There are many technologies for large display touch-screens. Some are proprietary so only available from one source, and others like PCAP (Projected Capacitive) and IR (infra-red) are available from many suppliers. For people wanting to use a stylus none of these fully replicates the responsiveness and feel of pen and paper (*see note at end) but that is not a requirement for most large touch-screen applications.
PRICE
Touch technology adds quite a lot to the cost of a large monitor. IR is typically the lowest cost, then PCAP and then others – however you generally get what you pay for depending on your criteria.
MULTI-TOUCH
Every large touch-screen I see seems to be multi-touch (this refers to how many simultaneous touches can be detected and tracked at the same time), however very importantly it does not mean the software application makes use of this capability, it may not be necessary.
- Single touch: Suitable for applications where there is a button choice or single touch panning, for example on ATM machines and many public kiosk-type applications.
- 2 point multi-touch: Any application that requires two finger zooming, so examples might include way-finding, mapping and other image related applications. Thanks to smartphones and tablets many people are familiar with two finger touch functions, and depending on the application they are quite likely to expect this capability.
- More than 2 point multi-touch: In trade shows it is quite normal to see a touch-screen salesperson dragging ten fingers across a large touch screen running a graphics application to demonstrate 10 point multi-touch, but that is typically where the requirement stops. Very few applications (other than these drawing programs) provide any meaningful support for 3 or more point multi-touch, and if they do then users are unlikely to recall them. Two possible exceptions:
- Object recognition: This typically works on the basis of multi-point pads that the touch-screen can detect and the software interpret.
- Gaming: A casino-type touch-screen table game is very likely to have any number of users and simultaneous touches and the software and hardware to support it.
RESPONSIVENESS
There are two times people tend to notice poor responsiveness:
- Pressing a button for some interactivity then takes too long: The usual causes of this are either the software application or an underpowered PC.
- When drawing a line the visible line lags behind the user’s finger or stylus: This is the most demanding example and every part of the system, from touch technology, the PC, the display, and the software can impact this.
BEZEL – FLAT OR RAISED
Smartphones and tablets have flat fronts, there is no raised bezel. Large IR touch-screens have raised bezels whereas other touch technologies typically don’t, ie., if a touch screen has a raised bezel it is very likely to be IR based; gaming touch table may be an exception. Possible issues with raised bezels:
- The bezels collect dirt and need cleaning to prevent obstruction of the IR LED’s transmitters or sensors. This can impact reliability.
- Not as attractive as a fully flat display, in my opinion.
- Possibly restricted access to the very edges of the display. This can be an issue for Windows users in corporate applications.
AESTHETICS
For some users the presence of a raised bezel is more than just a concern over dust collection and the need for cleaning. It is also less appealing aesthetically – they prefer the completely flat surface like that of a tablet.
- No raised bezel, ie., completely flat: PCAP, acoustic wave and some proprietary technologies like the version of Flatfrog’s InGlass that we use.
- Raised bezels: IR, camera and laser type touch technologies.
STYLUS USE
Large and small touch-screens face a particular challenge when it comes to using a stylus and that is everyone’s experience with pen and paper. Touch-screens do not replicate the feel of pen on paper. There are a few considerations with stylus use:
- Type of stylus:
- Passive: This can be a piece of wood, basically anything can be used. IR and similar technologies can typically work with passive styluses. PCAP can usually support passive styluses made with a suitable conductive material.
- Active: These styluses use batteries and when turned on create a field that the PCAP can detect. I got reliable results using a 1.4mm active stylus with a 55″ PCAP display in our engineering.
- Responsiveness: Writing or drawing using a stylus will quickly reveal latency (delay / lag) in the touch-screen system which may be due to the touch technology, the display, the PC or the software.
- Feeling: The material of the stylus tip seems to be the most important, although the surface finish on the cover glass is bound to have some impact. Too hard a stylus on a totally smooth cover glass feels hard and scratchy, and if the stylus tip is too rubbery it will have a slightly sticky feeling.
