The Quality of Your Display Shouldn’t Be a Matter of Perspective

Fri, May 19, 2017
Shaina Warner  | 
Display quality has never been more valued than it is today – and not just because we want the ultimate HDTV experience or the prestige that comes with owning the latest OLED smartphone (although these are definitely factors). The crux of the matter is that displays are more critical to device function and control than ever before. Think about it – how many analog components have been replaced by displays in this year’s vehicles? Beyond GPS panels, displays now function as consoles for all vehicle controls, including navigation, entertainment, heating and air conditioning, and even dashboard indicators and gauges. This trend continues in appliances, aerospace, commercial buildings, manufacturing spaces, and beyond. Displays are everywhere, and they are becoming central to the way we accomplish everyday tasks.
Although displays have improved the ease with which we interface with devices, the proliferation of displays into all areas of life provides a unique challenge. We are no longer tethered to stationary displays, viewing them only when we are facing televisions and computer screens, perfectly perpendicular, sitting relatively motionless at our couches or desks. Displays are now appearing everywhere – from our cars to our smartphones – and can be taken anywhere – even worn, like smart watches, virtual reality headsets, and other wearables. Despite this, we still fully expect to be able to use our display devices seamlessly, regardless of the viewing environment – because, simply, we have to be able to use our displays in order to operate our devices. Just imagine how much more important this is in fields like automotive, aerospace, defense, and other regulated industries – human welfare and even national security may now rely on the ability to clearly visualize information on displays.
High-value consumer electronics come with high quality expectations for displays, no matter how the user views it.

Some displays have more important roles than others. The visual quality of displays integrated into vehicles and aircraft must be consistent regardless of position, and even operator height.

This is how “view angle” has come to be such an important factor in display design and evaluation. We can’t assume, just because a display appears to be free from visible defects from a given vantage point, that it exhibits the same level of visual quality across the spectrum of possible view angles. Display position relative to the user is unpredictable – this is something the manufacturer can’t control. So, the manufacturer must ensure quality regardless of position. To achieve this, manufacturers are adding an additional step to their quality control operations: measure every angle at which a display may possibly be viewed to guarantee visual quality at every angle.
The three most important things to measure to determine display view angle performance are:

  • Luminance: Brightness should be uniform regardless of viewing position to ensure contrast of digital elements and visibility in any lighting condition.
  • Chromaticity: Colors should appear the same regardless of viewing position to ensure quality (for example, “red” viewed at a 0° angle should not appear purple at a 60° angle).
  • Contrast: Angular contrast (brightness and color) should be sufficient at every view angle to ensure the legibility of symbols and text against a background.
Every type of display technology behaves differently when viewed at an angle. For instance, because they rely on backlight units (BLUs) for illumination, LCDs are particularly bright when viewed straight-on, but lose their brightness when viewed at increasing angles.

The LCD display at left exhibits inconsistent brightness; light is affected by passing through several layers of the assembly from the backlight unit (BLU). OLED displays, like the one at right, emit light organically and have fewer issues with brightness consistency across view angles.

OLED displays, on the other hand, have an emissive light-producing layer, which results in fewer issues with brightness consistency when viewed at an angle. However, color consistency may vary – not only from angle to angle. OLED devices from the same manufacturer can actually exhibit different patterns of inconsistency from device to device (that is, the light and color of each device may vary at different degrees of severity when viewed across angles). This is especially poignant now that most major smart device manufacturers are turning to OLED as the display technology of choice, and high consumer expectations dictate that all devices of a given model exhibit the same level of quality from device to device.

Here we see the results of conoscopic view angle chromaticity measurements for three OLED devices, all produced by the same manufacturer.

Getting a handle on view angle performance during display design is one part of the solution. But controls must be extended to production lines to ensure that absolutely no variability is caused by manufacturing processes, such stress on materials during assembly, or new, slightly different supplier stock entering the line. As innately variable as display technologies already are, there is no room for adding extra inconsistency when operations move to mass production on the line.

During assembly, display quality can be affected by several factors: defects within component layers, light leakage around layers, pressure applied during enclosure, or stress applied to the display module.

