Chapter 5 Optimization of Color Breakup Suppression
5.4 Discussions
By optimization works presented in the last sections, optimized hardware parameters in Stencil-FSC method were gathered. Number of backlight divisions is 24*24, light spread function is related to Gaussian low-pass filter with D0 equal to 0.01, and dimming ratio in backlight colorful method is 10%. These optimized parameters will achieve better CBU suppression compared to the demonstration mentioned in chapter 4. Now, a quantification discussion will be made about CBU caused by conventional RGB color sequence and Stencil-FSC method with optimized parameters, and the results are shown in Fig. 5-12 and Fig. 5-13. In Fig. 5-12, theΔE values of CBU caused by RGB color sequence and Stencil-FSC method are presented.
In the following, an index, CBU suppression, is defined to evaluate how many percentage of CBU caused by RGB color sequence is suppressed. The equation is presented in Eq. 5-4, and the results are shown in Fig. 5-13
%
×100
⎟⎟⎠
⎜⎜ ⎞
⎝
⎛ −
= −
RGB
FSC Stencil RGB
CBU CBU n CBU
Suppressio
CBU (5-4)
According to the results, Stencil-FSC method can suppress 41%~98% CBU compared to that of RGB color sequence in the nine test images, and the average CBU suppression is equal to 62%. Therefore, Stencil-FSC method with optimized parameters can solve the CBU issue successfully on an FSC-LCD.
0
Aborigine Bird Lotus Basketball Butterfly Azalea Mountain Church Coast
CB U_ Δ E (10^ 6)
RGB Stencil‐FSC
Test images
Fig. 5-12 ΔE of CBU caused by RGB color sequence (blue bars) and ΔE of CBU caused by Stencil-FSC method with optimized parameters (red bars).
41
Aborigine Bird Lotus Basketball Butterfly Azalea Mountain Church Coast
CBU Suppression (%)
Test imgaes
Fig. 5-13 CBU suppression of nine test images
5.5 Summary
Optimization works of Stencil-FSC method have been done in the chapter for achieving best CBU suppression. Nine test images were chosen by two indexes, detail complexity and color complexity, in order to gather general and reliable results. The optimized results of hardware parameters: number of backlight divisions is 24*24, light spread function which related to Gaussian low-pass filter with D0 is equal to 0.01, and dimming ratio in backlight colorful method is 10%. The optimizations can be recommendation parameters for FSC-LCD in the future. By utilizing the optimized parameters, Stencil-FSC method can suppress 62% CBU caused by conventional RGB color sequence on average.
Chapter 6 Conclusions and Future work
6.1 Conclusions
An LCD using field sequential color (FSC) technique displays field images in time sequence and generates full-color images using the temporal color mixing method. By using the FSC technique, the LCD does not need color filters (CFs) and is based on a LED backlight system, the FSC-LCD has several attractive advantages, including higher light efficiency/lower power consumption, easier manufacturing of higher image resolution, higher color saturation, and CFs cost saving. Therefore, the FSC-LCD has high potential as commercial applications in display market. However, FSC face a serious issue; color breakup (CBU), when there is a relative velocity between the viewers’ eye and observed images. The CBU will degrade image quality and cause viewers discomfort. In recent years, although many methods have been proposed to suppress CBU, they may be not only limited by LC response time but also cause image distortion. Thus, CBU is not suppressed effectively. Thus, the FSC-LCD has not been widely utilized in display applications yet.
In this thesis, we proposed the “Stencil Field Sequential Color (Stencil-FSC) method” with four fields to suppress the CBU phenomenon in the FSC-LCD. A rough multi-color image is displayed in the first field instead of conventional single-color fields, and the following red, green, and blue fields are only utilized to correct color detail. By using the Stencil-FSC method, the color and luminance of red, green, and blue fields can be much reduced, so it is helpful for suppressing CBU effectively.
Moreover, two optimized algorithms, backlight colorful method and Fourier transformation process, were proposed to get much better CBU suppression and reduce computation complexity in hardware, respectively. Two experimental demonstrations have presented and verified the CBU suppression of the Stencil-FSC method. Moreover, the experimental demonstration on the 180Hz field rate, 32”
FSC-LCD supported by C-company achieved attractive performance, including average power consumption of 44W (conventional CCFL-LCD:105W), wide color gamut (114% NTSC), and a high Contrast ratio(27000:1) in high contrast image.
Finally, optimizations of hardware parameters have been done to get the best CBU suppression. When number of backlight division is equal to 24*24, parameter D0 of Gaussian low-pass filter in Fourier transformation process equals 0.01, and dimming ratio is 10% using backlight colorful method, the Stencil-FSC method can have optimized performance. Those parameters can be recommended parameters for FSC-LCD producer in the future. Furthermore, the Stencil-FSC with optimized parameters can suppress more than 62% CBU caused by conventional RGB color sequence.
