LED Tile Display PWM Synchronization for Rolling Shutter Capture
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Solution Overview
Problem
Capturing moving images of LED displays using cameras with rolling shutters often results in artifacts due to misalignment between the camera's exposure cycle and the LED's pulse width modulation (PWM) control, which causes pulsing or banding artifacts.
Innovation Solution
The method involves dividing each image capture frame into time slices and controlling the video control signal to be off during partial shutter periods and on during open shutter periods, aligning the signal with the camera's shutter timing to minimize artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If LED displays use PWM control with multiplexing scan groups, then power consumption is reduced and display efficiency is improved, but rolling shutter cameras capture pulsing or banding artifacts due to misalignment between shutter timing and LED pulse timing
Solution Approach 1:
The system performs preliminary synchronization by detecting the PWM control signal timing and pre-calculating the optimal shutter timing parameters before image capture begins. This advance preparation ensures that the rolling shutter timing is pre-adjusted to align with LED pulse cycles, preventing artifacts without requiring real-time adjustments during capture
Solution Approach 2:
The system implements feedback by detecting the actual PWM control signal from the LED display and using this information to dynamically adjust shutter timing parameters. The system continuously monitors the relationship between shutter timing and LED pulse timing, making real-time corrections to eliminate pulsing or banding artifacts while maintaining power-efficient PWM operation
2Measurement precision
If the shutter speed is increased to reduce motion blur, then image clarity is improved, but the exposure time becomes too short to capture the rapid LED pulses, worsening the artifacts
Solution Approach 1:
The system changes the timing parameters of the shutter by detecting PWM signal characteristics and dynamically adjusting shutter start and end times within each frame. This parameter adjustment aligns the exposure window with LED pulse cycles, allowing the shutter to capture complete pulse periods even at high shutter speeds, thereby eliminating artifacts while maintaining image clarity
3Stability of the object's composition
If the PWM frequency is increased to improve display smoothness, then visual quality for live viewers is improved, but the LED pulses become too rapid to be fully captured by the rolling shutter, increasing artifacts
Solution Approach 1:
The system performs preliminary detection and analysis of the PWM control signal frequency and timing characteristics before capture. By pre-measuring these parameters, the system can calculate the optimal shutter timing configuration in advance, ensuring that even high-frequency PWM signals are captured complete cycles without artifacts
Solution Approach 2:
The system uses feedback from continuous detection of the PWM control signal to dynamically adapt shutter timing parameters. This feedback mechanism allows the system to respond to varying PWM frequencies and maintain proper synchronization, ensuring display smoothness for live viewers while preventing capture artifacts
Data Source
AI summary
Systems and methods for moving image capture from video displays are disclosed. In particular, systems and methods for synchronizing display and camera timing so as to reduce or eliminate artifacts appearing in the captured moving images due to unsynchronized interaction between camera shutter/exposure timing and the timing of the display control signal.