LCD Backlight Local Dimming for Halo and Clipping Control
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Solution Overview
Problem
Existing local dimming control methods for LCDs face challenges in adjusting the duty cycle of driving signals to minimize halo and clipping effects, particularly in areas with varying brightness and light diffusion, leading to suboptimal display quality.
Innovation Solution
A local dimming control method and device that calculates an initial duty cycle for light emitting diodes in a backlight module, considers light diffusion, and adjusts the duty cycle based on a cost function gradient to minimize clipping and leaking errors, using a processor to execute modules for calculating brightness, local luminance, and adjusting the duty cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the duty cycle is adjusted based on blending of max brightness and average brightness, then the brightness control is simplified, but the halo phenomenon becomes stronger and display quality deteriorates
Solution Approach 1:
The patent applies local quality by calculating local luminance for each light emitting diode based on its specific position and the light diffusion characteristics of surrounding diodes. Instead of uniform brightness control, each LED's duty cycle is individually adjusted according to its local environment, thereby reducing halo effects while maintaining manageable control complexity through systematic local optimization.
Solution Approach 2:
The patent changes the control parameter from simple average brightness blending to local luminance calculation that incorporates light diffusion parameters. By introducing the local luminance parameter that considers surrounding LED effects, the system achieves better display quality without excessive complexity increase, as the parameter change enables precise local control.
2Illumination intensity
If the duty cycle is set to maximum (100%) in bright areas to represent white, then the brightness representation is improved, but clipping increases and peak intensity cannot be reached
Solution Approach 1:
The patent implements feedback by calculating the cost function gradient based on the difference between local luminance and ideal brightness. This gradient information provides feedback for adjusting the duty cycle, allowing the system to iteratively optimize brightness representation while avoiding excessive clipping. The feedback mechanism enables precise control that maintains peak intensity accuracy while achieving good brightness representation.
Solution Approach 2:
The patent applies partial action by adjusting duty cycles based on local luminance requirements rather than uniformly setting all bright areas to maximum. By calculating individual duty cycles for each LED based on its specific local luminance and the cost function gradient, the system achieves adequate brightness representation without the excessive action of setting everything to 100%, thereby maintaining peak intensity accuracy.
3Measurement precision
If iterative calculations are used to adjust duty cycle, then the optimization precision is improved, but the calculation time and complexity increase
Solution Approach 1:
The patent applies preliminary action by pre-calculating the light diffusion characteristics of surrounding light emitting diodes and incorporating them into the local luminance calculation. This preliminary preparation of diffusion parameters allows the system to achieve high optimization precision without requiring extensive iterative calculations during operation, as the diffusion effects are already accounted for in the initial local luminance computation.
Solution Approach 2:
The patent substitutes iterative mechanical calculation processes with a direct mathematical solution approach. By formulating the duty cycle adjustment as a gradient-based optimization problem that incorporates pre-calculated light diffusion parameters, the system replaces time-consuming iterative calculations with a more efficient direct computation method that achieves comparable precision with reduced calculation time.
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
The method allows for quick and proper adjustment of the duty cycle, reducing clipping and leaking errors, thereby enhancing display quality by considering light diffusion and image characteristics, without the need for iterative calculations.
Implementation Method 1
a backlight module having a plurality of light emitting diodes, each light emitting diode is configured to provide light to one pixel in a display panel
Implementation Method 2
calculating a local luminance of each light emitting diode based on combination of brightness of that light emitting diode and light diffusion of surrounding light emitting diodes
Data Source
AI summary
A local dimming control method for a backlight module having a plurality of light emitting diodes is provided. The local dimming control method includes the steps of determining an initial duty cycle of a driving signal, calculating brightness of each light emitting diode according to the initial duty cycle, calculating a local luminance of each light emitting diode based on combination of brightness of that light emitting diode and light diffusion of surrounding light emitting diodes, calculating a cost function of clipping error and leaking error according to the local luminance of each light emitting diode and an ideal brightness of the corresponding pixel, calculating a gradient of the cost function of clipping error and leaking error, and adjusting the initial duty cycle according to the gradient, and image characteristics of the pixel and the surrounding pixels to provide an adjusted duty cycle of the driving signal.