In recent decades, the energy prices have been rising, and the demand for power saving technology is more and more important. Thus, the Stencil-FSC method is based on the concept of green technique, and it may make an FSC-LCD have high potential to be a next generation display technology with high image quality and ultra-low power consumption.
6.2 Future Work
The proposed Stencil-FSC method is a color sequence with four fields.
Optimization works have been done in the thesis to verify effective CBU suppression on the FSC-LCD. However, if the Stencil-FSC method is simplified to a three-field color sequence, it will make the Stencil-FSC method perform much better or easier to be installed on the real panel. As mentioned in section 2.2, increasing the field rate and reducing the frame duty can narrow CBU causing viewers to be less sensitive to CBU, which is helpful for CBU suppression. For example, the field rate of the Stencil-FSC four-field method is 240Hz. If the field rate is applied on the Stencil-FSC three-field method, the frame rate will be 80Hz, thus can suppress CBU more effectively. On the other hand, if the frame rate is maintain at the typical frequency, 60Hz, the field rate of the Stencil-FSC three-field method will be 180Hz, and the field duty will be longer compared to it with four fields. Therefore, it will take more time to achieve LC response and data addressing, so the panel structure can be simplified.
Consequently, the Stencil-FSC three-field method is more attractive for commercial applications, and its concept is introduced as following:
The three-field color sequence is based on the proposed Stencil-FSC method, and its first field also uses the first multi-color field of the Stencil-FSC method. Because the multi-color field is composed by the minimum value of compensated LC signal and colorful locally controlled backlight as mentioned in 3.1.3, it will display the base color image, and at least one color of red, green, and blue will be correct as shown in Fig. 6-1(b). Therefore, at least one of the three primary colors in the remnant image gotten from the subtraction between the target image and multi-color field equals zero, as in Fig. 6-1(c), so two multi-color fields will be utilized to display the remnant image of the two primary colors as shown in Fig. 6-1(d). Finally, a full-color image
can be displayed by the Stencil-FSC three-field method, as in Fig. 6-2.
However, the algorithm has two issues which need to be overcome in the future.
First, the algorithm is strongly dependent on the number of backlight divisions, and a larger number of backlight divisions is needed to achieve acceptable image performance, as in Fig. 6-3. However, large number of backlight sub-regions will cause complicated hardware and decrease the production feasibility. Therefore, an optimized algorithm is needed to be presented to overcome this issue. The second issue is that there are three different locally controlled color backlight distribution in the method, so the process of backlight distribution generation is three times complex compared it to the Stencil-FSC four-field method. Thus, simplifying the processes of three different backlights distribution is the other work needed to be done in the future.
Finally, by utilizing the Stencil-FSC three-field method and overcoming the mentioned issues in the future, the Stencil-FSC method can suppress CBU more effectively and can be much more applicable for display technology.
(a) (b)
(c) (d)
Fig. 6-1 The concept of the Stencil-FSC three-field method. (a) Target image, (b) first multi-color field of the Stencil-FSC method, (c) the remnant image, and (d) two multi-color-fields to display the remnant image.
Fig. 6-2 Stencil-FSC three-field method
(a)
(b)
(c)
Fig. 6-3 (a) Target image, (b) the Stencil-FSC three-field image and the number of backlight sub-regions equal 32*32, and (c) the Stencil-FSC three-field image with three fields and the number of backlight sub-regions equal 64*64
Reference
[1] Peter Carl Goldmark, “My Turbulent Years at CBS”
[2] T. Miyashita, P. Vetter, M. Suzuki, Y. Yamaguchi and T. Uchida, “Wide Viewing Angle Display Mode for Active Matrix LCD Using Bend Alignment Liquid Crystal Cell”, Eurodisplay 93 Digest, pp. 149-152 (1993)
[3] A. Takimoto, K. Nakao and H. Wakemoto: “Recent Progress of LCD-TVs Using OCB Mode”, IDW 04 Digest, pp. 299-302 (2004)
[4] Shuji Nakamura, Takashi Mukai, and Masayuki Senoh, “Candela-class
high-brightness InGaN/AlGaN double-heterostructure blue-light-emitting diodes”, Appl. Phys. Lett. 64, 1687 (1994);
[5] Nishida T, Ban T, Kobayashi N. “High-color-rending light sources consisting of a 350-nm ultraviolet light-emitting diode and three-basal-color phosphors ”[J]. Appl. Phy.
Lett., 2003, 82(22).
