Touch Me!

click here to read this article in ProSystems Africa News magazine July/August 2016.

These days the words ‘screen’ and ‘touch’ go together like bacon and eggs. It’s nothing new to touch a display screen and expect a relevant response. Consumer grade mobile phones, tablets and most notebooks are all touch-enabled. Interacting with a display has become part of our daily lives.

Many moons ago the idea of touching a display to initiate a command was only known from Hollywood sci-fi. Touch Screen technologies have been experimented with from as early as the late 1960s. However it was only around the turn of the century that we saw touch enabled point of sale systems and interactive information kiosks become more customary in retail spaces. High-end meeting and conference venues utilized state of the art touch overlays over LCD and plasma screens, and back then homes-of-the-future had touch panels with processors controlling their environments. Interactive projection also grew in prevalence, but has never entertained the same levels of attention as touch LCD screens. In the case of interactive projection, ultra-short throw projectors are paired with infra-red or radar devices which cast a separate grid over a projected image. A stylus pen or finger is then used to interact with the grid on a solid surface such as a white board with a low reflective surface.

LCD touch technologies have seen many iterations over the years. Each variation of touch screen architecture focused on the key features - accurate touch and near instant response time - but with an objective of improving a previous result. The biggest challenge in any touch technology is for interaction to be acknowledged by the system and then another challenge is to determine the precise location of the touch on the screen.

The aesthetics of modern day touch overlays such as capacitive and resistive technologies used in smart phones, tablets and kiosks mask very well any visible hint of external technologies. Capacitive Touch screens consist of a conductive coating over a transparent insulator, such as glass. The human body, being an electrical conductor itself, then disturbs the screen’s electrostatic field when touching it. Many variations of capacitive technologies are available, but essentially these function in a similar way. A grid array of sensors is continuously scanned to determine the location of the touch. Resistive Touch screens consist of two layers, each with a fine grid of conductive material placed over each other with a micro cavity in between. The top layer is typically softer, and, when pressed down, makes contact with the bottom layer. A short-circuit registers a resistance in the voltage which will indicate a touch. The X and Y coordinates of the grid determines the location. Not all touch screens are as smooth looking. Alternative technologies have equipment integrated into the bezel of the screen, with protective glass covering the display surface. Because of the integration in the bezel, the latter sits proud from the display surface and could be perceived as a bulky finish.

Surface Acoustic Wave (SAW) and Dispersive Signal Touch (DST) are vastly different technologies but both utilize wave interference by finger touch. SAW systems emit ultrasonic waves over a display from two sides and then measure the same waves from the remaining two sides. An object interfering with these waves will absorb a percentage of the energy and the relevant touch controller then measures the change in amplitude in order to determine the touch location.  DST in turn, measures the bending waves created by a finger touching a display surface from all around the surface area. This is similar to the ripple effect of a water surface when disturbed. Neither of these technologies is very popular because of substantial interference of surface particles such as dust or humidity.

Infra-red (IR) touch systems have IR emitters and sensors around the bezel of the display to form a grid in front of the touch surface. When touched, one or more light paths are broken and based on XY coordinates, a touch, and its location, is registered. Optical Touch systems have LED lights integrated into the bezel, which creates an invisible light layer over the display area. Two cameras from the top corners are monitoring disturbance in the light plane and thus determine touch and location. These technologies do not perform well in very bright environments.

Shadow Sense Touch (SST) is the newest kid on the block. LED lights are integrated into the sides and bottom of a display bezel, with optical sensors in the top corners and top bezel. These sensors measure a shadow created by the interference of a light path. Because of SST architecture being positioned in the bezel, the product, like other optical touch technologies, is also available as a video wall over-frame kit. Individual bezel pieces are mounted around the perimeter displays in a video wall up to 6m in width. These bezels then function collectively to create a touch capable video wall.

SST not only determines a touch and its location, but also identifies the shape of the touch-object used. Software then allows the user to configure a set of parameters in order to accept certain shapes, and ignore others. This feature revolutionized the world of annotations because fingers and pens can be recognized, whilst suit cuffs and hand palms can be dismissed. This in turn reduces headaches, frustration and violence in the workplace.

OLED: Flattering flat panels

Article published in ProSystems Africa News magazine May/June 2016 edition.
Access on ProSystems Africa News Site

From the late twentieth century onwards we have all witnessed the revolution in TV set technology. Display screens have undergone a noteworthy evolution, in which square box television sets changed to wide rectangular ones, then to flat plasma displays although they weren’t actually flat but only labeled as such in reference to what they used to be. Plasma display panels (PDP) were succeeded by LCD technology which wasn’t much thinner than their predecessor. Only when the compact fluorescent light source got upgraded to LED, did the thickness reduce tremendously. For many years, these LED-lit, LCD panels were the flavour of the month and they increased in either brightness or resolution as new and improved models were released. With each of these technological breakthroughs our minds were blown away and the screens became more appealing every time. Even upgrades within existing technologies were impressive. The next level of display innovation has arrived and recently came to light through many well-known manufacturers at ISE2016. This new technology is known as Organic LED (Light Emitting Diode), more commonly abbreviated to OLED.

