Large-Area Displays Seen at SID 2006

Crisper video, sharper colors, and higher contrast were three of the major developments in large-area displays seen at SID 2006.

by Carl Cobb

THE 2006 SID Exhibition held in San Francisco showed what is new in large displays and in the innovative technologies that continue to improve performance, increase size, and lower costs. There were multiple TV-sized production liquid-crystal-display (LCD) units shown with sizes ranging up to 65 in. from Sharp, Toshiba, LG.Philips LCD, and Samsung SDI. In these ranges, the emphasis was not only on size, but enhanced performance in terms of improved motion blur, wider color gamut, higher dynamic range, and innovative capabilities such as 3-D. In addition to the production displays shown, larger-than-ever technology-demonstration models created buzz on the show floor.

Large Displays, Large Fabs

Samsung SDI showed the largest direct-view display at the conference, a 102-in. plasma-display panel (PDP) with a full high-definition (HD) 1920 x 1080 format and more than 1 billion colors (10 bits/primary). The full HD model, while a tad large for most homes, is targeted at the digital-signage and business markets. Samsung claimed specifications of a peak luminance of 1000 nits and a dark ambient contrast of 2000:1. Even on the bright exhibit floor, the contrast held up well and the brightness was enough to provide an excellent image with fine detail, saturated colors, and deep blacks.

LG.Philips LCD (LPL) had the distinction of having the largest LCD at SID 2006, a 100-in. HD display manufactured in LPL's Gen 7.5 fab (Fig. 1). The display had a 5-msec response time using the Super IPS (in-plane switching) mode and copper interconnect. Similar to the Samsung PDP, it also can display 1 billion colors. The massive display has a color gamut of 92% NTSC, plus a contrast ratio of 3000:1 due to the use of dynamic backlight control. The viewing is omni-directional because of the use of a combination of S-IPS and large-area compensation films.

Although the market for these ultra-large displays may be limited, the size of these one-per-motherglass displays serves to demonstrate the capability to produce large numbers of smaller panels on a single substrate. Samsung SDI can produce four PDP panels of the popular 50-in. size from a single motherglass at its Cheonan, Korea, fab; LPL can make 15 32-in. LCD panels from its fab at Paju, Korea.

 LG.Philips LCD

Fig. 1: LG.Philips LCD debuted its 100-in. HD LCD screen at SID 2006.

Since total capital costs per unit decline at approximately 30–40% for each LCD generation, the showing of these ultra-large show monitors is a signal not only of technical capability, but also of the ability to reduce manufacturing costs and thus continue the penetration of the television market by both LCDs and PDPs.

Crisp Video

Improving motion blur was one of the most active areas for LCD makers at SID 2006. Multiple solutions were demonstrated to avoid the motion blurring previously seen when LCD hold-type light valves began to replace the familiar "impulse" drive of cathode-ray tubes (CRTs). Overdrive drive schemes to improve LCD response time were evident in almost all video-oriented displays. In addition, myriad other approaches were demonstrated to improve video performance, either measured by moving-picture response time (MPRT) or gray-to-gray (GTG) transition times. Times quoted for displayed panels were often in the 5-msec range, a substantial improvement made in the past year.

One technique shown was a blinking backlight. Philips demonstrated its Aptura backlight line, which can support blinking by using hot-cathode fluorescent lamps (HCFL), emulating the CRTs impulse drive (Fig. 2). Two other methods demonstrated at SID 2006 were increased refresh rate with an interpolated image generated between each ordinary frame and black-level insertion between normal frames. Toshiba America Electronic Components, Inc., demonstrated an optically compensated bend (OCB) mode 32-in. display that was able to insert a black frame between each ordinary frame, effectively preventing any frame-to-frame image mixing (Fig. 3).

Philips

Fig. 2: Philips's Aptura backlight line can support blinking by using hot-cathode fluorescent lamps (HCFL), emulating the CRT's impulse drive.

 Toshiba

Fig. 3: Toshiba's 32-in. optically compensated bend (OCB) mode LCD inserts a black frame between each ordinary frame, effectively preventing any frame-to-frame image mixing.