[6] Toshio Nishida, Tomoyuki Ban, and Naoki Kobayashi, “High-color-rendering light sources consisting of a 350-nm ultraviolet light-emitting diode and three-basal-color phosphors”, Appl. Phys. Lett. 82, 3817 (2003)
[7] N. Koma, T. Miyashita, T. Uchida, and N. Mitani, “Color Field Sequential LCD Using an OCB-TFT-LCD,” SID’00, pp. 632-635.
[8] F. Yamada, H. Nakamura, Y. Sakaguchi, and Y. Taira, “Color Sequential LCD Based on OCB with an LED Backlight ,” SID’00, pp. 1180-1183.
[9] Jang Jin Yoo, Jong Hoon Woo, Hyun Ho Shin, and Chang Ryong Seo, “Side Light Type Field Sequential Color LCD Using Divided Light Guide Plates,” IDRC’03, pp.
180-183.
[10] K. Sekiya, K. Wako, S. Nakano,T. Ishinabe, T. Miyashita, and T. Uchida,
“Optimized Voltage Range Selection for OCB-Mode LCD in Field Sequential Color Application,” IDW’04, pp. 97-98.
[11] Tetsuo Fukami, Seiji Kawaguchi, Shigesumi Araki, Masahiko Takeoka, and Akio Takimoto, “New Driving Method for Field Sequential Colour LCDs Using OCB Mode,” IDW’06, pp. 1617-1620.
[12] M. Mori, “Mechanism of Color Breakup on Field-Sequential Color Projectors”, SID’99, pp. 350-353.
[13] M. Ogata, K. Ukai, and T. Kawai, “Visual fatigue in congenital nystagmus caused by viewing images of color sequential projectors”, IEEE’05, pp. 314-320.
[14] J. B. Eichenlaub, “Develop and preliminary evaluation of field-sequential color LCD free of color breakup”, SID’94, pp. 293-296.
Filed-Se1uential Color Projection System for Large Area Display”, IDW’99, pp.
993-996.
[16] J. Lee, T. Jun, J. Lee, J. Han, and J. H. Souk, “Noble measurement method for color breakup artifact in FPDs”, IMID/IDMC’06, pp. 92-97.
[17] M. D. Fairchild, Color Appearance Models, 2nd Ed., Wiley-IS&T, Chichester, UK,p.1-34 (2005).
[18] R. W. Baloh, A. W. Sills, W. E. Kumely, and V. Honrubia, “Quantitative measurement of saccade amplitude, duration, and velocity”, NEUROLOGY, pp.
1065-1070 (1975).
[19] T. Jarvenpaa, “Measuring Color Breakup of Stationary Image in Field-Sequential-Color” SID ’04, pp. 82-85.
[20] T. Kurita and T. Kondo, “Evaluation and Improvement of Picture Quality for Moving Images on Field-sequential Color Displays”, IDW’00, pp. 69-72.
[21] K. Sekiya, T. Miyashita and T. Uchida, “A Simple and Practical Way to Cope With Color Breakup on Field Sequential Color LCDs ”,SID’06, pp. 1661-1664.
[22] D. Eliav, E. H. A. Langendijk, S. Swinkels, I. Baruchi, “Suppression of Color Breakup in Color-Sequential Multi-Primary Projection Displays”, SID’05, pp.
1510-1513.
[23] E.H.A. Langendijk, “A comparison of three different field sequential color displays ”, IDW’05, pp. 1809-1812.
[24] N. Koma, T. Uchida, “A new field-sequential-color LCD without moving-object color break-up”, SID’03, pp. 413-417.
[25] Roy S. Berns, Principle of Color technology, 3rd ed. , chapter 2 [26] Mark D. Fairchild, Color Appearance Models, 2nd ed. , chapter 3
[27] Louis Kerofsky, Scott Daly, Distinguished Paper: Brightness Preservation for LCD Backlight Reduction, SID 06,26.2
[28] J.H. Stessen, J.G.R. van Mourik, Algorithm for Contrast Reserve, Backlight Dimming, and Backlight Boosting on LCD, SID 06, 26.4
[29] Cheng-Yu Liao, Fang-Cheng Lin, Lin-Yao Liao, Yi-Pai Huang, and Han-Ping D.
Shieh, Inverse of Mapping Function Method for Image Quality Enhancement of Dual- Panel Displays, IDMC’06
[30] Gonzalez Woods, Digital Image Process, 2nd ed., section 8.3.2
[31] Lin, F.-C. Huang, Y.-P. Liao, L.-Y. Liao, C.-Y. Shieh, H.-P. D. Wang,
T.-M. Yeh, S.-C., “Dynamic Backlight Gamma on High Dynamic Range LCD TVs , Journal of Display Technology, 2008,Volume: 4, Issue: 2,p 139-p146”