Comparisons

A comparison between the proposed method and other methods are shown in Table. 4. The two-color-field sequential method has some advantages such as color filter free (0), higher luminance and resolution (both 300%), lower field rate (120Hz), and less field number (2). Moreover, the experiment demonstrated the two-color-field sequential method which could also suppressed CBU effectively. However, the NCTU two-field method needs combined the locally controlled backlight system to display the color-mixing field images, which may increase the system complexity.

Table. 4 Comparison between NCTU two-color-field method and other FSC methods

Conventional RGB-field Philips two-field NCTU two-field

Luminance 100% 300% 150% 300%

Resolution 100% 300% 150% 300%

Color

breakup None High Medium Medium

Color filters 3 0 2 0

Color fields 1 3 2 2

Refresh rate 60Hz 180Hz 120Hz 120Hz

Light sources 1x CCFL 3x LED 3x LED 3x LED BL system Global Global Global Local control

5.5 Summary

Optimizations of the two-color-field method were done in this chapter. The colorimetric reproduction with optimal backlight parameters was acceptable with an average CIEDE2000 lower than 3 and average S-CIEDE2000 lower than 1. Moreover, the demonstrated result presented the two-color-field method could effectively reduce the CBU visibility. The third primary options can further to have another choice in the future work.

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Chapter 6

Conclusions and Future Works

6.1 Conclusions

FSC-LCDs do not need color filters and flash red, green, and blue images time sequentially to generate full color image by temporal color mixing. Therefore, FSC-LCDs have some advantages, such as high optical throughput and low material cost. However, the FSC methods are only with limited success because of the slow LC response time.

In order to overcome this issue, we proposed the two-color-field sequential method. The two-color-field sequential method for LCDs without color filter was proposed to further reduce field rate, so many commercial LC modes, such as MVA, TN, or IPS modes could be utilized. The results demonstrated that the average color difference, ΔE00ave, of the reproduced image was lower than 3 and average S-CIEDE2000 value, S-ΔE00ave was lower than 1. Moreover, the experimental results illustrated the proposed method also can suppress CBU visibility. Therefore, two-color-field sequential method is very promising for low power consumption large size LCD applications.

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6.2 Future works

The two-color-field sequential method was proposed to reduce the field number thus allowing sufficient time for LC response. The results demonstrated that the colorimetric reproductions were acceptable for human visual system. However, some specific cases showed that the colorimetric reproductions accuracy should be improved, as mentioned in section 5.3.

The algorithm of the proposed sequential method remains to be improved. For example, the third primary can be chosen based on the least significant image content, since less reproduction error is generated. Fig. 6-1 shows the simulation results of two-color-field method and improved algorithm. The third primary of reproduced image (Fig. 6-1(b)) was chosen based on the least image content, red. Compared the reproduction images with blue based (Fig. 6-1 (a)) and less component based (Fig. 6-1 (b)), the color difference percentage larger than 3 was reduced from 26% to 0%.

Moreover, the maximum color difference value was lower than 3 which is an acceptable color difference value for human visual system.

However, if there was a test image whose main image content had least color component, the optimal algorithm will sacrifice color information accuracy. Therefore, the analyses of content significance can further be localized in the future, which may result in different third primary at different areas. Finally, the option of third primary should be an important factor which can affect the colorimetric reproduction accuracy.

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S-CIEDE2000

min max std ave >3

0 2.6097 0.0228 0.043 0%

S-CIEDE2000

min max std ave >3

0 4.9483 0.1247 2.0844 25.8 %

(a) (b)

Fig. 6-1 (a) Reproduced image of the third primary is blue, and (b) reproduced image of the third primary with the least color component.

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Reference

[1] F. Yamada, H. Nakamura, Y. Sakaguchi, and Y. Taira, “Color Sequential LCD Based on OCB with an LED Backlight,” SID Symposium Digest Tech Papers, 31,

pp 1180-1183 (2000).

[2] N. Koma, T. Miyashita, T. Uchida, and N. Mitani, “Color Field Sequential LCD Using an OCB-TFT-LCD,” SID Symposium Digest Tech Papers, p-28, p.632-635 (2000).

[3] H. Yamakita, M. Sakai, Y. Taniguchi, J. Asayama, K. Adachi, “Field-Sequential Color LCD driven by Optimized Method for Color Breakup Reduction,” IDW’05, p.83-86 (2005).

[4] K. Sekiya, T. Miyashita, and T. Uchida, “A Simple and Practical Way to Cope With Color breakup on Field Sequential Color LCDs,” SID Symposium Digest Tech Papers, 3, p.1661-1664 (2006).

