C ONCLUSION

Reducing power consumption while enhancing image quality was successfully demonstrated using Stencil-FSC methods based on a dual-panel structure: a low resolution controllable RGB-LED backlight and a high resolution LC panel. The dual-panel provided more flexibility to present a vivid image or video. The backlight module first displayed a colorful, high contrast image, and then a high optical throughput LC panel maintained image details. The well-combined structure invalided the argument of using two optical structures to display an image. Following, this chapter reviewed the proposed methods of backlight module

and the whole LCD system including the dynamic backlight and the color filter-less LC panel (Fig. 6-1).

Fig. 6-1 Whole schema of final dissertation results.

6.1.1 Backlight Module: IMF for Dynamic Backlight Control

Differing from prior backlight determination methods, the inverse of a mapping function (IMF) method provided “dynamic” gamma functions for each input image to produce high contrast images. The IMF method was demonstrated on a 37-inch HDR-LCD.

The experimental results achieved a high contrast ratio (~20,000:1) image, preserved clearer image details with low distortion (D=3.17%) compared to the prior backlight methods. Furthermore, IMF still maintained high brightness to present a more vivid image for human vision with an average power reduction of 30% compared to an LED full-on backlight LCD (~190W).

6.1.2 LC Panel: Color Filters Removed

For the LC panel, the optical throughput was further enhanced by a factor of 3 while getting rid of color filters in an FSC-LCD, as illustrated in Fig. 6-2. However, a lethal issue, color breakup (CBU) degraded image clarity and caused viewer discomfort. Most prior CBU suppression methods involved either inserting additional mono-color fields or

IMF CF‐less

Full‐on CCFL Dynamic RGB‐LED

Stage 1 Stage 2

Dynamic BL: IMF Pavg= 130 W  CR≈20,000:1 Stencil‐FSC

Pavg< 35 W CR>20,000:1 Color Gamut=114%

Applied

increasing the field rate. Unfortunately, LC response time prevented the implementation of these methods in large-sized FSC-LCDs.

Fig. 6-2 Comparison of optical throughputs between a conventional LCD (top) and a color filter-less LCD (FSC-LCD).

6.1.3 Whole LCD System Based on Stencil-FSC Methods

In order to efficiently suppress CBU, the Stencil-FSC method ingeniously applied local color-backlight dimming technology to an FSC-LCD. The originality of Stencil-FSC was to use a multi-color image concentrating image luminance in a single field. The intensities of the residual primary-color sub-images were therefore greatly reduced. Using this concept, two field rates, 240Hz (4-field) and 180Hz (3-field), Stencil-FSC methods were demonstrated. Through simulations, CBU was suppressed by 50% for eighty test images when compared to conventional RGB-driving and made CBU almost imperceptible in experimental photos.

240Hz Stencil-FSC was realized on a 32-inch OCB-mode FSC-LCD which demonstrated in 35 Watts average power consumption, and a wide color gamut of 114%

NTSC. Using the test image, Lily, 240Hz Stencil-FSC yielded a high static contrast of 26,000:1, power consumption of less than 28 Watts.

100%

Furthermore, the field rate was reduced to 180Hz to make Stencil-FSC more feasible. A green-based multi-color image replaced the multi-color image of 240Hz Stencil-FSC.

Therefore, the luminance of residual red and blue color images was also greatly reduced.

The average power consumption was further reduced to less than 35 Watts because only three fields were required. The features of low field rate, simple, and direct algorithm processing made the 180Hz Stencil-FSC method more feasible in a color filter-less LCD.

In summary, Stencil-FSC successfully improved three main drawbacks of conventional LCDs: low optical throughput, imperfect dark state, and low color saturation. The experimental results verified a Stencil-FSC LCD has strong potential for future large-sized

“Eco-Display” applications.

Table 6-1 Dissertation comparisons between objectives and results on a 32-inch LCD.

6.2 Remaining Issues

Comparing the results with the objectives of this dissertation, the 180Hz Stencil-FSC method almost reached all the objectives except for a minor issue in image fidelity, as shown in Table 6-1. To reduce the field rate from 240Hz to 180Hz, the green-field content was

Objectives Stencil‐FSC

Status

240Hz 180Hz

Contrast Ratio > 20,000 : 1 26,000 : 1 26,000 : 1

(estimated) V

Color Gamut 

(% NTSC) > 110 114 114 V

Power 

Consumption (W) 55 35 < 35

(estimated) V

Color Breakup 

(Relative CBURGB) Imperceptible Imperceptible 

(52.1%)

Imperceptible 

(52.7%) V

Field Rate (Hz) 180 240 180 V

Image Fidelity Good Good Acceptable Δ

Ps: Power of conventional 32‐inch LCDs (W) : CCFL‐BL     110 LED‐BL      190

However, an issue resulted from only choosing green information as the base color for all images. The issue was especially apparent in the image which contained abundant green information, such as illustrated in the purple circle of Fig. 6-3. To quantify the color distortion, a pixel distorted ratio (PDR(ΔE00>3)) is given by Eq. 6-1 which is defined as the ratio of the number of distorted pixels divided by the number of total pixels, where a distorted pixel means that its pixel color difference is larger than the acceptable value (ΔE00>3).

pixels 100%

# of total

pixels distorted

# of color 3

ΔE

PDR( ₀₀ > )≡ × (6-1)

For the two test images, Butterfly and Lotus, their pixel distorted ratio (PDR(ΔE00>3)) were 46% and 40% respectively which was equivalent to half number of total pixels were distorted and reduced green color saturation. As mentioned in section 5.1.1, the first field LC signals were taken from green color; in this case, the red and blue color LC signals were lower than green LC signals. Therefore, even though the red and blue backlight intensities under the purple circles were low, the red and blue lights also propagated through the first field and contributed redundant luminance resulting in reduction of green color saturation.

(a) Original images (b) Simulated images (c) Error images

Fig. 6-3 Redundant red or blue light propagates through in the first green-based field-image resulting in reduction of green color saturation, especially in the purple circle. (a) Two test images of Butterfly and Lotus. (b) Simulated images after the 180Hz Stencil-FSC processing. (c) CIEDE2000 error images between test and processed images with PDRs(ΔE00>3) of 46% and 40% respectively.