Ultra Large 4K Touchscreens?

4K is a Natural Fit for Large Touchscreens.

The market will likely demand 4K resolution touchscreens for ultra large displays. The price has dropped on the 4K panels while the combination of an Ultra High resolution 4K display and a touchscreen is a natural fit. The detail is so great and the content is so compelling, that with arm length viewing distances users expect the pixel density to be comparable to their smart phones and tablets. These UHD 4K touchscreens will bring viewers even closer offering an immersive interactive experience for which application providers are just now beginning to embrace.

The Ultra HD displays are an impressive work of technical achievement. Unlike other attempts by display manufacturers to jump start lagging sales with new features, the Ultra HD displays appear to be here to stay and there is increasing market acceptance especially as prices continue to drop. The displays now offer four times the resolution of Full HD (at 1920 x1080) with over 8.2 million pixels – that’s 400% more pixels than full HD! The displays offer significant improvements in pixel density and with more pixels comes substantial enhancements in detail at close viewing distances. The video enthusiast sitting on the couch may not appreciate the pixel density but that’s not where these displays are best used. The level of realism and detail is simply stunning. Even text and fine features are clear and precise at close viewing distances. This all leads to benefits for interactive displays and why visualization applications in corporate, academic and government environments are adopting these displays rapidly.

The HD displays are an extraordinary improvement over the old CRT and at couch viewing distances it is difficult to discern between 720p and 1080p anyways. However, at close range the images become pixelated and the small detail is lost and so interactive displays are primarily used for large graphical applications such as signage, way finding and interactive whiteboards. But none of these applications have really taken off beyond niche market status and the dream of the “killer” interactive large format bonanza has yet to be realized.

Touchscreens are a natural fit for a ULTRA HD display

Unlike 1080p displays which are designed to be viewed at a distance, a touch screen requires an interaction distance of an arm’s length and thus the benefits of increased resolution and smaller pixel pitch size can be fully realized.  But with the higher resolution and speed not all touch screen technologies will match the performance of the display.  Some of the issues include the following:

  • Accuracy: With increased pixel density, precision is even more important since small deviations in positional accuracy become more pronounced on an Ultra HD display;
  • Onscreen Handwriting: What affects smooth onscreen handwriting is speed and resolution and the bigger the display, the more data there is to process. Some touch technologies designed for smaller displays do not scale well and will exhibit cursor lag and jagged lines.
  • Multi-Touch – With larger displays there is more opportunity to collaborate with multiple users, making multi-touch beyond just two touch points a requirement and features such as zooming, panning and gestures are all now expected. Most touch technologies are fine for simple point and click applications however, for more feature rich applications such as visualization and collaboration not all touch technologies possess the performance necessary for a good user experience.
  • Image Quality:  Some touch technologies such as projected capacitive require a conductive coating which not only can create a moiré affect but can also shift the color towards a yellow cast.  Only touch technologies that are edged based can provide no undesired display artifacts.
  • USB Power:  Many peripherals are powered using USB, however the number and types of peripherals plugged in to a host PC can have a significant effect on touch screen performance if it is relying on the PC for its sole source of power.

Touchscreen Sample Rate and Display Refresh Rate

One of the most important factors affecting touch screen performance is the touch screen speed known as the touchscreen sample rate or refresh rate. It is the time between consecutive frames of touch data available in the controller buffer measured in frames per second (fps). A low refresh rate will result in jerky movement, jagged lines and curves that appear to be made up of line segments rather than smooth curves. A high refresh rate provides a greater number of data points for interpretation of a smooth or complete shape or motion which translates into improved gesture interpretation and very low latency required for drawing and handwriting applications.

Touch Screen Sample Rate-1In order to do this, a touch screen needs to process the touchscreen data at a higher rate than the display to keep up with the refresh rate of the screen. Making things more complex is that this information needs to be processed for each touch point between scans and that is why multi-touch is very processor intensive.

More touch points means more processing and instead of a more costly controller one solution is to simply slow the scan speed. The reduced number of scans per second helps to keep up with the screen refresh rate but diminishes the amount of touch data thereby creating jerky movements and jagged lines. Moreover, the effect is very pronounced on larger screens and even worse on the higher pixel density Ultra HD displays.

To remain competitive and to keep costs low, some touchscreen manufacturers are able to offer the degraded touch screen system today because many of the Ultra HD displays are only 30Hz, the HDMI 1.4 standard. But the latest Ultra HD displays are moving to the HDMI 2.0 display standard of 60 Hz so unless you have a touchscreen controller capable of maintaining a high scan rate for all touch points, the performance of the touchscreen will not meet customer expectations – it will exhibit jerky motion, cursor lag and jagged lines.

