LCD Backlight Control via Segmented Block Dimming
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Solution Overview
Problem
LCD TVs face poor 'black level' representation and degraded contrast ratio due to backlight leakage, which is inherent in their structure, especially when pixel grayscale values are zero, leading to inefficient backlight control.
Innovation Solution
A method for controlling backlight brightness in LCDs by determining composite grayscale values for blocks of pixels, identifying block motion, and applying specific brightness functions to adjust PWM duty ratios, thereby reducing backlight leakage while preserving original luminance levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If backlight is set to maximum brightness, then luminance is sufficient, but backlight leakage occurs and black level representation deteriorates
Solution Approach 1:
The patent divides the backlight into multiple independently controllable dimmable blocks (e.g., 5-10 blocks across the panel width) rather than a single uniform backlight. Each block can be dimmed independently based on the grayscale values of pixels within its region, allowing selective reduction of backlight in areas with dark pixels while maintaining brightness in areas with light pixels, thus reducing overall backlight leakage while preserving sufficient luminance where needed.
Solution Approach 2:
The patent applies different backlight brightness levels to different spatial regions of the display based on local image characteristics. By analyzing the composite grayscale values of pixel blocks within each dimmable block region, the system adjusts backlight intensity locally - dimming regions with predominantly dark pixels while maintaining full brightness in regions with light pixels, thereby achieving local optimization of both luminance and leakage reduction.
2Object-affected harmful factors
If backlight is dimmed to reduce leakage, then black level improves, but overall brightness and luminance are reduced
Solution Approach 1:
By segmenting the backlight into multiple dimmable blocks, the system can dim only specific regions where leakage is problematic (those with low composite grayscale values) while keeping other regions at full brightness. This selective dimming approach reduces overall leakage without sacrificing the luminance of bright areas, resolving the trade-off between leakage reduction and brightness maintenance.
Solution Approach 2:
The system applies local quality adjustment by determining different backlight brightness levels for different spatial regions based on their respective image content characteristics. Regions with dark pixels receive reduced backlight to minimize leakage, while regions with light pixels maintain full backlight intensity to preserve luminance, achieving both leakage reduction and brightness preservation simultaneously.
3Measurement precision
If LED backlight controllable units are increased to match pixel granularity, then local control precision improves, but device complexity and cost increase
Solution Approach 1:
The patent implements a middle-ground segmentation approach by dividing the backlight into a moderate number of dimmable blocks (e.g., 5-10 blocks across the panel width) rather than matching pixel-level granularity. This provides sufficient local control capability to address leakage in different regions while avoiding the excessive complexity and cost associated with per-pixel or near-per-pixel backlight control, achieving an optimal balance between control precision and system complexity.
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
This approach effectively reduces backlight leakage and maintains high contrast ratio and brightness by adaptively dimming the backlight only when necessary, ensuring accurate 'black level' representation and improved image quality.
Implementation Method 1
an LC (Liquid Crystal) cannot illuminate by itself and requires light aids illuminating behind the LC panel
Implementation Method 2
Light Emitting Diode (LED) backlights
Implementation Method 3
The level (e.g., the Pulse Width Modulation (PWM)) of duty ratio of the electrical signal on this conductor controls the viewer-perceived (i.e., time-averaged) brightness of all the LEDs in that group
Data Source
AI summary
To improve contrast ratio of the image on a backlit display plane such as a liquid crystal display (“LCD”), each area of the image that has separately controllable backlight may be given full backlight until an average or composite brightness of the image in that area is less than a threshold value at which light leakage through the image from full-strength backlight begins to be noticeable by a viewer. For image areas with composite brightness less than that threshold, backlight brightness may be reduced in proportion to how much below the threshold the area's composite image brightness is. Backlight brightness may also be adjusted for other image aspects such as (1) the presence of bright pixels in an otherwise relatively dark area, (2) whether the area is adjacent to one or more other areas in which the image information is in motion, and/or (3) time-averaging of image information over several successive frames of such information.