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[edit] Screen Definitions
[edit] DISPLAY CONTRAST RATIO
A high contrast ratio is a desirable feature on any display. By definition, contrast ratio measures the luminosity of the brightest and darkest color that an LCD can display. If a display has a poor contrast ratio there will be a lack of true black and desaturated colors.
There are a variety of methods that can be used to measure a display's contrast ratio and each of these methods can provide a wide array of results for the same display. A typical contrast ratio may be noted as 1000:1 or 100:1. The larger number will result in the best contrast. Display manufacturers and designers prefer different methods of measurements.
Manufacturers measure the contrast ratio based on methods that isolate the display from the system, whereas, designers prefer methods that allow them to factor in the room effect. Ideally a room absorbs all light and the only light displayed would be from the monitor, however, in actual rooms some of the light is reflected back to the display which effectively decreases the contrast ratio.
To further complicate contrast ratio measurements, one must consider both static and dynamic contrast ratios. The static ratio only considers luminosity levels at a single instance in time, whereas, the dynamic ratio considers the luminosity the monitor displays over a period of time. This may be thought of more simply by referring to the static ratio as measuring a static image and the dynamic ratio by considering the affects of a more dynamic or moving image.
Ideal Room Measurement
This type of measurement is typical of manufacturers because it results in the highest possible contrast ratios. This is done by keeping the room at optimum conditions so that the reflective light remains constant. Testing in this manner has no affect on luminance levels, however, it does inflate the light levels.
Real Room Measurement
Contras ratios are more realistic when measured in real rooms that expose the display to conditions where some light is reflected back to the display. ANSI contrast simultaneously measures luminosity values using a checker board patterned test image.
Optimal and Degraded
The Ideal Room Measurement (full on/full off) measurement method effectively measures the dynamic contrast ratio of a display, while the Real Room Measurement (ANSI contrast) is best used to measure static contrast ratio.
Comparing dynamic and static contrast ratios is similar to one trying to compare apples and oranges. These items should never be directly compared. Some manufactures choose to market only the dynamic contrast ratio when the result is better than the display's static ratio. A display with a static contrast ratio of 10000:1 is a much better display than one with a 10000:1 dynamic and 5000:1 static contrast ratio when the input signal contains full range of brightness' from 0 to 100% simultaneously. However the displays will be equal when the input signal range is decreased to a 0 to 20% brightness level.
In order to achieve optimum contrast ratio results, displays are typically measured in completely dark rooms. It will be nearly impossible to achieve these same results during normal viewing conditions. The reduction in contrast ratio will depend on the display luminance and the reflective light in the room.
[edit] Types of Touchscreens
Capacitive Touch Screens
Touch Screen Display MonitorCapacitive touch screen technology is recommended for use within KIOSK applications that require a "finger touch". It will not operate with either a gloved hand or with a mechanical stylus. It is made of glass, which makes it extremely durable and scratch resistant. This glass overlay has a coating that stores the charge deposited over its surface electrically. Capacitive touchscreens operate using oscillator circuits that are located in each corner of the glass overlay and measure the capacitance of the area being "touched". Depending on where the person touches the overlay, the oscillators will vary in frequency. Then a touchscreen controller measures the frequency variations to ascertain the coordinates of the person's touch. When used with flat panel displays, capacitive offers drift-free stable performance that is not susceptible to deterioration over time. A capacitive touch screen is impervious to grease, dirt and water, which makes it ideal for frequent use. It can also be gasket sealed for NEMA 4 and NEMA 4X operation. Since a capacitive touchscreen is made of glass, it is susceptible to breakage.
Anti-Glare Resistive Touch Screens
Resistive touch screen technology is recommended for use in POS (Point of Sale): Grocery Stores, Hotels, Restaurants and Retail Stores; Industrial Applications: MMI (Man Machine Interface), Machine and Process Control; Portable Devices; Personal Information Management Systems; Transportation Solutions; Medical Solutions: Equipment, Instrumentation and Patient Monitoring Systems. Industrial Touch Screen MonitorResistive technology generally uses a display overlay composed of layers, each with a conductive coating on the interior surface. Special separator "dots" are distributed evenly across the active area and separate the conductive interior layers. The pressure from using either a mechanical stylus or finger produces an internal electrical contact at the "action point" which supplies the controller with vertical and horizontal analog voltages for data input. To reduce parallax for older "curved" CRT applications only, resistive touchscreens are generally spherical to match the curvature of the CRT (true flat resistive touch overlays are also available for TFT flat panels and/or CRTs). Our resistive touchscreens are anti-glare to reduce reflective shine intensity, which will slightly diffuse the light output throughout the screen. Resistive technology offers tremendous versatility in that activation can be initiated by; a gloved hand, fingernail, mechanical stylus or an ungloved finger. Resistive touch screens can be gasket sealed for NEMA 4 and NEMA 4X environments. Limitations include: Low light output, diffused resolution images and the a plastic surface material can be scratched if improperly touched. VarTech offers a variety of resistive touch screen displays many are available with an optional sunlight readable touch screen.
