Computer Output Channels

Output channels of computers take many forms ranging from display screens to simply printing on paper. In this section, we will take a look at a few different output channels and how they work.

Display screens

A display screen is an output device used for the visual presentation of information. It is the most commonly used device in computer monitors and televisions.

Bitmap display

The resolution defines the precision of the display content. There are two properties that define the resolution of a screen:

• Total number of pixels: Presented as width x height in the unit pixels. The most commonly used aspect ratioAn image’s width into height ratio. is 4:3.

• Pixel density: The number of pixels per unit distance. Presented in the unit PPI.

Note: The greater the number of pixels, the better the image quality, but at the expense of larger file size. Also, human vision capability is limited to a certain number of pixels. Beyond this number, humans cannot perceive any difference in quality.

But there is a potential problem with the bitmap display. Look at the image below, do you see the sharp edges of the lines? This happens with every line we draw at any angle other than vertical or horizontal. These sharp edges are called Jaggies.

Jaggies: Jaggies are a display anomaly often seen as a staircase of sharp small squares in place of smooth curves and lines.

This problem can be solved by using either high-resolution screens or anti-aliasing.

• High-resolution: High-resolution means a large number of pixels and less compression.

• Anti-aliasing: A technique that blurs this discontinuity by softening the sharp edges.

Underlying technologies

Let’s have a look at some underlying technologies used for most displays.

• CRT: CRT (Cathode Ray Tube) was the most commonly used technology for the longest time in history. CRT monitors have a vacuum tube with a fluorescent screen at one end and an electron gun at the other. Images are formed by projecting a high-intensity beam of electrons ejected from the electron gun on the fluorescent screen. These monitors are bulky and heavy. Their usage decreased when lighter, more compact monitors were developed.
• LCD: LCD (Liquid Crystal Display) is one of the most advanced technologies used in screens. Liquid crystals have light-modulating propertiesThe modulation of electromagnetic radiation in the optical region.. This technology uses these properties to display arbitrary images on the screen. An LCD monitor has a liquid crystal in the center with transparent electrodes and polarizing filters on both sides. Images are formed when light is passed from the polarizing filter all the way to the crystal layer. LCD monitors are ideal for laptops due to their compact size and less consumption of electricity as compared to CRT monitors.
• LED: LED (Light Emitting Diode) is also one of the most advanced technologies and better than LCD. It uses light-emitting diodes for backlighting and produces better images with higher contrast. They are either flat or slightly curved panel displays. This is a better option for less energy consumption and thinner design as well.
• PDP: PDP (Plasma Display Panel) uses small cells filled with plasma. Plasma is an ionized gas that can be used as a light source. Plasma is responsive to the presence of electromagnetic fields and becomes highly conductive. PDPs are widely used in large displays and high definition displays.
• Electronic paper: Electronic paper is a display device that reflects light like an ordinary paper rather than emitting light. Electronic paper is more comfortable to read from and has a wider viewing angle compared to other technologies. Electronic paper is used mostly in digital bus stop signs, electronic menu boards at restaurants and cafes, and electronic display of prices at oil and gas stations.

Auditory displays

Auditory displays are used for presenting information in the form of sound. Sonification is the representation of information and data in the form of both visual and auditory sounds. The applications of sonification include human-computer interfaces, data analysis, information systems for visually impaired people, and as an alternative to visual displays. Sonification is an umbrella term for many different techniques. A few of them that are used in HCI are listed below.

• Audification: Audification is the mapping of raw data into non-speech sound waves by mapping the data values to sound pressure levels. Each data set is given a different sound value. For example, an ECG machine converts the electrical signals received from the heart into both visual and auditory soundwaves. Here are some more applications of audification:

  • Electronic music
  • Stethoscope
  • Auditory ultrasound
  • Earthquake prediction

  Sonification sandbox is a software that converts data into auditory signals. Here is a demo video of how it works to give you a clear understanding. The default example that comes with the software when you install it has been used in this demo.

• Earcons: This is the representation of an event or a result of an action in the form of a brief musical sound.

• Auditory displays: This is the representation of an event or a result of an action in the form of an everyday natural sound.

• Voice messaging: Voice messaging is another technique of sonification that converts recorded speech to its equivalent text. The same concept is used in text-to-speech conversion.

Printers

Printers are very common output devices that print the information on paper. They take the digital data and information and output it in the form of a hard copy.