RGBW LCD Luminance Adjustment Using Dual EOTF Lookup Table
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Solution Overview
Problem
RGBW liquid crystal displays (LCDs) face challenges in displaying high-quality images with high dynamic range (HDR) due to their poor dark state characteristics and higher maximum luminance values, which affect luminance recognition and grayscale image display, especially under varying ambient light conditions.
Innovation Solution
A luminance adjustment method and apparatus that utilize different electro-optical transfer functions (EOTFs) for grayscale intervals, generating a lookup table to adjust luminance based on a standard gamma curve and a custom EOTF with increased slope for higher luminance levels, improving display capability in high grayscale images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the LCD follows the traditional gamma curve with gamma value equal to 2.2, then the grayscale and luminance curves match the electro-optical characteristics of traditional CRT display, but the luminance recognition capacity for high luminance area is affected and fails to show quality HDR images
Solution Approach 1:
The patent divides the grayscale range into multiple intervals (first grayscale interval and second grayscale interval) with different gamma values. The first interval uses gamma=2.2 for compatibility with traditional displays, while the second interval uses gamma=1.8 to enhance luminance recognition in high brightness areas, thus resolving the contradiction between compatibility and luminance precision
Solution Approach 2:
Different gamma values are applied to different grayscale intervals based on local requirements. Low grayscale values use gamma=2.2 to maintain traditional display characteristics, while high grayscale values use gamma=1.8 to improve luminance recognition, achieving local optimization for both compatibility and HDR quality
2Measurement precision
If the LCD uses a new EOTF with 10 bits coding for maximum luminance of 10000 nits, then HDR image display capability is improved, but the poor dark state characteristics of LCD and non-ideal birefringence and polarization characteristics prevent optimal performance in low luminance interval
Solution Approach 1:
The patent segments the grayscale range into two intervals with different gamma characteristics. The first interval (0-128) uses gamma=2.2 to address poor dark state performance, while the second interval (128-255) uses gamma=1.8 to enable HDR display capability, thus resolving the contradiction between dark state reliability and HDR precision
Solution Approach 2:
The patent changes the gamma parameter from a fixed value to a piecewise function with different values for different grayscale intervals. This parameter change allows the system to optimize for dark state performance in low grayscale values while achieving HDR capability in high grayscale values
3Illumination intensity
If the LCD has higher maximum luminance value (700-1200 nits for RGBW), then luminance and transmittance levels are greatly increased, but the human eye can only identify larger luminance differences in high luminance interval, affecting image quality
Solution Approach 1:
The patent changes the gamma parameter for high grayscale intervals to 1.8, which creates a steeper luminance curve that better matches the human eye's luminance recognition characteristics in high brightness areas, thus improving luminance difference recognition precision while maintaining high maximum luminance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enhances the display capability of RGBW LCDs by optimizing luminance adjustment across different grayscale intervals, improving HDR display and addressing poor dark state performance, with the custom EOTF increasing luminance differences in high luminance areas for better image recognition.
Implementation Method 1
the luminance of the grayscale needs to be controlled by incorporating birefringence effect of the liquid crystal molecules
Implementation Method 2
the luminance of the grayscale needs to be controlled by incorporating birefringence effect of the liquid crystal molecules and polarization characteristics of the polarizer
Data Source
AI summary
The invention provides a luminance adjustment method and apparatus for RGBW LCD, which uses first and second EOTFs to generate a grayscale luminance lookup table for RGBW LCD, and makes the grayscale-luminance relation in lookup table corresponding to the first EOTF within the grayscale interval between 0 and grayscale threshold; the grayscale-luminance relation in lookup table corresponding to the second EOTF within the grayscale interval between grayscale threshold and 255; the curve slope of the second EOTF greater than the curve slope of the first EOTF within the interval between second luminance threshold and maximum luminance value. By adopting different EOTFs for low and high grayscale intervals, the method considers the poor dark state characteristics of LCD and characteristics of RGBW LCD having higher maximum luminance, and improves the display capability of RGBW LCD in details of high grayscale images.