Rolling Shutter Image Sensor ROI Mode for Motion Blur
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Solution Overview
Problem
Rolling shutter image sensors are prone to distortion and motion blur in vehicle occupant monitoring systems due to staggered exposure times, making them unsuitable for applications requiring accurate subject movement detection and classification, especially when using pulsed IR illumination to avoid heat buildup.
Innovation Solution
Implementing a rolling shutter image sensor that operates in Region of Interest (ROI) mode with controlled exposure parameters, allowing for short exposure times to prevent motion blur and swapping between color and monochrome modes based on ambient light levels, while using pulsed IR illumination to improve image quality and reduce noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a rolling shutter image sensor is used with pulsed IR illumination to avoid heat buildup, then energy efficiency is improved, but image quality deteriorates due to motion blur from staggered exposure times
Solution Approach 1:
The image sensor is divided into multiple row groups that are exposed and read out in sequential segments. By controlling the exposure timing and synchronization with pulsed IR illumination, each row group captures light during the brief illumination window, enabling energy-efficient operation while maintaining image quality through coordinated segment exposure.
Solution Approach 2:
The system employs periodic pulsed IR illumination synchronized with the rolling shutter exposure cycles. The illumination pulses are timed to coincide with the exposure windows of different row groups, ensuring that all segments receive adequate light during brief, periodic intervals rather than requiring continuous illumination.
2Stability of the object's composition
If exposure time is extended to allow pulsed IR illumination of all rows, then illumination uniformity is improved, but motion blur increases
Solution Approach 1:
The exposure timing for each row group is predetermined and pre-synchronized with the pulsed IR illumination schedule. The system plans the exposure sequence in advance, assigning specific time windows to specific row groups, ensuring that illumination uniformity is achieved through coordinated timing rather than extended exposure durations.
3Manufacturing precision
If all rows are exposed simultaneously as in global shutter, then image sharpness is improved, but heat management deteriorates due to continuous illumination requirements
Solution Approach 1:
Instead of exposing all rows simultaneously which would require continuous illumination and generate heat, the sensor divides rows into segments that are exposed sequentially. This segmentation allows the use of brief pulsed illumination, reducing overall heat generation while still capturing sharp images of moving subjects through the staggered but synchronized exposure approach.
Solution Approach 2:
The system uses periodic pulsed illumination rather than continuous lighting. Each pulse illuminates a specific row group during its exposure window, and the periodic nature of these pulses reduces average power consumption and heat generation compared to continuous illumination required by global shutter 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
Enables sharp, well-exposed images of vehicle occupants even in low light conditions, reducing motion blur and improving image quality for occupant monitoring tasks, such as driver monitoring and gesture detection, while maintaining efficient IR illumination and heat management.
Implementation Method 1
all rows of the image sensor are simultaneously exposed for an exposure time T and with a sensor gain G. At the end of the exposure time T, charge is transferred from each sensor photodiode to a respective capacitor
Implementation Method 2
During the exposure phase, if necessary, a scene being imaged can be illuminated with a light source, for example, an LED flash
Data Source
AI summary
A vehicle occupant monitoring system, OMS, comprises an image acquisition device with a rolling shutter image sensor configured to selectively operate in either: a full-resolution image mode where an image frame corresponding to the full image sensor is provided; or a region of interest, ROI, mode, where an image frame corresponding to a limited portion of the image sensor is provided. An object detector is configured to receive a full-resolution image from the image sensor and to identify a ROI corresponding to an object of interest within the image. A controller is configured to obtain an image corresponding to the ROI from the image sensor operating in ROI mode, the image having an exposure time long enough for all rows of the ROI to be illuminated by a common pulse of light from at least one infra-red light source and short enough to limit motion blur within the image.