Each year, the Journal of the Society for Information Display (JSID) recognizes a published student paper on the basis of originality, significance of results, organization, and clarity. The 2009 award goes to "Color-Breakup Suppression and Low-Power Consumption by Using the Stencil-FSC method in Field-sequential LCDs" by Fang-Cheng Lin, Assistant Professor Yi-Pai Huang, Ching-Ming Wei, and Professor Han-Ping D. Shieh of National Chiao Tung University (NCTU) in Hsinchu, Taiwan.
Now that LCDs have reached a certain maturity and dominance in the marketplace, most research efforts are aimed at refining rather than redefining them, and, in particular, at creating LCDs that use less power. The authors' award-winning paper focuses on creating a new method for frame-sequential color (FSC) on an LCD by applying a technique they call the "stencil" method.
Field-sequential color is a well-understood process for making full-color images by sequentially flashing the red, green, and blue fields quickly enough so that they merge together when observed. In the case of single-panel DLP projection and other types of systems, a very high field rate on the order of 540 Hz is used to prevent the undesirable phenomenon of color breakup (CBU) – basically, the primary-color fields being individually observable by the user of the display. For large-area LCD panels, high field rates are not achievable, so the authors have proposed the use of their stencil field-sequential-color (Stencil-FSC) method, which incorporates local color-backlight-dimming technology at a much lower field rate of 240 Hz, which they report significantly reduces CBU effects.
This methodology is applied to a high-resolution large-area AMLCD without color filters. Color filters cut the light emission of an LCD panel by a factor of three because each color filter for a primary color absorbs the light of the other two primary colors. Because FSC allows the color filters to be eliminated, the luminous efficacy of the LCD can theoretically increase by as much as three times.
The authors propose the insertion of a fourth field in the normal three-field sequence of the FSC process. This fourth field is a full spatial but low-color-resolution sub-frame that can be achieved by properly addressing the full-color two-dimensional dimming backlight. By using the first sub-frame to show a multi-color image with high luminance and rough color content, the luminance of the other three primary-color images was greatly reduced, making CBU almost imperceptible. The first sub-frame would be compiled by a low-resolution color image utilizing a locally controlled RGB-LED backlight and a high-resolution LC image. Therefore, the Stencil-FSC method not only reduced CBU, but also increased dynamic contrast and lowered power consumption.
"Field-sequential color is one of the major ways that future LCDs can cut power consumption, but the CBU problem has stalled its adoption," says Larry Weber, a member of the review panel that chose the winning paper. "The stencil method could be the needed breakthrough."
To prove the theory, the Stencil-FSC method was implemented on a 32-in. FSC-LCD TV that yielded a dynamic contrast of 27,050:1, with an average power consumption of less than 40 W, a color gamut of 114% NTSC, and imperceptible CBU. The authors propose that this low-power FSC-LCD TV without CBU holds promise for the next-generation of "green" LCD-TV applications.
— Information Display Staff