Split Pixel Sensor LED Flicker Reduction via Dual Exposure
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Solution Overview
Problem
LED flicker caused by asynchronous pulse width modulation with image sensors leads to distracting and potentially dangerous displays in camera views of cars and traffic lights, necessitating effective flicker reduction techniques for high dynamic range (HDR) imaging.
Innovation Solution
The implementation of a camera system with split pixels, including large photo-diodes (LPDs) and small photo-diodes (SPDs) with varying exposure times, combined through high dynamic range imaging techniques to create a non-flickering LED image by calculating and combining images from different exposure times, ensuring consistent LED brightness perception.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If pulse width modulation is used to control LED brightness, then LED brightness control is achieved, but LED flicker occurs in captured images
Solution Approach 1:
The image sensor is divided into two distinct pixel types: first pixels with a first exposure time and second pixels with a second exposure time. This segmentation allows each pixel type to capture LED light under different exposure conditions, enabling the system to reconstruct a stable LED image by combining data from both pixel types, thereby eliminating flicker while maintaining brightness control.
Solution Approach 2:
The patent employs periodic exposure actions with different durations for first and second pixels. By alternating between short exposure (first pixels) and long exposure (second pixels) in a periodic manner synchronized with the LED pulse frequency, the system captures periodic samples of the LED signal that can be combined to eliminate flicker artifacts.
2Adaptability or versatility
If pulse frequency is lower than frame frequency, then LED control flexibility is improved, but LED pulses are missed by image sensor
Solution Approach 1:
The patent implements dynamic exposure time adjustment where first pixels use a first exposure time and second pixels use a second exposure time, with at least one being variable. This dynamic adaptation allows the system to adjust exposure durations in real-time to match varying LED pulse frequencies, ensuring accurate capture regardless of the pulse frequency being lower than frame frequency.
Solution Approach 2:
The system performs preliminary sampling with both short and long exposure times before final image reconstruction. By pre-capturing data from both pixel types with different exposure durations, the system ensures that LED pulses are captured even when pulse frequency is lower than frame frequency, maintaining measurement precision while preserving control flexibility.
3Reliability
If different exposure times are used for first and second pixels, then LED flicker is reduced, but device complexity increases
Solution Approach 1:
The patent makes the image sensor universal by implementing both first pixels and second pixels within the same sensor array, where each pixel type serves multiple functions. The first pixels capture short-duration LED pulses while second pixels capture long-duration pulses, and both contribute to the final reconstructed image. This multi-functionality reduces flicker without requiring separate imaging systems.
Solution Approach 2:
The patent merges the functionality of multiple imaging approaches into a single sensor by combining first pixels and second pixels in one image sensor device. The data from both pixel types are merged during image reconstruction to produce a final image with reduced flicker, achieving flicker reduction while minimizing the increase in device complexity through integration rather than separate systems.
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 eliminates LED flicker in captured images, enhancing safety by providing a stable and consistent visual experience, reducing the risk of misinterpreting LED flicker as emergency vehicle signals.
Implementation Method 1
an image sensor, comprising a plurality of split pixels, including pixels having a first exposure time and pixels having a second exposure time
Data Source
AI summary
A system for capturing a high dynamic range (HDR) image comprises an image sensor comprising a split pixel including a first pixel having higher effective gain and a second pixel having lower effective gain. The second pixels exposed with a capture window capture at least a pulse emitted by a light emitting diode (LED) controlled by a pulse width modulation. A first HDR image is produced by a combination including an image produced by the second pixels, and images produced by multiple exposures of the first pixels. A weight map of LED flicker correction is generated from the difference of the image produced by second pixels and the images produced by the first pixels, and the flicker areas in the first HDR image are corrected with the weight map and the image from the second pixels.