||Both of Multi-Primary Color Pixel Arrangements and Conversion Algorithms Used to Improve Imaging Performance on LCDs
||Department of Photonics
liquid crystal displays
color conversion algorithm
human vision model
With the development in science and technology, the optimal performance for a display is essential. The image quality is one of the significant parameters to evaluate the performance of displays. Various methods are proposed to improve rendering image qualities such as multi-primary color mixing, and pixel pattern designed. The multi-primary can show more rich colors in rendering images due to four or more primary colors are employed to extend the color gamut. Various pixel patterns have different qualitative influences on the rendering images because of their different intensity distributions in the spatial frequency space. In this thesis, first of all, we focus on the arrangements of traditional RGB sub-pixel which have influence on image quality. Including analysis for modulation transfer function (MTF), pseudo colors and the performance for rendering images in high frequency condition. From the results, we can find the Green sub-pixel at the center in a pixel shows better performance than others. Second, we study the problem which promotes the luminance for displays. Adding the white sub-pixel to a pixel is one of the effective methods to enhance the luminance. In this part, we focus on the conversion algorithm from three primary colors to four primary colors. Compare with other algorithms, we can find the proposed conversion algorithm can enhance luminance without significant color shift by means of simulation and instrumental measurement on rendering images. The pseudo color phenomenon is also analyzed and discussed on the basic of human vision model. The study indicated that image performance is better when using quad RGBW with W and G sub-pixels in diagonal positions rather than them in non-diagonal positions. Except for the luminance, how to extend wide color gamut is important. In this part, we proposed a method of color mapping conversion between RGB and RGBCW to improve image luminance and maintain minimal color shift. We measured and simulated the rendered images to prove the capabilities of our proposed method. In study, the RGB-to-RGBCW mapping algorithm is designed so that the hue and saturation remains unchanged from the original color and images with higher luminance than RGB system. We also comparatively evaluate the image performance for two potential types of multi-primary color LCDs with stripe RGBCW and RGBCY pixel units, respectively. According to our simulation study and experimental results, we proved that the colors in RGBCW are similar to the original colors in RGB pixel unit including hue and saturation, which also show higher luminance than those in the RGBCY unit.
Abstract (Chinese) ........I
Abstract (English) .........II
Figure List ........X
Chapter 1 Color Science for Displays.....1
1.2 Tristimulus Values........1
1.3 CIE 1931 Chromaticity Coordinate Diagram....5
1.4 Principle of Rendering Images on LCDs....6
1.5 Human Vision Model........8
1.6 Motivation for Study.......10
Chapter 2 Study of Image Performance Rendered with Various RGB Sub.pixel Arrangements on the LCDs....11
2.1 Introduction .........11
2.2 MTF of Luminance of RGB Pixel Arrangement....12
2.3 Analysis of Color Shift of Rendering the Images of a Black Bar with a White Background Arrangement......14
2.4 Comparison of Color Uniformity of Various RGB Sub.pixel Arrangements.........16
2.5 Performance of Rendering Images with High Spatial Frequencies ...........18
2.6 Summary .........25
Chapter 3 Study of the Performance of an Image Rendered with Various RGBW Sub.pixel Arrangements and Color Conversion Algorithms on the LCDs....27
3.1 Introduction .........27
3.2 Proposed Algorithm of Color Conversion Used in RGBW LCDs with High Luminance and Small Color Shift....29
3.2.1 Simulated Pixel Units for Rendering Image....29
3.2.2 Curve Fitting of Electro.Optical Transfer Functions via Measurement ...........30
3.2.3 Illustration of the Proposed Color Conversion Algorithm...32
3.2.4 Accuracy of Our Proposed Color Mapping Conversion...35
3.2.5 Evaluation of Rendering Images with Respect to Simulated RGB and RGBW Pixel Units via Visual Perception and Color Measurements ..........37
3.2.6 RGB to RGBW Color Conversion of Other Groups....40
3.2.7 Decreased Luminance in an RGBW System....42
3.2.8 Threshold Value Selection for Our Proposed Color Conversion Algorithm.........43
3.2.9 Comparison of Imaging Performance Rendered with Other Algorithms..........45
3.3 Optimal RGBW Sub.pixel Arrangements on the LCDs with Quad Pixel Units ........51
3.3.1 Consideration with Human Vision Effect in Rendering Images..51
3.3.2 Analysis and Discussion of the Pseudo Color Phenomenon in Rendering Images.........53
3.4 Summary .........56
Chapter 4 Study of Color Conversion Algorithm from RGB to RGBCW and Comparison between Stripe RGBCW and RGBCY Patterns.......58
4.2 Five Primary Color RGBCW LCDs......60
4.2.1 Pixel Units for Rendering Images and Color Gamut...60
4.2.2 Illustration of the Proposed Color Conversion Algorithm..61
4.2.3 Comparison and Evaluation of the Rendered Images by the RGB and RGBCW Color System Using the Proposed Algorithm...68
4.2.4 Significant Phenomenon of Color Imaging Performance Related to Both Sub.pixel Arrangements and White Sub.pixel Signals....71
4.3 Comparative Evaluation of the Imaging Performance of Multi.Primary Color LCDs with RGBCW and RGBCY Pixel Units by Simulation........76
4.3.1 Simulation of Pixel Units and Selection of Multi.primary Colors for Image Rendering........76
4.3.2 Comparison of Image Rendering by Visual Perception and Experimental Measurements........78
4.3.3 Analysis of Pseudo Color Phenomena in Image Rendering...82
4.4 Analysis of Color shift between Original and Simulated Color Checkers .........84
4.5 Summary .........85
Chapter 5 Future Work........87
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