What are the hallmarks of a production-level view angle measurement system? Well, they are the same as any piece of production line equipment.
Production-level equipment should be:
  • Automated
  • Accurate
  • Fast
  • Repeatable
  • Compact
  • Easy to integrate
  • Easy to use
  • Low-cost

Current production-level display test solutions for view angle measurement offer combinations of these characteristics to various degrees of proficiency. Since view angle performance evaluation requires multiple measurements, achieving high levels of accuracy usually means increased cost and complexity. This is because multiple high-caliber parts are needed to move around a display to measure each view angle. (This is seen both in goniometric solutions where camera or display are rotated in relation to one another, and in integrations where robotic arms are used to position a camera at various angles above a display). Sacrifices to repeatability are also made every time you employ moving parts, since any unexpected movement may cause inconsistent imaging. In more compact solutions, alternative lens options are used to reduce integration size and offer a completely turnkey, cost-efficient solution. Cameras that employ optics such as a fisheye lens can capture a complete arc of view angles in a single measurement for evaluation, but the image processing required to remap the captured fisheye image at the appropriate proportions can result in decreased measurement accuracy.
View angle measurement solutions including a goniometric system, robotic arm solution, and a fisheye lens.

An elegant marriage of the above list of production equipment characteristics demands a solution that does not distort image quality, does not require excessive equipment or moving parts, and is able to measure all view angles at once to a degree of accuracy and repeatability necessary for display quality operations. This solution is a conoscope lens – so-called because it can capture a full “cone” of angular light in a single measurement. The secret sauce to this technology is Fourier optics, which receive angular distributions of light and convert these into parallel emissions that map onto the attached camera’s CCD. The result is a high-quality image that enables quick view angle performance evaluation from a simple, integrated solution.

A representation of the visible “cone” of angular light emitted from a single spot on a display.

A conoscope lens attaches to a CCD camera to measure a full cone of angular light at once.

Fourier optics map a light-emitting spot to a CCD in such a way that each pixel corresponds to a different emission angle.

Radiant Vision Systems recently introduced a conoscope lens to its portfolio, which mounts directly to our existing line of ProMetric® Imaging Colorimeters and Photometers. Compared to competitive solutions, Radiant’s conoscope lens provides the necessary form factor, scope, speed, and accuracy for evaluating view angle performance for displays in both R&D and production environments. In fact, the same conoscope solution can be implemented in both the design and quality control phases of device manufacture, ensuring absolute consistency of measurement data from start to finish, while taking advantage of a single software environment for increased efficiency. The Radiant conoscope is extremely cost-efficient, thanks to limited equipment needs and its competitive price point as an optical accessory, compared to multi-part system solutions.

Radiant’s new conoscope lens is a fast, accurate, low-cost view angle performance solution for use in R&D and production lines.

Since the new conoscope lens attaches to Radiant’s existing line of ProMetric cameras, it is also able to provide accurate photopic measurements to 16-megapixel resolution using the high-resolution CCDs of the ProMetric Y16 and ProMetric I16 imagers. Additionally, the ProMetric cameras feature tristimulus optics that correlate to human visual perception of light and color, ensuring the truest assessment of display and view angle quality possible – quality as the user perceives it.
Although view angle is no longer a constant for display devices, your display quality shouldn’t be a matter of perspective. The most highly-rated displays will offer quality across the board (or across all angles), and extending view angle performance evaluation to the production line will ensure that this level of quality is achievable. Choosing a view angle measurement solution should ultimately take into account advantages in speed, accuracy, cost, and integration simplicity offered by each technology. While Radiant’s conoscope lens isn’t the only solution for view angle measurement, it does offer an elegant combination of production-level advantages, as well as Radiant’s expertise as a leading provider of display test solutions for over 25 years.
Of course, the best way to learn the advantages of the conoscope lens is to see them for yourself. Radiant Vision Systems Product Marketing Manager, Bo Magluyan, recently presented a webinar introducing this latest addition to the Radiant ProMetric camera suite.

See a demonstration of the conoscope lens in “Evaluating Viewing Angle Performance Using Radiant’s Conoscope Lens”:
  • Fast, accurate, low-cost view angle measurement solution
  • Address complex view angle challenges such as OLED color consistency and defects in embedded displays
  • Reduce the cost and complexity of equipment with a single, compact camera system
  • Use the same measurement system from R&D to in-line quality control, with ability to acquire additional measurements by switching camera lenses