In the present day, flexible displays are a key headline in consumer electronics news.
The most renowned manufacturers of smartphones, TVs, tablets, and more are utilizing the flexibility of emissive (no backlight necessary) display technologies such as microLED, OLED, and others in order to advance the design of rigid, flat panels.
Samsung invited its consumers this month to “reshape their future” with the launch of its latest Samsung Galaxy Fold smartphone, showcasing a foldable AMOLED display screen that opens outward to unfold a display that is tablet-sized, and inward to reduce the display down to pocket size.
Alternative foldable and flexible designs are increasingly popular, filling booths at all global consumer electronics and display trade shows from CES in January, to Display Week in May to August’s Touch Taiwan.
Applications vary from the most popular trend, that is flexible tablet and smartphone displays, to more creative ideas such as curved displays on vases, flexible displays on textiles, and bespoke displays on three-dimensional packaging.
A look at the range of curved display concepts by Visionox booth at this year’s Display Week 2019 in San Jose, CA. (Video Source: Dave Haynes, sixteen-nine)
Automotive human-machine interface (HMI) innovation often reflects the technical accomplishments and demands of the consumer electronics market, without the majority of the wild concepts.
The desirability of the automotive space is that there are plenty of practical applications for displays in which the advantages can be instantly realized.
Displays may be the best HMI to replace the excess of analog components (knobs, gauges, buttons) within the vehicle for example.
Conventional rectangular and even flat-panel freeform displays reduce the extent to which displays can be integrated into the design of the vehicle.
As automakers cannot recreate the whole vehicle to adapt to the display, they need the display to reflect the shapes of the vehicle’s interior to optimize reliability and driver comfort.
Flexible display technology is now offering the ability to adapt to the dimensionality of the interior of the vehicle which may result in an automotive display boom.
Many intriguing concepts have been presented by display makers, such as these future displays below rendered by Flexenable.
Flexible display concepts that match the dimensionality of the A-pillar (left) and door frame (right) to enable seamless, space-saving integration that enhances visibility and operability. (Source: Flexenable)
A possible target for one of the first curved display integration designs is in direct view of the driver.
Displays that are situated on the center stack of the vehicle or the speedometer region are becoming more popular. These are utilized to display important information to the driver for monitoring the performance of the vehicle, and tracking navigation, speed, and distance.
These displays significantly enhance the accessibility of instant and complex data compared to their analog counterparts.
They have the additional advantages of greater brightness, contrast, and color for easier visibility in different lighting conditions.
Curved displays have already entered production applications in order to be integrated into automotive dashboards.
The video displayed below is from Continental Automotive Group regarding the transformation of the cockpit from analog to digital. It also describes how the 3D display molding system for their curved displays utilizing plastic materials has been optimized.
3D curved display surface for premium car dashboard
(Source: Continental Automotive Global)
An additional production application shown below is being called the ‘world’s first curved instrument cluster on the road.’ Bosch designed this small curved display to precisely fit into the speedometer section of the latest digital cockpit for the 2019 Volkswagen Touareg.
A curved instrument panel display by Bosch manufactured for the 2019 Volkswagen Touareg, shown inside (left) and outside the vehicle (right). (Source: Bosch)
The Bosch display panel has a 12.3 inch diagonal size with a 1500 millimeter radius of curvature (also referred to as 1500R in the world of curved displays).
This horizontal curve is designed to benefit the user in both matching the dashboard’s shape, but also in elevating the vehicle’s sense of luxury. At the same time, it provides extraordinary visualization advantages for the driver.
Studies on the visualization of curved monitors compared to flat monitors have proposed that curved displays can decrease visual fatigue in the user, and can enhance the comfort of the viewer.
Haeng Jin Lee and Seong Joon Kim describe the influence of display curvature (1000R, 2000R, 3000R, and 4000R) on twenty adults who carried out a range of visual tasks employing each display. This study is described in their paper ‘Factors Associated with Visual Fatigue from Curved Monitor Use: A Prospective Study of Health Subjects’.
The participants’ subjective symptoms and their eye movements were analyzed during the study. The conclusive finding was that ‘eye pain’ (visual fatigue) was much stronger for users who had viewed a flat monitor rather than a monitor with a 1000R curvature.1
An illustration of display curvatures as seen at a specific distance by a human viewer. (Source: Viewsonic)
This investigation verifies the general consensus of panel makers who believe that curved displays enhance visualization due to the radius of human peripheral vision closely matching a curvature of 1000R.2
A horizontal curvature of 1000R can decrease eye movement and the deformation of elements at the edges of the display. It can also maximize visual immersion, all of which are very critical for drivers, who all have a highly restricted amount of time to comprehend display information when operating a vehicle.
