Adaptive Exposure Control for Image Sensor Dynamic Range
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Solution Overview
Problem
Current digital image sensors face challenges in achieving high dynamic range, particularly in automotive and machine vision applications, due to saturation issues and motion artifacts, and existing methods for enhancing dynamic range are memory-intensive and inefficient.
Innovation Solution
A method involving a digital image sensor with a pixel array that performs a reset operation, integrates pixels for a calibration time, reads pixel values, compares them with thresholds, and sets exposure levels based on these values, allowing for adaptive exposure control through vertical and horizontal addressing, reducing the need for multiple exposure times and memory storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If multiple exposure times are used to enhance dynamic range, then the dynamic range is improved, but memory requirements and processing complexity increase significantly
Solution Approach 1:
The patent performs a preliminary calibration exposure to determine scene brightness levels before the actual imaging exposure. This preliminary action allows the system to adaptively set the exposure time based on actual scene conditions, avoiding the need to store multiple full-resolution images for different exposure times. The calibration data is used to optimize the main exposure, thereby improving dynamic range handling while reducing memory requirements.
Solution Approach 2:
The patent extracts only the necessary exposure time information from a calibration exposure and uses it to optimize the main imaging exposure. Instead of storing and processing multiple complete images at different exposures, the system extracts the critical exposure parameter from a preliminary calibration shot and applies it to the main exposure, significantly reducing memory usage while maintaining dynamic range performance.
2Illumination intensity
If multiple exposure times are used to enhance dynamic range, then the dynamic range is improved, but processing complexity and time consumption increase
Solution Approach 1:
The system performs a quick calibration exposure to determine scene brightness levels before the main imaging exposure. This preliminary action provides the necessary information to optimally set the exposure time, avoiding the need for complex post-processing of multiple exposure images. The calibration step is computationally lightweight compared to full image processing, thereby reducing overall processing time while maintaining dynamic range performance.
Solution Approach 2:
The imaging process is segmented into a calibration phase and a main imaging phase. The calibration phase quickly determines scene characteristics, and the main phase captures the optimized image. This segmentation allows the system to perform adaptive exposure control based on preliminary data without requiring complex real-time processing of multiple full-resolution images, thereby reducing processing time and complexity.
3Illumination intensity
If adaptive exposure control is implemented per pixel, then dynamic range and image quality are improved, but device complexity increases
Solution Approach 1:
The patent implements adaptive exposure control where each pixel's exposure time is adjusted based on its local scene brightness characteristics determined during calibration. This local quality approach allows different regions of the image sensor to use different exposure times optimized for their specific lighting conditions, improving overall image quality and dynamic range while avoiding the need for complex per-pixel control circuitry through software-based adaptation.
Solution Approach 2:
The system changes the exposure time parameter adaptively based on calibration data from each pixel region. By adjusting this critical parameter based on measured scene characteristics rather than using fixed complex control circuitry, the system achieves per-pixel adaptive exposure control with minimal hardware complexity. The parameter change is driven by software algorithms that process calibration data to determine optimal exposure settings.
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 enhances the dynamic range of digital image sensors by optimizing exposure settings, reducing memory requirements, and improving signal-to-noise ratio, while maintaining efficient operation across varying light conditions.
Implementation Method 1
an image sensor may comprise a photodetector that generates a charge when radiation is incident thereupon
Data Source
AI summary
An image sensor having improved dynamic range includes a signal that is read out for a selection of pixels which act as a calibration to govern the choice of exposure levels to be applied to the rest of the array. In this way, the sensor is operable to adapt to variations in scene intensity. The pixels in the array are vertically and horizontally addressed so as to enable accounted for small areas of intensity variation across an imaged scene.