More Colors

Wider-color-gamut displays, stimulated by the availability of backlights for LCDs powered by high-flux RGB light-emitting diodes (LEDs), were a big development at SID 2006. Compared to the standard 70–75% of NTSC offered by typical cold-cathode-fluorescent-lamp (CCFL) backlighting, LED backlights offered 100–105% of NTSC's gamut. Near its LED backlight unit, Samsung also showed a CCFL backlight with a 92% NTSC color gamut. An increased fluorescent color gamut was achieved by using a phosphor blend with a wider gamut than the familiar tri-band phosphor mix.

The approach using modified green and red phosphors seems to be similar to Sony's "WCG-CCFL" backlighting used in some models of Sony Bravia televisions and was discussed by Takahiro Igarashi in a poster paper at EuroDisplay 2005 (Igarashi, et al., page 7). The paper also reported a 92% NTSC color gamut and discussed limitations in the standard color filters with regard to rendering saturated blue colors. (Marketing literature for Bravia says that both the phosphor and the color filters were optimized for product release.)

Further extensions in color gamut were on display by Genoa Color Technologies, which offered display designs with expanded color gamut using four and five primaries (RGB plus yellow and cyan). In private showings, Novalux demonstrated a prototype rear-projection television (RPTV) with three primary lasers for backlighting, further expanding the color gamut.

As the color gamut expands beyond the NTSC standard, expanded color-management software is necessary if colors are to appear realistic. In the technical sessions, representatives from Mitsubishi Electric Corp. discussed expanded color spaces for its six-LED display (paper 19.1, Sugiura, et al.) and a laser-backlight projection TV (not shown) that achieves 190% of BT-709, the color space used for HDTV, or about 123% of the area of the NTSC color space. With new backlighting options, and in an environment of six-color photo printers, expect color to remain an active topic. (Editor's Note: Information Display will explore this issue in-depth in a two-part series beginning in the September issue.)

Higher Contrast

The flexibility of LED backlighting was showcased with high-dynamic-range (HDR) LCDs. By separately modulating both the local brightness of the LEDs in the cavity backlight and the LCD transmission, BrightSide Technologies, Inc., was able to achieve an astounding 200,000:1 contrast ratio when viewed in a dark environment. Images shown at the exhibit had excellent detail in both bright and dark areas, using the backlight to set the local luminance and adjusting the LCD in that area to a finer scale than would have otherwise been possible. The combination achieves a 16-bit dynamic range in a single image (Fig. 4).

The less-complicated approach of modulating the overall brightness of the backlight, applicable to fluorescent as well as LED backlights, was in evidence in many TV-oriented large displays, producing sequential contrasts of 2000:1 or more. ASTRI (Hong Kong Applied Science and Technology Research Institute) also demonstrated an alternate method of modulating LEDs and the LCD to achieve high dynamic range.

Color without Filters

One innovative use of a combination of an LED backlight and a fast-switching OCB mode LCD was Samsung's demonstration of a prototype 32-in. display without any color filters. A color field-sequential approach – similar in concept to the method used with Texas Instruments' DLP projector engines – rapidly displays monochromatic RGB fields in sequence. When an LED primary is active, the light is available for transmission, avoiding the ~70% loss from absorptive color filters. As with earlier DLP projectors, color breakup is sometimes visible in fast-moving images and flicker is noticeable. A 180-Hz frame-sequential rate (60 Hz each for R, G, and B) allows noticeable flicker, particularly in the case of single-color scenes. Additional improvements in refresh rate may be necessary to fully compete with standard LCDs that use color filters. However, the potential backlight power and cost savings suggest a promising technology for development.

Toshiba also showed a 9-in. display from Toshiba Matsushita Display (TMD) using field-sequential color. Intended for auto-motive navigation, it can display both high brightness and high resolution. A bonus is the fast low-temperature performance available with OCB mode.