Organic LED as a display technology is nothing new. Many film and video production institutions have been experimenting with it for many years. However, it has only recently become available as residential and commercial displays. The OLED display screen is a light emitting technology and therefore doesn’t need a separate light source behind the screen as is required in LCD panels. They can thus be manufactured much thinner than ever before. LCD screens are classed as a transmissive technology, which essentially means that the LCD display merely transmits the light from a separate light source behind the LCD screen. Each pixel in the LCD panel then individually disperses the white light into the three primary RGB (Red, Green and Blue) colours at various intensities in order to display the correct mixture of light required to reproduce the image visible to the viewer. The architecture of these LCD panels requires a screen in front, as well as a light source behind it which adds to the thickness.

In contrast to conventional light sources which emit light by heating a filament until it glows while hot, LEDs are a semi-conducting, solid state light source that require far less energy to produce light. LEDs emit light when electrons are energised through specially treated solid materials that the LEDs are made of. Through this sub-atomic process, low voltage pulses initiate electron movement further away from its proton core and when the energy dissipates, the electron jolts to its original position. During this twitch, alternative energy is released in the form of light. Depending on the length of electron movement, different colours can be created based on the colour spectrum. Organic LEDs are similar to traditional LEDs but the light is produced by organic molecules. In this environment the term ‘organic’ refers to the molecules around the rings of atoms in carbon elements such as wood, plants, petroleum and diamonds. As mentioned above, OLED technology emits its own light and therefore does not require a separate light source. This enables the OLED display products to be extremely thin.

Plasma displays have finally reached the golden years and it has become increasingly difficult to purchase one. PDP is also an emissive technology as the ionized gasses inside the screen emit light. The plasma imaging technology has extremely high thermal emissions albeit very bright and therefore sufficient cooling components are required behind the plasma panel which adds to their thickness. Another downside for PDP is that they consume high levels of energy and the panels are physically very heavy to handle and install. PDP technology has each pixel subdivided into three segments. Each of these sub-pixels is filled with different colour (RGB) phosphor-coated cells which illuminate when energized. The three colours combined at 100% intensity, or variations thereof create the full colour spectrum that forms the image which the viewer can then experience. Plasma display panels have their benefits as well. Because of the panel emitting the light, the black areas were darker, delivering higher contrast between lit and unlit areas. LCD panels have a challenge in this regard as the light source at the back is present even when a pixel is blacked out. This results in black areas appearing dark grey instead of true black. Plasma displays are also capable of delivering very high brightness levels and can be produced in large sizes. However none of these benefits could save its obsolescence.

The imaging technology in OLED displays works by means of a layer of organic semiconductor between two electrodes which emits light in response to electric current. The OLED pixel composition works in a similar pattern to that of a plasma display with each pixel subdivided into three sub-pixels. These are known as RGB OLED displays and each segment contains an organic diode which produces one of the primary RGB colours. Certain manufacturers use WRGB (white, red, green and blue) technology where each pixel is divided into four sub-pixels instead of three. The fourth segment produces white light only, but in order to create white light, one requires a 100% mixture of each of the RGB colours. The architecture to achieve this white segment works somewhat differently to RGB OLED. 

In the case of WRGB OLED, each segment of the pixel is created by compressing different layers of red, green and blue diodes. This sandwich of materials then creates a pixel with four segments delivering white light. A colour filter is applied to the surface area of three of the white segments creating the required RGB light and the fourth segment is left clear for the white light to be visible.

This fourth sub-pixel makes the technology even more energy efficient as it requires only one LED to produce white instead of a combination of the RGB LEDs to deliver the same objective. This results in an energy saving of roughly 60%. Another benefit of having a fourth pure white sub-pixel is the increased brightness when used in conjunction with the remaining RGB LEDs to produce whiter images. OLED displays also offer a much higher contrast as black areas can be completely switched off - as in the case of plasma technology - compared to the light leakage experienced in LCD screens. Additional benefits of OLED are lower thermal emissions and because of the properties of the organic diodes, they can be applied to all kinds of surfaces that make it possible for OLED screens to be lighter, thinner, flexible (bendable and foldable) and generally more durable. OLEDs can also operate in a wider temperature field than older technologies.

OLED products are currently still very expensive but based on the statistics around the costs of developing and producing electronics, pricing can only go one way from here and hopefully, OLED displays will be part of every video project sooner than we can imagine.