Gamma Correction Circuit with Sub-LUT Switching for LCD Drivers
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Solution Overview
Problem
Conventional techniques fail to simultaneously achieve accurate gamma correction and instant switching of gamma values in liquid crystal displays, leading to increased circuit complexity and cost, as well as difficulties in achieving natural image rendering due to large differences in gradation data values.
Innovation Solution
A display apparatus with a correcting circuit that performs gamma correction using a correction calculation equation with coefficients determined by correction data, allowing for the selection of different calculation equations based on input gradation data and correction data, and includes a memory section for storing and transferring correction data to instantly switch gamma curves.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a look-up table (LUT) is used for gamma correction with multiple gamma values, then gamma correction accuracy is improved, but the LUT size increases significantly making it difficult to incorporate in the liquid crystal driver
Solution Approach 1:
The LUT is divided into multiple sub-LUTs, each storing correction data for a specific gamma value. Instead of using one large LUT to store all correction data for multiple gamma values, the correction data is segmented into separate sub-LUTs. The controller selects and switches between these sub-LUTs based on the required gamma value, significantly reducing the size of each individual LUT while maintaining the capability to perform accurate gamma correction for multiple gamma values.
2Measurement precision
If exact power multiplication calculation is performed for gamma correction, then correction accuracy is improved, but circuit complexity increases making it unsuitable for liquid crystal driver integration
Solution Approach 1:
Instead of performing exact power multiplication calculations which require complex circuits, the patent uses pre-calculated correction data stored in sub-LUTs. The controller copies the appropriate correction data from the selected sub-LUT corresponding to the input gradation data and applies it to achieve gamma correction. This approach replicates the effect of exact power multiplication through pre-computed values, maintaining accuracy while avoiding complex real-time calculation circuits.
3Manufacturing precision
If different gamma values are used for R, G, and B colors, then color tone quality is improved, but the number of LUTs required increases making hardware implementation difficult
Solution Approach 1:
The sub-LUTs are designed to be color-independent and can be used for correcting gradation data for all colors (R, G, and B). Instead of requiring separate LUTs for each color and each gamma value, the patent uses a set of universal sub-LUTs that can serve multiple colors. The controller selects the appropriate sub-LUT based on the gamma value required, and the same sub-LUT can be applied to correct gradation data for any color channel, significantly reducing the total number of LUTs needed while maintaining color tone quality.
Data Source
AI summary
A display apparatus includes a display panel; a correcting circuit configured to carry out gamma correction on input gradation data in response to correction data which specifies a shape of a gamma curve to generate output gradation data; and a driving circuit configured to drive the display panel in response to the output gradation data from the correcting circuit. The correcting circuit carries out approximation calculation for the gamma correction based on the input gradation data by using a correction calculation equation whose coefficients are determined based on the correction data, and the correction calculation equation is switched based on a value of the input gradation data and a value of the correction data.