The Curved Display Makes an Impression
Curved televisions, introduced last year, are entering the marketplace in greater numbers. These TVs offer viewers an enhanced immersive display experience compared to previous designs.
by Nam-Seok Roh
IN today’s marketplace, most monitors and televisions for sale use flat-panel displays (FPDs). Last year, the landscape of FPDs changed dramatically when the world’s first concave curved televisions were announced by several companies. However, most of these televisions were organic light-emitting-diode (OLED) based and much more expensive than conventional liquid-crystal-display (LCD) TVs. At IFA 2013, Samsung announced the world’s first ultra-high-definition (UHD) LCD-based curved television and began selling it in the first quarter of 2014. The curved-TV market is growing, and many television manufacturers are planning to sell curved TVs in the coming months and years.
Benefits of Curved Displays
Some critics have been skeptical of the benefits of curved TV, dismissing it as a marketing ploy. It is easy to see why people would come to this conclusion, especially since some aspects of a curved screen work against one of the main advantages of the FPD – its thin profile. A video currently on CNET1 lists five reasons not to buy curved TVs: (1) They are only a fad. (2) The price is too high. (3) The central viewing position is too narrow for groups of viewers. (4) The curved immersion effect works only in a very large (80 in. plus) form factor or if viewers are close up. (5) Curved TVs stick out from the wall.
These five criticisms are for the most part not valid: (1) For the following reasons and more, as explained in the rest of this article, curved TVs are not a marketing gimmick, although, admittedly, some people might choose to buy them because they are cool (Fig. 1). (2) The retail price for a curved model is just slightly higher than a comparable flat-panel TV; for example, the best models of Samsung’s curved UHD TV and Sony’s flat UHD TV are similarly priced at around $3,000. (3) The ideal viewing position is not as restricted as expected, which will be explained later in this article. (4) Smaller curved displays, for use in applications such as desktop monitors, are in development and are said to provide an effective immersive gaming environment. (5) The depth of a 55-in. curved TV is less than 4 in. (3 3/4 in. actually) and although it is a matter of personal preference, to most viewers these TVs look very nice when mounted on a wall.
Fig. 1: The world’s first curved UHD display from Samsung Electronics features an immersive viewing experience in a novel form factor.
Immersive Experience
The first thing noticed when watching a curved TV is that it feels very immersive. As shown in Fig. 2, we can calculate the extension of view by the curvature and width of the screen. In the case of a 55-in. curved TV, if the viewing distance, which is the radius of curvature, is 2.26 m, there will be a 0.7° extension of the field of view compared to a similar flat-TV experience.
Fig. 2: An extension of view is achieved by increasing curvature.
However, if the viewing distance, as well as the radius of curvature, is reduced to 0.61 m, the field of view increases by 24.6° compared to that of a comparable flat TV. Of course, this is an extreme example to illustrate this point because an actual curved television’s curvature would not be this pronounced. But nonetheless, a curved television does provide a larger field of view over an equivalent flat model, and the result is a more immersive viewing experience.2–5
Low Reflectance
Normally, in a home, windows or interior lighting will be reflected by the surface of the television screen. However, if the screen is curved, this reflected light will affect the television viewer to a lesser extent because the reflected light is spread out. As shown in Fig. 3, if the light source is constant, the unit area of reflection is larger in a curved screen, resulting in less reflected light being seen at any one specific location. For this reason, imagery in ambient light conditions should be much clearer in a curved display due to higher contrast levels on the curved unit compared to a similar flat-TV experience.
Fig. 3: Image-contrast degradation occurs with light reflection; there is reduced light reflection with a curved display.
Less Distortion
Returning to a consideration of the human-vision system, the eye is spherically shaped and the retina surface is curved. All the sensor cells reside in curved surfaces in the retina. As a result, some observed images might be distorted. For example, the Parthenon was constructed as a slightly curved structure (Fig. 4). If the columns had been straight and parallel, the beauty of the structure would not be the same. The situation is similar to that of television screens, especially large screens. Also, with television, theoretically, the distance from the eyes to the screen is different at every point, especially between the center and the edge of a flat screen, resulting in a de-focus of images. However, with a curved screen, the depth of focus remains constant on all surfaces if the screen is viewed at the focal point of the curvature.
Fig. 4: A flat image is “distorted” when viewed by a curved eyeball.