Near Field Imaging or NFI touch screens
Indistrial Touch Screen LCD Flat PanelNFI touch screens are ideal for washdown environments and other applications where extreme durability is required. The construction of NFI touchscreens allows them to withstand shock and virbration environments. Common surface contaminants found in industrial environments will not effect the touch screen. NFI touch screens have the ability to detect touches made by conductive objects, such as, a finger or stylus pen. As an added benefit these touches can be detected through gloves and other potential barriers, such as, moisture, oil, gels and paints.
Infrared Touch Screens
Infrared touch screen technology is based on "legacy" technology and is becoming increasingly replaced by Resistive or Capacitive touch systems. Over the years, Infrared bezels have proven to be a very reliable technology for use in ATMs, Food Service and Preparation, KIOSK, Medical Instrumentation, Process Control Systems and Transportation Tracking applications. It does not incorporate any sort of "overlay" that could inhibit screen clarity or brightness, but instead, uses a special bezel of LEDs (light emitting diodes) along with diametrically opposing phototransistor detectors, which surround the glass of the display surface. The controller circuitry scans the screen with an invisible lattice of infra-red light beams just in front of the surface that directs a sequence of pulses to the LED's. It then detects information at the location where the LEDs have become interrupted by a stylus or finger. The infrared frame housing the transmitters can impose design constraints on operator interface products. A few limitations are (1) that they usually require low-resolution output of the monitor, (2) can produce activation without touching the screen and (3) the cost to produce the special Infrared bezel is quite high.
Surface Acoustic Wave (SAW)
SAW touch screen technology is suggested for use in ATMs, Amusement Parks, Banking and Financial Applications, Gaming Environments, Industrial Control Rooms and KIOSK. SAW touch cannot be used within NEMA environments, as the technology cannot be gasket sealed. It has excellent durability that allows it to continue working if scratched since the overlay for the touch sensor is a solid glass display. The disadvantage to this glass overlay is that is breakable and won't work in washdown conditions. The waves are spread across the screen by bouncing off reflector arrays along the edges of the overlay and are detected by two "receivers". The acoustic wave weakens when the user touches the glass with their finger, gloved hand or soft stylus. The coordinates are then determined by the controller circuitry that measures the time at which the amplitude declines. It is the only technology that can produce a Z-coordinate axis response. SAW technology offers drift-free stable performance that is always precise. SAW offers superior image clarity, resolution and high light transmission.
Projected Capacitive touch screens
Projected Capacitive touch screens have changed the world of touch screen monitors. This new evolution of the touch screen monitor allows touches to be sensed through a protective layer in front of a display. This allows touch screens to be installed behind windows or other protective glass. The most exciting aspect of the projected capacitive touch screen is that it is the only touch screen that is acceptable in Class 1 Div 1 or Div 2 environments. Since there is a protective covering installed over the actual monitor and the actual touch sensor is embedded, the chance of a charge being created as the touch screen is used has been eliminated. The complete system resists impacts, scratches, and vandalism. It is also unaffected by moisture, heat, rain, snow and ice or harsh cleaning fluids, making it ideal for outdoor applications. Projected Capacitive touchscreens are ideally suite for use throughout a wide variety of applications, such as, outdoor kiosks, ATMs, pay-at-the-pump and Class 1 Div 1 and Div 2 environments.
Optical Imaging Touch Screens
Optical Imaging touch screen technology revolutionizes the way we interface with computer technology. Unlike many touch screen displays, the entire screen, corners included, is sensitive to the touch. This technology uses optical components. No surface coatings are used on the screens - hence images are kept crystal clear. Any method can be used to touch the screen: a finger, a gloved hand or any pointer. Only a light touch is required. Optical imaging technology provides touch sensitivity over the whole screen, including the corners. With over 400,000 touch points, accuracy is guaranteed. Optical imaging technology touch screens are calibrated just once at commissioning time. The technology provides continuous operation with no drift, no need to recalibrate. Because optical imaging technology solutions don't employ surface coatings, the customer-facing screen is not affected by scratches or contamination. Also, the products can be easily sealed for resistance to dirt, dust and moisture, making them ideal for demanding public environments. The modular touch screen system can be replaced in the event of failure or damage, provides two-touch capability, middle mouse-key scrolling and object size recognition. Diagnostic utilities are also available. VarTech’s optical imaging touch solutions do not require special software drivers; they incorporate HID compliant USB plug-and-play interfaces.
