4.Describe various types of touch screens and explain how a touch-sensitive

  

      A touchscreen is an electronic visual display that can detect the presence and location of a touch within the display area. The term generally refers to touching the display of the device with a finger or hand. Touchscreens can also sense other passive objects, such as a stylus. Touchscreens are common in devices such as all-in-one computers, tablet computers, and smartphones.

The touchscreen has two main attributes. First, it enables one to interact directly with what is displayed, rather than indirectly with a pointer controlled by a mouse or touchpad. Secondly, it lets one do so without requiring any intermediate device that would need to be held in the hand. Such displays can be attached to computers, or to networks as terminals. They also play a prominent role in the design of digital appliances such as the personal digital assistant (PDA), satellite navigation devices, mobile phones, and video games.

Ergonomics and usage

Finger stress

An ergonomic problem of certain types of (resistive) touchscreens is their stress on human fingers when used for more than a few minutes at a time, as significant pressure can be required, depending upon the technologies involved. This can be alleviated for some users with the use of a pen or other device to add leverage and more accurate pointing. The introduction of such items can sometimes be problematic, depending on the desired use (e.g., public kiosks such as ATMs). Also, more accurate control is achieved with a stylus, because a finger is a rather broad and ambiguous point of contact with the screen itself, but requires the user to possess fine motor skills to hold such a stylus.

Fingernail as stylus

These ergonomic issues of direct touch can be bypassed by using a different technique, provided that the user's fingernails are either short or sufficiently long. Rather than pressing with the soft skin of an outstretched fingertip, the finger is curled over, so that the tip of a fingernail can be used instead. This method does not work on capacitive touchscreens.

The fingernail's hard, curved surface contacts the touchscreen at one very small point. Therefore, much less finger pressure is needed, much greater precision is possible (approaching that of a stylus, with a little experience), much less skin oil is smeared onto the screen, and the fingernail can be silently moved across the screen with very little resistance,allowing for selecting text, moving windows, or drawing lines.

The human fingernail consists of keratin which has a hardness and smoothness similar to the tip of a stylus (and so will not typically scratch a touchscreen). Alternatively, very short stylus tips are available, which slip right onto the end of a finger; this increases visibility of the contact point with the screen.

Fingerprints

Touchscreens can suffer from the problem of fingerprints on the display. This can be mitigated by the use of materials with optical coatings designed to reduce the visible effects of fingerprint oils, or oleophobic coatings as used in the iPhone 3G S, which lessen the actual amount of oil residue, or by reducing skin contact by using a fingernail or stylus.

Combined with haptics

The user experience with touchscreens without tactile feedback or haptics can be difficult due to latency or other factors. Research from the University of Glasgow Scotland [Brewster, Chohan, and Brown 2007] demonstrates that sample users reduce input errors (20%), increase input speed (20%), and lower their cognitive load (40%) when touchscreens are combined with haptics or tactile feedback [vs. non-haptic touchscreens].

Gorilla arm

The Jargon File dictionary of hacker slang defined "gorilla arm" as the failure to understand the ergonomics of vertically mounted touchscreens for prolonged use. The proposition is that the human arm held in an unsupported horizontal position rapidly becomes fatigued and painful, the so-called "gorilla arm". It is often cited as a prima facie example of what not to do in ergonomics. Vertical touchscreens still dominate in applications such as ATMs and data kiosks in which the usage is too brief to be an ergonomic problem.^[

Discomfort might be caused by previous poor posture and atrophied muscular systems caused by limited physical exercise. Fine art painters are also often subject to neck and shoulder pains due to their posture and the repetitiveness of their movements while painting.

Screen protectors

Some touchscreens, primarily those employed in smartphones, use transparent plastic protectors to prevent any scratches that might be caused by day-to-day use from becoming permanent.