Digital Pixel Array Adaptive Exposure Control
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Solution Overview
Problem
Image sensors face challenges in capturing images in environments with high intensity light due to saturation and blooming, which limits their dynamic range and degrades image quality, especially in wearable VR/AR/MR systems that require wide dynamic range and high-speed image generation.
Innovation Solution
An image sensor array with a controller that dynamically adjusts the exposure period for each pixel cell based on accumulated charge thresholds, preventing saturation and blooming by stopping charge accumulation when a predetermined threshold is reached, and using ADCs to generate digital pixel values from the accumulated charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the exposure period is extended to capture more light, then the image sensor can detect lower light intensities, but the pixel cells saturate in high intensity light causing blooming and degraded image quality
Solution Approach 1:
The patent implements dynamic exposure control where the exposure period is adjusted in real-time based on detected light intensity levels. The controller monitors the accumulated charges and adapts the exposure duration accordingly, extending it for low-light conditions and shortening it for high-light conditions, thereby maintaining optimal image quality across varying illumination conditions without saturation or blooming
Solution Approach 2:
The system changes the exposure time parameter dynamically based on the detected light intensity. By adjusting this critical parameter according to environmental conditions, the image sensor achieves wide dynamic range capability, capturing accurate images from very low to very high light intensities without the trade-off between extended exposure benefits and saturation risks
2Reliability
If the exposure period is shortened to prevent saturation, then image quality is maintained in high light, but the sensor cannot capture sufficient light in low intensity environments
Solution Approach 1:
The system dynamically adapts the exposure period based on real-time light intensity detection. In low-light environments, the controller extends the exposure duration to accumulate sufficient photons for accurate detection, while in high-light conditions it shortens the exposure to prevent saturation, thereby maintaining both wide dynamic range and consistent image quality across all lighting conditions
3Ease of operation
If a fixed exposure period is used, then the system operation is simple, but the sensor cannot adapt to varying light intensities causing saturation or insufficient light capture
Solution Approach 1:
The patent implements a feedback control mechanism where the controller continuously monitors the light intensity detected by the pixel cells and adjusts the exposure period accordingly. This closed-loop system automatically adapts to varying illumination conditions without requiring manual intervention, maintaining optimal performance across different lighting environments while preserving ease of operation through automated control
Solution Approach 2:
The image sensor system performs self-adjustment of the exposure period based on its own detected light intensity levels. The controller autonomously determines the appropriate exposure duration by monitoring the accumulated charges in the pixel cells, enabling the system to adapt to varying conditions without external control, thereby maintaining both simplicity and adaptability
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 extends the dynamic range of the image sensor, reducing the likelihood of saturation and blooming, enabling accurate image sensing across a wider range of light intensities and improving user experience in VR/AR/MR systems by maintaining image quality and tracking capabilities.
Implementation Method 1
A typical image sensor includes a photodiode to sense incident light by converting photons into charges (e.g., electrons or holes)
Data Source
AI summary
Methods and systems for light sensing are provided. In one example, an apparatus comprises and an array of pixel cells and a controller. Each pixel cell of the array of pixel cells includes a photodiode configured to generate charges upon receiving incident light and a capacitor configured to accumulate the charges generated by the photodiode. The controller is configured to: start an exposure period to accumulate the charges at the pixel cells; and based on a determination that the quantity of charges accumulated by the at least one pixel cell exceeds a pre-determined threshold: end the exposure period to cause the capacitors of the array of pixel cells to stop accumulating the charges, generate an output pixel value for each pixel cell based on the charges accumulated at the capacitor of the each pixel cell within the exposure period; and provide the output pixel values to generate an image frame.