- Resolution: Stylus tip size, as a test I purchased the finest tip active stylus I could find online – a 1.4mm designed for Android smartphone and tablet devices. It worked very well with our engineering sample PCAP monitor (55″).
- Accuracy: Various factors to consider, the resolution of the touch-screen, the size of the stylus tip, the resolution of the display, the software and parallax.
- Parallax: I have a separate note on this below but parallax is most acute when using a stylus because the tip of a stylus is finer than the tip of a finger, so the misalignment is most noticeable.
- Palm rejection: The best I have seen with a large touch-screen is with PCAP but it did not seem completely reliable when working with a stylus.
FALSE TOUCH
Some touch technologies detect touches above the surface of the cover glass, notable examples are IR and PCAP. False touches can be really frustrating as some users may even notice the display react before they feel they have touched the screen. This is more important when using a stylus as it will show lines or marks when they were not intended. ‘No false touches’ is one of the selling points of our F-line series (42″, 55″, 65″) as the InGlass touch technology we use in those touch-screen monitors only detects when the user actually touches the cover glass surface.
PALM REJECTION
A hardware / software issue. The main point is to avoid false touches from people resting the palm of their hand or sleeve on the touch-screen. Some technologies support this, notably PCAP
CLARITY / LIGHT TRANSMISSIVITY
The greatest clarity is going to come from a low iron glass with no coatings, films, layers or wires. Our F-line monitors meet this high standard of clarity and it is also possible with IR but it depends on the cover glass chosen. PCAP touch displays cannot achieve the same clarity as they use either of the following:
- An ITO (Indium Tin Oxide) layer, this is a transparent metal layer that may reduce the light transmissivity by about 20%; or
- Wires arranged in a pattern. Some designs are quite visible but others are only visible to keen observers.
REFLECTION
There are two principle finishes to the cover glass that will impact the image:
- AR (Anti-Reflective): This is a coating that can be applied to one or both sides of the cover glass to reduce certain frequencies in the light and minimize the effect of reflections. It is often noticeable by a slight purplish tinge when viewed from some angles. As far as I know all touch technologies can make use of AR coatings but it is the most expensive so not many systems have it.
- AG (Anti-Glare): This is a diffusion finish on the cover glass. It is the lowest cost and is quite effective at reducing reflection, but it will soften or slightly blur the image and can also add a slight color sparkle, This is more of an issue to touch users, especially with higher resolution displays and less of an issue for viewers in presentation systems. I am not in favor of AG finishes because of the impact on the image. I should note that normal desktop monitors usually have an AG finish but as the surface of the display is closer to the image the diffusion effect is less noticeable.
If reflection is not an issue then clear glass will give the sharpest image result.
Note, all displays have polarizers in them which can impact the brightness of the display if viewed with polarized sunglasses from certain angles. Some outdoor displays use a circular polarizer to as to minimize this – it is not related to the touch screen cover glass.
PARALLAX
This is an issue most people notice quickly, especially if they are using a stylus. It refers to the difference between where the user sees they are touching and where the touch screen/display actually detects. It arises when the touch surface is sufficiently far from the image surface and the user is looking from an angle. Factors that affect this:
- The distance from the surface of the touch detection to the display image surface. I chose my words carefully because some technologies, notably IR and PCAP detect ‘touches’ above the surface of the cover glass (see False Touch above). I have never seen a touch-screen supplier give the specification for this and it seems it would be hard to measure reliably. Some technology factors:
- Distance the touch technology needs to be above the surface of the display. For example some wire- type PCAP technologies need a gap to avoid interference.
- Thickness of cover glass. As a note, IR touch-screens have a cover glass for protection but not as part of the technology.
- Detection height. IR and PCAP both detect above the glass. Some companies fine tune this to minimize the height, while other technologies require actual contact with the cover glass.
- The resolution of the application, so an application with large buttons is not likely going to have any noticeable parallax issues even if there is a bigger gap between the touch surface and the image surface.
*PEN & PAPER
There are a number of small screen developments where the pen & paper experience is getting close; the tablet by Remarkable is one that does a pretty good job.