Polynomial Gamma Correction Circuit for Display Devices
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Solution Overview
Problem
Conventional liquid crystal display technologies face challenges in instantly switching gamma values to adapt to changing environmental conditions, such as varying light intensities, due to the complexity and size of circuitry required for gamma correction, particularly in portable devices where quick adjustments are necessary for optimal visibility.
Innovation Solution
A display device incorporating a correction circuit that uses polynomials for gamma correction, where input gray-scale data are variables and coefficients are adjusted based on environmental sensor outputs, eliminating the need for complex operation circuits and large lookup tables, allowing for rapid switching of correction curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a look-up table (LUT) is used for gamma correction, then the correction can be realized without directly executing exponentiation, but the LUT size needs to be increased to perform gamma correction for different gamma values
Solution Approach 1:
The patent segments the gamma correction process into two parts: a small LUT that stores only correction data for specific gray-scale values (0, 128, 255), and a linear interpolation process that calculates correction data for intermediate values. This segmentation allows the LUT size to be reduced from storing all 256 gray-scale correction values to storing only 3 key correction values, while still achieving accurate gamma correction for all gray-scale levels through interpolation.
2Measurement precision
If different gamma values are used for R, G and B respectively, then the color tone of the display image is improved, but the circuit size increases
Solution Approach 1:
The patent implements a universal gamma correction approach where a single polynomial correction circuit is used for all three color channels (R, G, B). The correction polynomial coefficients are adjusted based on the input color channel to achieve channel-specific gamma correction. This allows different gamma values to be applied to each color channel while using a single shared correction circuit structure, thus maintaining color tone accuracy without increasing circuit size proportionally.
Solution Approach 2:
The patent changes the parameters (coefficients) of the correction polynomial based on the input color channel (R, G, B) and desired gamma value. By dynamically adjusting the polynomial coefficients rather than using separate fixed circuits for each color channel, the system achieves color-specific gamma correction with a unified circuit structure, reducing overall circuit complexity.
3Measurement precision
If a complex arithmetic operation circuit is used to execute exponentiation rigorously, then accurate gamma correction is achieved, but the circuit cannot be mounted to a liquid crystal driver
Solution Approach 1:
The patent replaces the complex, expensive exponentiation circuit with a simpler, more implementable polynomial calculation circuit. While polynomial approximation is not mathematically identical to exponentiation, it provides sufficient accuracy for display applications and is much more suitable for integration into liquid crystal driver circuits with limited resources and area constraints.
Solution Approach 2:
The patent substitutes the mathematical operation of exponentiation with a polynomial calculation system. Instead of implementing the complex exponential function, the system uses a polynomial approximation (Taylor series expansion) that is computationally simpler and more suitable for hardware implementation in display drivers, while maintaining adequate correction accuracy.
4Measurement precision
If the gray-scale voltage is adjusted in consideration of V-T characteristics, then precise correction is realized, but it is difficult to adjust the gray-scale voltage and not suitable for different gamma values in R, G and B
Solution Approach 1:
The patent implements a dynamic gamma correction system where the correction polynomial coefficients are not fixed but are adjusted based on the input color channel and desired gamma value. This dynamic adjustment capability allows the same correction circuit to adapt to different gamma requirements for R, G, and B channels, as well as to different overall gamma values, making the system versatile while maintaining precision through polynomial approximation.
Data Source
AI summary
A display device includes a display panel, an environmental sensor, a correction circuit and a driving circuit. The correction circuit is configured to generate a corrected gray-scale data on the basis of input gray-scale data. The driving circuit is configured to drive the display panel in response to the corrected gray-scale data. The correction circuit generates the corrected gray-scale data by executing a correction using a polynomial in which the input gray-scale data are used as variables. Coefficients of the polynomial are changed in response to an output signal of the environmental sensor.