Touchscreen options for a Ultra HD displays

What is the best technology for a 4K display? Currently it would be a combination of technologies since at present, there is no one clear winner — each technology has limitations and may not be best suited for all applications. The perfect sensor would be fast, accurate, optically clear, scale easily without degradation of speed and performance, easy to integrate and be fully multi-touch capable. And, of course be cheap. While the perfect sensor has yet to be developed, there are viable technologies available and depending on the application you can find a technology that can probably get the job done.

The viable technologies available for large format touch include the following:

Optical – Optical is typically comprised of four cameras in the corner with a reflective strip around the edges. It is the fastest by far, it scales well and the cost is low but due to the limitation inherent in the technology, it is only possible to accurately track a few touch points. The rest are “best guesses” and depending on the firmware, sometimes the system gets confused and you end up with touch points in unintended places. The technology also realistically maxes out at about 70” since it requires line of sight to the edges and maintaining a very flat surface with a tolerance of +/-2 mm is impractical in the larger sizes above 70”. Optical is best for interactive white boarding where high resolution handwriting, single touch is required.

ProCap – Projected capacitive has until recently been cost prohibitive but the price is plummeting due to excess capacity from manufacturers chasing the handhelds and mobiles looking for new customers. However, large format Procap is expensive not only from a material cost but also from an integration perspective. Procap detects touch by emitting a capacitive field in front of the display which when you touch it, creates a distortion the electronics can track. The problem is that the larger the display, the bigger the field and manufacturers go to great lengths to mitigate the potential for interference. The electronics are significantly more complex since the amount of information needed to track touch points increases exponentially with size. Also important is that Procap requires a conductive coating on the glass. The most common is ITO, or indium tin oxide. Even though manufactures have become exceeding good at making the coatings as optically clear as possible, it still blocks out up to 20% of the light and creates a small distortion of the image which you can see at close range. ITO when viewed at an angle can also show a color shift towards yellow.

ITO Alternatives: Nano coatings and metal mesh are also being touted for large format as an alternative to ITO but there is an issue with the moiré affect which is the effect caused by interference of mesh pattern with display microstructure.   The bottom line is that while capacitive is a great technology for handhelds, it may not be for large format displays. It seems silly to put anything in front of the display that would degrade the image in any way. This is why edge based sensors are attractive.

Infra-Red: As edged based technology goes, IR is the most popular and probably has the largest install base IR. IR comes in a few flavors and there are a whole host of suppliers that seem to grow every month. Basically it is a grid of IR receivers and emitters that track the blockage of light caused by a touch point. The benefit is that it scales easily, can track many touch points and it is relatively inexpensive. But with most technology in the electronics industry, technology is driven to its lowest cost and so manufacturers have settled on a design that minimizes cost but does not necessarily bode well for Ultra HD displays. The issue has to do with scan speed. The bigger the display the more there is to scan. With data you need more sampling and processing which costs money and requires more power. The low cost design promoted by most suppliers uses USB power from the host PC. This is great since the touch screen can remain independent of the monitor’s power supply. USB from the host PC is fine for processing data for a 46” display but trying to crunch the data from a larger display requires more horsepower. To compensate for the increased data what some manufacturers have done is reduce the number of scan cycles at the expense of reduced resolution and accuracy. The problem is that the Ultra HD displays coming out are moving to a 60Hz standard and at that speed, the “dumb downed” IR sensors simply can’t keep up and there is pronounced cursor and touch point lag.

The best touchscreen technology for a 4K display

So of the viable large format touch technologies, what is the better touch solution? For all around price/performance it is probably IR. IR is edge based meaning no coatings or wires to degrade the image. It simply tracks multiple touch points, scales nicely and is easy to integrate while being low cost. But since the Ultra HD displays require greater speed and precision compared to a standard HD display, the IR system chosen would need to have ample horsepower for the larger sizes and is likely to require multiple processors and an external power source (other than USB) in order to provide an acceptable user experience.

Even after almost a decade of hardware improvements, the large format market is still just getting started and as Windows 8 continues to evolve and the interface matures, the adoption of large format touch screen will likely grow.   Ultra HD may be the kick start that’s needed to take the market from niche status to stellar market acceptance where software developers begin to focus on applications designed for large format touch. When that happens we expect to see increased demand for interactive, large format touch screens being the solution of choice for boardrooms, training rooms, command and control centers and anywhere visual data is shared with a group.

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