BrightSide Technologies

Fig. 4: These three images represent the capabilities of BrightSide's High Dynamic Range (HDR) technology. In order to see the full detail of this high-dynamic-range image on a conventional display, it is necessary to show three different versions of the same image. Different exposure settings help show off the different brightness levels of separate elements of the same image. BrightSide's HDR allows each of the distinct elements of this image to be displayed in full vitality in a single frame, eliminating the need for "tone mapping."

3-D Technologies

Another active area for extension of technology was in 3-D displays. The most arresting display was the Philips WOW displays and the associated software and real time 3-D rendering for 2-D broadcast content (the winner of the 2005 SID/Information DisplayDisplay of the Year Gold Award). For more on this display, see "Novel Displays Seen at SID 2006" beginning on page 28 of this issue.

ColorLink showed a number of 3-D applications based on passive polarized glasses. Direct-view LCDs used ColorLink's X-pol micropolarizers integrated into a single display panel. In addition to its existing 17-in. product, Colorlink showed 20.1- and 42-in. prototypes. These single monitors divide pixels into left- and right-eye fields, halving the horizontal resolution. A full-resolution projection system was also demonstrated, where a high-frame-rate projector alternated left and right fields while a ColorLink switchable retarder plate in the projector modulated the projector polarization to match left- and right-eye passive eyeglass polarizers (Fig. 5).

Backlighting and Light Management

With the continued productivity gains in LC cell production and consequent reduced costs, the backlight has emerged as a major cost factor for TVs, which require luminance levels of 500 nits or more. Alternatives for reducing costs divide into more-efficient light generation and better light usage.

For more cost-effective light generation, Philips offers HCFL bulbs, and development continues with flat fluorescent backlights. External electrode fluorescent lamps (EEFL) enable parallel driving, reducing the number of inverters required. For the present, CCFL designs continue to dominate production and are decreasing in cost as volume ramps.

Managing the generated light more efficiently is the other option for reducing the cost of a display's backlight. 3M has long dominated light management with its brightness-enhancement film (BEF) and polarization recycling films (DBEF). 3M had a very effective demonstration of the cell temperature of LCD-TV units. With the same brightness, the 3M equipped TV cell was 10° cooler than the TV with no films but a brighter backlight. The 3M DBEF films perform polarization conversion, resulting in an increased panel luminance of about 56% for a given backlight input. The 3M demonstration showed that the same polarization conversion technology could achieve comparable panel luminance with a reduction in backlight power by about 34%. Since the temperature also alters LCD performance, there are multiple reasons for efficient light management.

Alternative BEF films were shown by Eastman Kodak and GE Plastics as they contend for a share of the growing LCD films market. Kodak announced a microlens film in two thickness grades based on a monolithic polycarbonate structure. Polycarbonate is a higher-refractive-index material than acrylic, the resin used in 3M's BEF-II and BEF-III products. The higher index of polycarbonate boosts the luminance by about 75% on axis, according to Kodak's published specifications. Kodak's products also employ a random microlens spacing to reduce moiré. GE Plastics announced an extension to its Illuminex product line, adding a prism film based on Lexan, GE's polycarbonate brand.

As LED backlights begin penetration into larger displays, brightness-enhancement films will be an important element in the design of cost-effective backlight subsystems. LED designs now cost more, per lumen generated, than CCFL designs. Brightness enhancement is therefore more cost effective when replacing LEDs than when replacing CCFLs; this will tend to increase the adoption in LED designs. Conversely, as CCFL backlights or alternatives such as EEFL become less expensive, the substitution value of brightness-enhancement films becomes less.

In the PDP area, Fuji Photo Film Co. announced Shield Rex, a silver EMI shielding film targeted to replace copper films that currently have the dominant share.

Summary

With both LCD and PDP revenues reaching new records, 2005 was an excellent business year for large-area displays. The technology showcased at SID 2006 indicates that the pace of innovation continues. Developments in better-looking displays are apparent. Continued design improvements and resulting cost reductions, along with this improved viewing, will continue to support adoption of flat panels. •

 ColorLink

Fig. 5: ColorLink showed 3-D displays requiring passive polarized glasses in both projection and direct-view LCD (right) applications.