[5] T. Ishinabe, T. Miyashita, T. Uchida, K. Wako, K. Sekiya, and T. Kishimoto, “High Performance OCB-mode for Field Sequential Color LCDs,” SID Symposium Digest Tech Papers, 38, pp 987-990 (2007).

[6] K. Sekiya, T. Kishimoto, K. Wako, S. Nakano, H. Ishigami, K. Kaelaentaer, K.

Shimabukuro, D. Kunioka, T. Miyashita, and T. Uchida, “Spatio-Temporal

Scanning LED Backlight for Large Size Field Sequential Color LCD,” IDW’05, pp 1261-1264 (2005).

[7] http://product.it168.com/detail/doc/187572/detail.shtml

[8] C.-H. Chen, F.-C. Lin, Y.-T. Hsu, Y.-P. Huang, and H.-P. D. Shieh, “A Field

60

Sequential Color LCD Based on Color Fields Arrangement for Color Breakup and Flicker Reduction,” J. of Display Tech, 5(1), pp 34-39 (2009).

[9] F.-C Lin, Y.-P. Huang, C.-M. Wei, and H.-P. D. Shieh, “Color Breakup Suppression and Low Power Consumption by Stencil-FSC Method in Field-Sequential LCDs,” J. of SID, 17(3), pp 221-228 (2009).

[10] H. Nakamura, “A Model of Image Display in the Optimized Overdrive Method for Motion Picture Quality Improvements in Liquid Crystal Devices,” Jpn. J.

Appl. Phys. Vol. 40 (2001) pp. 6435–6440

[11] K. Kumagawa, A. Takimoto, and H. Wakemoto., “Fast Response OCB-LCD for TV Applications,” SID Symposium Digest Tech Papers, 48, pp 1288-1291 (2002).

[12] K. Nakao, S. Ishihara, Y. Tanaka, D. Suzuki, I. Satou, T. Uemura, K. Tsuda, N.

Kizu, and J. Kobayashi, “Response Time Improvement of OCB mode TFT-LCDs by using Capacitively Coupled Driving Method” IDW’00, pp 215-218 (2000).

[13] L. D. Silverstein, “STColor: Hybrid Spatial-Temporal Color Synthesis for Enhanced Display Image Quality” SID Symposium Digest Tech Papers,25, pp 1112-1115 (2005).

[14] E. H. A. Langendijk, “A novel spectrum-sequential display design with a wide color gamut and reduced color breakup,” J. of SID, 15, pp. 261-266 (2007).

[15] H. Seetzen, L. Whitehead, G. Ward, “A High Dynamic Range Display Using Low and High Resolution Modulators,” SID Symposium Digest Tech Papers, 34, pp.

1450-1453 (2003).

[16] H. Seetzen, W. Heidrich, W. Stuerzlinger, G. Ward, L. Whitehead, M.

Trentacoste, A. Ghosh, and A. Vorozcovs, “High Dynamic Range Display Systems,” ACM Transactions on Graphics, (2004).

61

[17] Y.-K. Cheng, Y.-P. Huang, and H.-P. D. Shieh, “Colorimetric Characterization of High Dynamic Range Liquid Crystal Displays and Its Application,” J. of Display Tech, 5(1), pp 40-45 (2009).

[18] F. Li, X. Feng, I. Sezan, and S. Daly, “Deriving LED Driving Signal for

Area-Adaptive LED Backlight in High Dynamic Range LCD Display,” SID Symp.

Digest Tech Papers, 38, pp. 1794-1797 (2007).

[19] D. Ellen, T. Lawrence, B. Roy, “Colorimetric Characterization of a

Computer-Controlled Liquid Crystal Display,” Color Research and Application, 29, pp. 365-373 (2004).

[20] M. R. Luo, G. Cui, and B. Rigg, “The Development of the CIE 2000

Colour-Difference Formula: CIEDE2000,” Color Research and Application, 26, pp. 340-350 (2001).

[21] X. Zhang and B. A. Wandell, “A Spatial Extension of CIELAB for Digital Color Image Reproduction,” SID Symp. Digest Tech Papers, 30, pp. 1-4 (1997).

[22] G. M. Johnson, M. D. Fairchild, “A Top Down Description of S-CIELAB and CIEDE2000,” Color Research and Application, 28, pp. 425-435 (2002).

[23] Y.-K. Cheng, Y.-P. Huang, and H.-P. D. Shieh, “Relative Contrast Sensitivity for Color Break-up Evaluation in Field-Sequential-Color LCDs” accepted by Journal of Display Tech., (2008).