watch these videos as a Pre Class learning exercise:
Screens
CRT and LCD.mp4
A screen is a display surface that provides immediate feedback about what the computer is doing. It can display text, image, animation and video data. The most common type of screen is a monitor. It uses CRT (cathode ray tube) technology.
CRT displays produce images by firing a stream of electrons onto the inside of the screen, which is coated with tiny dots or pixels made of phosphor.Monochrome monitors use one stream, and colour monitors use three streams to strike red, green and blue phosphor. When the stream of electrons hits the pixel, the phosphor glows to produce the image. The process by which the colour of a pixel changes gradually from its original colour to a new colour is called a cross fade. The total intensity of the pixel usually remains constant during this process.
Most CRT displays use a raster scan. A raster scan fires the electron stream in a series of zigzag lines that starts in the upper left-hand corner and moves left to right and top to bottom. It is repeated to maintain the image as the phosphor only glows for a short time. This is called refreshing. Interlaced monitors speed up refreshing by first scanning the odd lines from top to bottom and then scanning the even lines. However, this can cause the monitor to flicker. Non-interlaced monitors refresh the screen by scanning every line at up to 72 times every second. When the screen is being altered, only the data that is changed is transmitted. The information that describes the difference between the two screens is called delta information. It is the ‘change’ information.
A special type of CRT display is available to only display vector graphics. Vector display systems direct the electron stream to draw only the lines required for the image. Shading can only be drawn as a series of lines. Vector display systems have a faster refresh rate than CRT displays using a raster scan.
LCDs (liquid crystal displays) are a flat screen. They consist of a layer of liquid crystal material placed between two polarising sheets. Light is passed through the liquid crystal material, and current is applied at particular point s. LCD technology provides displays that
are very light, take up less room, produce no heat, have no glare, and create no radiation. Furthermore, LCDs require less power than CRTs, allowing them to run on batteries. At present, LCD technology does not produce the same picture quality as CRT technology, and larger displays are more expensive. LCDs are used in portable computers (see Figure 7.14) and
can be mounted on the wall.
Useful Link:
Video Projectors
LCD and DLP projectors.mp4
- These were once extremely expensive and only worked in dark rooms, however one thing has changed, that is the display no longer require a dark room and picture quality is much higher
- Three types of projector exist: Three guns: Each gun for R,G, and B colours, these may produce the most light output but they are highly expensive. DLP: uses a tiny multifaceted mirror chip to reflect light from a light source. Each mirror is controlled by supplying a TV signal; the chip is then able to create an image which is projected onto the screen.
- LCD-based projectors: perform similarly to LCD screens. Light is passed through and LCD before being projected onto a screen.
Plasma
Plasma TV
- Plasma creates red, green, and blue lights in every pixel, reducing the need for space.
- Charged electrodes between two glass panels react with tiny particles of inert gas.
- The gas changes to state of plasma, resulting in UV light, which then reacts with RGB phosphor in each pixel to emit visible light.
- The image compared to dull LCD makes it sharper and brighter. And unlike CRT’s or LCD’s needs not be located far away from peripheral speakers as magnetic fields don’t affect it.
- However its processing ability is slower than LCD and has difficulty focusing on fast moving objects, often having a trailing effect. Plasma requires a lot of electricity run consequently producing mass heat, and has a limited lifespan of 30,000 hours.
Touch Screens
Touch screen
- Is a VDU sensitive to human touch, allowing the user to interact with the computer by touching the pictures or words on the screen.
- Resistive – the screen panel is coated with a thin metallic, electrically conductive and resistive layer. When the panel is touched it causes a change in the electrical current which registers as a ‘touch’ and is sent to the controller for processing the response.
- Surface wave – uses ultrasonic waves that pass over the touch screen panel. When the panel is touched, a portion of the wave is absorbed. This change in the ultrasonic waves registers the position of the ‘touch’ and sends this info. to the controller for processing.
- Capacitive – this is coated with a material that stores electrical charges. When the panel is touched, a small amount of charge is drawn to the point of contact. Circuits located at each corner of the panel measure the charge and send the info. to the controller for processing.
Speakers
speakers.mp4
- Speakers are devices used to produce sounds.
- Audio signals from a computer are translated into analog sound waves for transmission through the speakers.
- The sound is generated electromagnetically. A coil of wire is attached to a cone or diaphragm.
- The coil is placed around a permanent magnet, so that an electronic signal passing through the coil magnetises it.
- As the coil is magnetised, it pulls and pushes against the permanent magnet, causing the cone to vibrate according to the strength of the electronic signal.
- The movement of the cone makes the air near the cone vibrate, and this creates sound waves.
- Sound has become a vital part of multimedia use.
- It is the sound card that determines the quality, not the speakers.
How CD's store data
How a cd stores data.mp4
Head sets and Heads up displays
Project Glass: One day...
YouTube Video
- VR often use a headset to impose the perception of reality directly to their visual senses.
- Two VDU’s are used, each constituting one side of the glasses, and each presenting a slightly altered view than the other. When the two are combined a 3D image is presented.
- Heads up displays are smaller, less intrusive, and were developed by the military. The screen is transparent so forward view is not affected.
Hardware to collect / display Animation
- Common hardware used to collect / display animation data:
- Scanners (flatbed, hand held, drum, pen)
- Digital Video Cameras
- Digital Cameras
Calculating animation file sizes
* Remember 2 bit depth = colours or shades available
* File size in bits = height x width x bit depth x frames per second x time in seconds
* Eg an animation is 300 x 400 with 4 colours and plays at 24 fps over 20 seconds
2 bit depth = 4
Bit depth = 2
File size in bits = Resolution x bit depth x frames per second x seconds of play
= 300 x 400 x 2 x 24 x 20
= 115,200,000 bits
= 14,400, 000 bytes
= 14062.5 kilobytes