Color breakup phenomenon is a fatal drawback of FSC-LCDs; this phenomenon causes discomfort in human eyes and degrades image quality. Therefore, color breakup suppression has been a major research in the FSC technique. Many color breakup suppression methods were proposed in different ways which can be categorized into inserting mono-color field, motion compensation, and inserting multi-color field as shown in Fig. 2-8.
Fig. 2-8 Prior color breakup suppression methods of FSC-LCD.
In the inserting mono-color field part, the first one is to increase the field rate to 360Hz (such as RGBRGB or RGBKKK) [23] [24] or higher, the width of separated rainbow-like colors occurred at the edge of an image can be reduced on retina while eyes movement as simulated images in Fig. 2-9. This method are usually be utilized in the DLP projector with color wheel and its digital micro-mirror device (DMD). The second one is to insert complementary color field to original three primary fields (RGBCY), this can reduce the color difference between each field and prevent from appearance of the sensitive color at the edge of images as shown in Fig. 2-10. However, increasing high field rate might be not feasible in current LC response time.
(a) 180Hz RGB (b) 360Hz RGBRGB
Fig. 2-9 Simulation color breakup image of (a) 180Hz RGB, and (b) 360Hz RGBRGB.
(a) 180Hz RGB (b) 300Hz RGBCY
Fig. 2-10 Simulation color breakup image of (a) 180Hz RGB, and (b) 300Hz RGBCY.
Motion compensation method was proposed to solve the dynamic color breakup phenomenon effectively. Fig. 2-11 shows the mechanism of motion compensation [24]. The method is to display each field with a proper shift according to the moving velocity of input image, after human eye integration color breakup can be suppressed effectively. However, if some objects have a chance to cross the observer’s tracking object in an opposite direction as shown in Fig. 2-12, the perceived momentary image of the crossing object gets worse color breakup than conventional RGB-driving method.
Fig. 2-11 The mechanism of motion compensation; color breakup was suppressed effectively.
Fig. 2-12 The mechanism of motion compensation; object and observer’s eye trace movement in the opposite position.
The color breakup suppression methods as mentioned above can be effectively solved the color breakup phenomenon, but those are hard to implement on hardware due to the LC
response time is not fast enough to be implemented in current commercial display products.
In order to implement FSC method on hardware, the field rate must be further reduced to lower rate. Therefore, our team proposed Stencil-FSC methods which the field rate is lower than 240Hz and with multi-color single field to suppress color breakup effectively [25] [26]
[27]. Fig. 2-13 shows the Stencil-FSC methods with different field images proposed by our group. The concept of 240Hz Stencil-FSC method is to display majority information of input image with high luminance and rough color in the first field. The other two fields were display the detail of the remaining information with lower luminance. Therefore, the perceived luminance of the separated color at the edge of image was decreased and almost imperceptible. Comparing to the color breakup phenomenon of RGB-driving method as shown in Fig. 2-14(a), the color breakup phenomenon of 240Hz Stencil-FSC method was shown in Fig. 2-14(b).
Because of 240Hz field rate is still a little high to be hard implemented in large size FSC-LCDs. Therefore, our team proposed the 180Hz Stencil-FSC method to further improve this issue. The concept of the 180Hz Stencil-FSC method is due to human eye is most sensitive to green color, hence all green information plus some parts of red and blue information are displayed in the first field. The remaining red and blue information are displayed in the second and third field. Therefore, when color breakup phenomenon is perceived, the separated rainbow-like edge is almost without green information, color breakup phenomenon is almost imperceptible as shown in Fig. 2-14 (c). In current 180Hz Stencil-FSC can be implemented in the OCB mode of LC in large size display.
In order to implement Stencil-FSC in commercial LC mode like TN, VA, MVA, IPS ...etc., our team proposed 120Hz two-color-field method. The concept of 120Hz two-color-field method is due to human eye is less sensitive to blue color, hence red and a part
phenomenon is also suppressed with less image distortion. The comparison of color breakup phenomenon between RGB-driving method and 120Hz two-color-field method are shown in Fig. 2-15 (a) and Fig. 2-15 (b).
(a) 240Hz Stencil-FSC (b) 180Hz Stencil-FSC (c) 120Hz Two-color-field
Fig. 2-13 The concept of Stencil-FSC methods: (a) 240Hz Stencil-FSC (b) 180Hz Stencil-FSC, and (c) 120Hz Two-color –field FSC.
(a) Color breakup image of RGB-driving method with target image Girl
(b) Color breakup image of 240Hz Stencil-FSC method with target image Girl
(c) Color breakup image of the 180Hz Stencil-FSC method with target image Girl Fig. 2-14 Color breakup of image Girl by different FSC methods: (a) RGB-driving, (b) the 240Hz Stencil-FSC method, and (c) the 180Hz Stencil-FSC method.
(a) Color breakup image of two-color-field method with target image Color Ball
Fig. 2-15 Color breakup of image Color Ball by (a) RGB-driving, and (b) 120Hz two-color-field method.