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Abstract
This demonstrates a wide color gamut and high brightness LCD TV using a conventional cold cathode fluorescent lamp (CCFL) backlight with five-primary (red, green, blue, yellow, and cyan) colors. Without changing the CCFL backlight and pixel size, the color gamut is widened from 72% to 90% and meanwhile the white brightness is increased by more than 20%, as compared to the three-primary.
I. INTRODUCTION
For most liquid crystal displays (LCDs), wide viewing angle, high contrast ratio, fast response time, high brightness, low power consumption, and wide color gamut are important metrics. The demand for a higher color gamut is ever increasing. Since the natural objects and cinema are significantly more colorful than the CRT TV standard, there is an urgent need to produce wider color gamut in order to reproduce the original colors with high fidelity. Using multi-primary colors to widen the color gamut has been demonstrated in projection displays and some direct-view LCDs. However, the display brightness is reduced and cost increased because of increased number of color pixels and fabrication complicities. So it is better to use five-primary technique that not only widens the color gamut but also increases the white brightness.
II. MULTI PRIMARY COLORS
Fig. 1. Color gamut triangles with a different green primary
We can use highly saturated RGB color filters to enlarge the color gamut. However, this method reduces display brightness dramatically because of the lower transmittance of each color. Thus, it is not a preferred approach from the energy saving viewpoint. Fig. 1 depicts the color gamut curvesof LCDs using two types of RGB primaries but at a different green primary. As shown by the dotted triangle, if we want to get good coverage of yellow then we cannot display a vivid cyan. On the contrary, if we shift the green point to cover more cyan, then we lose the fidelity of yellow, as the solid triangle shows. To overcome the limitation of RGB primaries, we propose here a five-primary LCD by including yellow and cyan color filters.
III. FIVE PRIMARY LCD TV
Five primary color LCDs are made by adding yellow and cyan color filters to the existing primary colors. This combination expands the color gamut, that can be rendered within the color spectrum that humans can discern with the unaided eye. Nearly all real surface colors can be rendered faithfully, including colors that have been difficult to render using conventional LCD monitors. In RGB we cannot get good coverage of yellow and cyan. But in RGBYC we will get a good coverage of yellow and cyan colors. So in RGBYC we will get more than 99% of real surface colors. The color gamut of conventional RGB LCD is ~76% NTSC. With the use of five primary color gamut increased to ~96%
In RGB color model we obtain cyan color by combining blue and green color filters. Similarly yellow by combining red and green color filters. But the colors thus formed will not be much saturated like the normal cyan and yellow colors. The spectrum of yellow CF covers a portion of red and part of green in order to get more saturated yellow than the combination of standard green and red color filters. Similarly the cyan CF covers a portion of green and blue to get highly saturated cyan color.
IV. CONCLUSIONS
The color gamut, brightness and power efficiency of LCDs were increased by the introduction of multi primary technology. Therefore three primary color LCDs are being replaced by the five primary LCDs, which produce wider color gamut in order to reproduce the original colors with high fidelity.