LED Sub-Period Sequencing to Reduce Rolling Shutter Dark Lines
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Solution Overview
Problem
Conventional light emission control methods using scrambled pulse width modulation (SPWM) algorithms in LEDs result in large-area scanning dark lines when captured with a rolling shutter image capturing device, leading to poor user experience due to visual artifacts.
Innovation Solution
A light emission control method that utilizes a driving circuit to manage a display with multiple sub-period sequences, determining display time units based on image grayscale values and sub-period sequences to stagger the activation of LEDs, reducing visual artifacts by averaging brightness differences through persistence of vision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If scrambled pulse width modulation (SPWM) algorithm is used to increase refresh rate and enhance grayscale contrast, then display effect is improved, but large-area scanning dark lines appear when captured with rolling shutter image capturing device
Solution Approach 1:
The frame period is divided into multiple sub-periods with different time durations, and different sub-period sequences are applied to different regions or time slots within the frame. This segmentation allows the display to distribute the activation timing of light emitting elements across multiple staggered sequences, preventing the formation of consistent scanning dark lines in captured images while maintaining grayscale contrast through controlled pulse width modulation within each sub-period.
Solution Approach 2:
The patent implements periodic switching between different sub-period sequences across consecutive display periods. By cyclically varying the sub-period sequences according to a predetermined pattern, the system creates time-varying activation patterns that average out the scanning dark line artifacts over multiple frames, while maintaining the benefits of SPWM-based grayscale control within each periodic cycle.
2Productivity
If sub-periods have different time durations for LED activation, then refresh rate and grayscale contrast are enhanced, but visual artifacts appear in captured images
Solution Approach 1:
The patent employs asymmetric sub-period sequences where different sub-periods within a frame have different time durations and activation patterns. This asymmetry is deliberately designed to distribute the scanning dark line artifacts across different spatial locations in consecutive frames, preventing the formation of large-area consistent artifacts while maintaining high refresh rates through the varied timing structure.
Solution Approach 2:
The system dynamically switches between multiple predetermined sub-period sequences across different display periods rather than using a fixed sequence. This dynamic variation in sub-period assignment creates time-varying activation patterns that cause scanning dark lines to appear at different positions in consecutive captured frames, and the human visual system averages these variations to perceive uniform brightness without noticeable artifacts.
3Object-generated harmful factors
If multiple sub-period sequences are used to stagger LED activation, then scanning dark lines are reduced, but control complexity increases
Solution Approach 1:
The patent pre-calculates and stores multiple sub-period sequences in advance before actual display operation. These predetermined sequences are prepared offline with optimized timing parameters, so that during runtime, the driving circuit only needs to select and apply the appropriate pre-defined sequence for the current display period, significantly reducing real-time computational complexity while maintaining the artifact-reduction benefits.
Solution Approach 2:
The system manages complexity by parameterizing the sub-period sequences with a small set of control variables (such as sequence index, frame counter, and region identifiers) rather than independently controlling each parameter. This parameterized approach allows the driving circuit to generate complex staggered activation patterns using simple parameter adjustments and look-up table operations, reducing the overall control complexity while achieving effective scanning dark line reduction.
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 effectively reduces visual artifacts by staggering the positions of scanning dark lines in captured frames, improving the display quality by averaging brightness differences over consecutive frames.
Implementation Method 1
a plurality of light emitting elements; determining display time unit numbers of each of the light emitting elements respectively in the sub-periods based on an image grayscale value
Implementation Method 2
reducing visual artifacts by averaging brightness differences through persistence of vision
Data Source
AI summary
A light emission control method includes steps of: A) obtaining a number (N); B) obtaining M number of sub-period sequences; C) for a current display period, selecting a first one of the M number of sub-period sequences as a current sub-period sequence, and determining display time unit numbers based on an image grayscale value contained in a to-be-displayed image, the number (N) and the current sub-period sequence; D) for a next display period, selecting a next one of the M number of sub-period sequences as a next sub-period sequence, and determining the display time unit numbers based on an image grayscale value contained in another to-be-displayed image, the number (N) and the next sub-period sequence; and E) in response to the next sub-period sequence not being an Mth one of the sub-period sequences, repeating step D).