An illustration of the typical human field of vision and extended peripheral vision compared to a display with 1000R horizontal curvature.
An illustration of how curved displays reduce visual distortion at the display edges when seen from a single point (i.e., the viewer’s location). (Source: Viewsonic)
These advantages give automakers a solid foundation for the pursuit of curved displays, if an attractive aesthetic and design freedom were not enough.
Now that displays are taking new shapes, the last question is how to keep objective quality standards for visual display performance in their various forms.
Quantitative measurements are required to make sure that the quality of curved displays meet all the same visual performance standards as conventional displays, both in terms of user expectations and vehicle functionality.
As many manufacturers know, the automation of the process of measurement along a curve continues to be complex for any vehicle display or surface.
Flat panel displays (FPDs) have been the foundation of display test techniques for years.
Display measurement tools, for example photometric imaging systems are created to record contrast, uniformity, luminance, and other data in one image over a flat, two-dimensional plane, suiting the dimensionality of conventional FPDs.
These displays are essentially measured from one perpendicular angle to reduce variations in focus or view-angle influences, such as changes to color, contrast, or brightness that may shield defects when light is received at an angle through the different display layers.
Measuring curved displays demands an updated approach to account for differences along the curve.
A conventional analysis technique, a single perpendicular measurement angle, and a single measurement image may not be adequate to ensure the precision of the data utilized for the evaluation of curved displays.
The size, contrast, and shape of image defects, for example, may seem to change according to how far the imaging system deviates from a perpendicular position (a ‘normal’ position corresponding to the surface of the display).
Defects on the display edges may fall out of focus or be distorted when the imaging system is aligned to a central point on a curved display.
These pixel defects displayed below (cropped from a measurement image captured by an imaging photometer aligned to a curved display’s center) differ dramatically regarding contrast and shape from the center to the display’s edge.
If someone was looking for tiny defects similar to these in order to qualify a curved display, it is likely that thresholds would be set for the estimated eccentricity or contrast (how far from ‘round’ the defect shape is) of a pixel defect.
The parameters for detection may not distinguish the pixel defect on the edge as it does not match the predicted features of a pixel defect.
This could mean that defects escape the visual display assessment because of the weaknesses of the conventional measurement technique.
Comparison of pixel defects in a measurement image of a curved display, captured by an imaging system positioned perpendicular to the display center. From this angle, a pixel defect at the center of the display (left) appears more high contrast and round than the defect at the edge (right).
Formats for displays are changing, and measurement techniques must keep up. The engineers at Radiant have carried out a series of laboratory-based investigations to study the accuracy of measurement techniques and imaging system specifications for qualifying curved displays.
The positive news is that there are methods to decrease the effects similar to those seen in the pixel defect differences outlined above.
High-resolution imaging combined with a large depth of field (DOF) established on lens aperture settings, and inventive combinations of analysis techniques and imaging system positions can develop a highly efficient and effective curved display measurement solution that needs minimal corrections to conventional display test techniques.
Enhancing the resolution of an image-based measurement process introduces photo-sensing elements (sensor pixels) to the measurement system, which allows the process to record more intricate details, such as the more precise changes of light, within smaller spatial display areas.
Measurement images showing how detail in display pixels increases (in this case, illuminated pixels) as the resolution of the imaging system is increased (lower resolution image at left, higher resolution at right).
Increasing the resolution expands the number of sensor pixels employed to discern a defect at the display-pixel level.
When a defect is recorded utilizing additional sensor pixels, the tolerances utilized to discover defects can be made much more accurate, reducing the chances of false defects being detected (such as particles on the display that appear the same as pixel defects) and allowing the system to distinguish all defects of a particular size.
The increase of DOF (through the restriction of the aperture or F-stop of the imaging system lens) can enhance the range of distances at which elements can be imaged in sharp focus.
An illustration of the impact of DOF when capturing images at a given focus distance. (Source: PhotographyLife)
As described in this article, defects are difficult to notice across curved displays as they can fall out of focus in images recorded from only one position.
This is due to the imaging system not being able to record all areas of the display at a ‘normal’ (perpendicular) angle just one image.
One possible answer is to take several images across the curve of the display for evaluation. This increases the amount of visual performance data gathered at all display areas and also reduces view-angle effects and focus changes that decrease the contrast and clarity of defects positioned along the curve.
This multi-image technique could significantly enhance defect detection repeatability and accuracy for the measurement of curved displays.
An illustration of a multi-image measurement method that rotates the imaging system to several points across the curve of the display to capture defects in each region at a more “normal” angle.
Produced from materials originally authored by Shaina Warner from Radiant Vision Systems.
This information has been sourced, reviewed and adapted from materials provided by Radiant Vision Systems.
For more information on this source, please visit Radiant Vision Systems.
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