Rolling Shutter Infrared Imaging for Background Light Subtraction
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Solution Overview
Problem
Existing IR image capture systems struggle with background light subtraction, particularly in low-light conditions, due to scattering and reflections from strong light sources, which can obscure objects like license plates and road signs, and existing solutions either increase manufacturing costs or fail to handle camera or scene movement effectively.
Innovation Solution
Utilizing a rolling shutter image sensor to capture interleaved IR-illuminated and non-IR-illuminated image frames with modulated IR light, allowing for synchronized background light subtraction even with camera or scene movement, by creating IR-illuminated and non-IR-illuminated images from staggered pixel lines.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If an optical bandpass filter is used to block visible light and only pass IR wavelengths, then background light interference is reduced, but the camera becomes harder to align and focus, and hardware complexity increases
Solution Approach 1:
The patent extracts the visible light component from the captured image by using a second image taken with IR lights off to represent the visible light background. This extracted visible light image is then subtracted from the first image (taken with IR lights on) to remove background light interference without requiring physical filters
Solution Approach 2:
The patent introduces a second image capture as an intermediary step to obtain the visible light background information. This intermediary image serves as a mediator that carries the background light information, which is then used to subtract from the primary IR image to eliminate interference
2Object-affected harmful factors
If the IR lights are switched on for one full frame and then off for the next full frame, then background light can be subtracted, but the system cannot handle camera or scene movement effectively
Solution Approach 1:
The patent segments the image capture process into two interleaved sequences using a rolling shutter sensor: lines captured with IR lights on and lines captured with IR lights off. This segmentation allows the capture to be spread over a longer time period while maintaining the ability to subtract backgrounds, effectively handling movement by distributing the capture across multiple shorter intervals
Solution Approach 2:
The patent implements a dynamic capture strategy where the IR light modulation is synchronized with the rolling shutter line-by-line capture process. The system dynamically adjusts which lines are captured with IR on and which with IR off, allowing adaptation to scene movement while maintaining effective background subtraction
3Speed
If the rolling shutter sensor captures lines interleaved with IR lights changing state, then background light subtraction can handle movement, but the image capture process becomes more complex
Solution Approach 1:
The patent performs preliminary organization of captured lines into two separate sets (IR on and IR off) during the image capture process itself. This preliminary action is done through synchronized control of the IR light modulation with the rolling shutter capture, preparing the data in advance for straightforward background subtraction without requiring complex post-processing
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 effective background light subtraction with reduced noise and improved object visibility, even in dynamic scenes, by optimizing the IR light cycle with the image capture process.
Implementation Method 1
a rolling shutter image sensor with a plurality lines of pixels, wherein the rolling shutter image sensor during capture of an image reads out pixel data from one line of pixels at a time
Implementation Method 2
an IR light source configured to be turned on and off, wherein when being turned on, the IR light is configured to illuminate the scene
Implementation Method 3
subtracting background light from the IR-illuminated image using pixel values in the non-IR-illuminated image, thereby creating a modified IR-illuminated image
Data Source
AI summary
A method of performing background light subtraction in an infra-red (IR) illuminated image depicting a scene, comprises: providing a rolling shutter image sensor; providing an IR light source configured to be turned on and off; changing an on-off status of the IR light source a plurality of times while capturing an image; capturing two or more image frames each image frame comprising: a first set of lines of pixels comprising image data captured with the IR light turned on; a second set of lines of pixels comprising image data captured with the IR light turned off; creating an IR-illuminated image; creating a non-IR-illuminated image; subtracting background light from the IR-illuminated image using pixel values in the non-IR-illuminated image.