PWM Control Synchronization for Camera-LED Video Displays
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Solution Overview
Problem
LED video screens using Pulse Width Modulation (PWM) to control brightness can exhibit visible artifacts when viewed by cameras due to mismatched PWM refresh cycles and camera shutter timings, leading to issues like black bars, dark lines, and brightness variations.
Innovation Solution
A PWM control system that adjusts PWM timing and cycle duration based on camera characteristics, such as shutter open periods, to synchronize the PWM refresh cycle with the camera's exposure time, minimizing artifacts and ensuring consistent brightness perception by both cameras and human observers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If PWM refresh cycle is used to control LED brightness, then energy efficiency and brightness control are improved, but visible artifacts appear in camera-captured images
Solution Approach 1:
The system dynamically adjusts PWM timing and cycle duration based on real-time camera detection. When a camera is detected, the PWM refresh cycle is synchronized with the camera shutter speed, changing from a fixed pattern to an adaptive one that eliminates visible artifacts while maintaining energy efficiency.
Solution Approach 2:
The system changes PWM parameters (timing, cycle duration, frequency) based on detected camera characteristics. By modifying these parameters to match camera shutter speeds, the system eliminates banding and flickering artifacts in captured images while preserving the energy-efficient PWM dimming operation.
2Manufacturing precision
If PWM cycle duration is shortened to reduce artifacts, then camera capture quality improves, but human eye perception of constant brightness deteriorates
Solution Approach 1:
The system performs preliminary detection of camera presence and characteristics before adjusting PWM parameters. This allows the system to pre-synchronize PWM timing with camera shutter speeds, ensuring optimal capture quality without affecting human perception, as the adjustment is made in advance based on detected conditions.
Solution Approach 2:
The system dynamically adapts PWM parameters based on whether a camera is detected. When no camera is present, standard PWM parameters maintain constant brightness for human viewers. When a camera is detected, parameters are adjusted to synchronize with shutter speed, improving capture quality without permanently compromising either objective.
3Object-affected harmful factors
If PWM timing is synchronized with camera shutter speed, then artifact reduction is achieved, but system complexity increases
Solution Approach 1:
The system uses feedback from camera detection (via analysis of captured images or dedicated sensors) to automatically adjust PWM timing. This closed-loop approach simplifies the overall system by using intelligent detection and automatic adaptation rather than requiring complex manual configuration or multiple separate control systems.
Solution Approach 2:
The PWM control system performs self-adjustment based on detected camera characteristics. The system automatically detects camera presence, determines optimal timing parameters, and synchronizes PWM cycles without external intervention, reducing the need for additional control hardware or complex manual configuration.
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 system effectively reduces or eliminates visible artifacts in camera-captured images and maintains consistent brightness, ensuring that both cameras and human viewers do not perceive flickering or irregularities in LED video screens.
Implementation Method 1
an LED is switched between fully on (where a current is driven through the LED, emitting light at a full brightness) and fully off
Data Source
AI summary
A PWM control system includes a memory and a processor. The processor obtains characteristics of a camera capturing an image of a video display. The characteristics include a duration of a camera shutter open period. The processor calculates a PWM timing control for the display, specifying a PWM cycle duration based on the period. The processor sends a signal to the video display including the timing control and configured to control video display brightness when the camera shutter is open. The characteristics may further indicate that the camera has a global shutter. The signal may cause a plurality of PWM cycles to be output while the camera shutter is open. The signal may cause initiation of the PWM cycle based on a camera shutter synchronization signal received by the processor.