User-Performance Improvement
Another advantage of curved screens appears to be the speed at which observers can scan and analyze information. Tests performed by Shupp et al.6 showed an improvement in the information scanning speed in a curved display (Fig. 5). The researchers arranged 24 monitors in 3 × 8 tiled screens to make one large flat screen and also one large 760-mm-radius curved screen. The screen displayed satellite imagery on which users were given specific tasks to perform, one of which was a route-tracing task. Route tracing requires the user to traverse a limited and specific portion of the data without losing context. Users followed a given route across the displayed landscape, marking required features along the route while their performance was timed. The results showed that use of a curved screen improved user performance by about 20–25% over that of a flat screen. Part of the reason for this improvement was because the distance from a user’s eyes to the screen surface was much shorter in the case of a curved screen.
Fig. 5: Improved productivity for a curved display is shown with regard to “time to check route” in the map image. The task is 20–25% faster in the curved display because of less movement and faster scanning. Photo courtesy Shupp et al. (Ref.6).
Enhanced Side Readability
Today’s displays are normally wide format. We need to scan both the center and edge areas to gain all the necessary information. As shown in Fig. 6, the entire gap between detection times is smaller in the case of curved displays. This will help when users need to analyze large amounts of on-screen data, such as for the stock market or computer gaming.
Fig. 6: A curved display is more effective for users seeking information over a large area. Photo courtesy Shupp et al. (Ref. 6).
The Best Curvature
The current generation of curved televisions has a bending radius of around 4,000–6,000 mm. But, theoretically, the radius of curvature should be same as the distance between the viewer and the display so that the distance between the viewing point and every point of the display is the same distance. There will, therefore, be a consideration of what is the best distance, or best curvature, for the display. In other words, how do we know what the optimum value is for the radius of curvature? There are several definitions for the best distance to the display. For example, if we define the viewing angle as 30°, which is the range that the average human eye can scan left to right without any head movement, the best distance will be approximately 1.6 times the diagonal of the display. NHK defines the best distance based on the average preference of people who watch television; this distance is 3 times the height of the display. THX says a distance of 2.5 times the diagonal of display will create the optimal feeling of immersion for movies. In the case of a 55-in.-diagonal television, the best viewing distance will be between 2 and 4 m. This means the best radius of curvature will also be between 2 and 4 m.
Of course, this is just a theoretical definition; actual curvature is dependent on how a user watches television or from what distance. As noted above, Samsung Electronics has researched worldwide television watching distances and determined that 3–4 m is the normal distance for viewing large-sized televisions. And we concluded that at this distance, 4200 mm is the optimum curvature to maximize the experience. However, some viewers might sit as close as 2 m from the television, or even closer. For monitors, the distance is quite close, so more curvature would be needed for the best viewing experience. In the author’s opinion, the final product should have an adjustable curvature for various users’ viewing-distance choices. If curvature is adjustable, we can also change the television between single-user mode and multi-user mode in order to achieve the best viewing condition. Samsung (and LG) showed adjustable-curve TVs at the Consumer Electronics Show in January 2014.
Current Technical Limitations of Curved Displays
The first issue faced when making a curved LCD TV involves the stress created when the glass is made to curve. This stress will cause several problems, such as mechanical failure and optical distortion. Even a curved OLED TV has this problem if the curvature is large because current large-sized OLED TVs also use two layers of glass (one for encapsulation). Associated with this is the potential misalignment of the upper and lower layers of glass due to the curvature. For example, if a 55-in. television is curved to a radius of curvature of 4000 mm, there will be a maximum difference of a 25-µm misalignment between the two pieces of glass at a certain position of the screen. There will be color mixing at this point. Of course, most companies can solve this problem by putting the color-filter layer on the lower glass, which involves a technology called COA (CF on Array) or COT (CF on TFT) technology.
Also a challenge is that two sandwiched glass layers in a curved configuration will cause distortion in the cell gap of the liquid crystal, creating a decrease in brightness or black uniformity. LCD manufacturers are investing a great deal of effort to overcome these issues.
The Future of Curved Displays
As discussed in the previous section, the best curvature for a curved display might vary by viewing condition. As a result, there should be flat and curved transformable displays in real markets as shown in the CES 2014 demonstration. We also believe there is interest in curved monitors in the marketplace. We hope that in the near future not only television but also monitors will use the curved form factor. 2013 was the birth year of curved television products, and this innovation continued through 2014 and will continue to do so through 2015 and beyond.
References
1www.cnet.com/videos/reasons-not-to-buy-a-curved-tv/
2J. D. Prothero et al., Human Interface Technology Laboratory Tech. Rep. R-95-4.
3H. B. L. Duh et al., IEEE Proceedings, Virtual Reality (March 2001).
4M. Emoto et al., Presence, 2004, NHK.
5K. Masaoka et al., Proc. SPIE, Image Quality and System Performance II, 5688, 28.
6L. Shupp et al., Human–Computer Interaction, “Shaping the Display of the Future: The Effects of Display Size and Curvature on User Performance and Insights,” 24 (2009). •