SWIR Structured Light 3D Imaging for Vehicle Occupancy
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Solution Overview
Problem
Current systems for determining the number of occupants in a motor vehicle, especially in HOV/HOT lanes, face challenges due to limitations in capturing accurate 3D images through windshields using single-band infrared cameras, which lack depth information and are affected by extrinsic factors like illumination and material reflectance.
Innovation Solution
A system combining a structured illumination source in the short wave infrared (SWIR) wavelength range with near-infrared (NIR) detection capabilities, using a phosphor-coated converter to shift light to a CCD detectable range, allowing for 3D image construction and accurate occupancy determination by analyzing pixel distortions caused by 3D surface variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single-band infrared cameras are used for occupancy detection, then cost is reduced and simplicity is improved, but depth information is lost and measurement precision deteriorates
Solution Approach 1:
The patent transitions from 2D imaging to 3D imaging by introducing structured light projection. The structured light patterns (lines, grids, or dots) are projected onto the target scene, and the distortion of these patterns is used to calculate depth information. This adds a third dimension (depth) to the traditional 2D image capture, enabling accurate 3D reconstruction without requiring multiple cameras or complex hardware configurations.
Solution Approach 2:
The patent introduces structured light as an intermediary element between the camera and the target object. By projecting known light patterns onto the scene and analyzing how these patterns deform when reflected from surfaces at different depths, the system can infer 3D information. The structured light acts as a mediator that carries depth encoding information from the scene to the camera sensor.
2Ease of manufacture
If NIR wavelengths are used for imaging, then detection cost is reduced using CCD detectors, but transmission through glass deteriorates
Solution Approach 1:
The patent changes the wavelength parameter of the structured light from traditional visible or NIR ranges to SWIR (short-wave infrared, 1000-2500 nm). SWIR wavelengths have superior transmission properties through glass compared to NIR, while still being detectable by modified or specialized detectors. This parameter change resolves the contradiction by finding a wavelength range that optimizes both glass transmission and detector availability.
Solution Approach 2:
The patent employs composite detection approaches that may combine SWIR-optimized detectors with NIR-capable detectors in a multi-spectral system. By using multiple detector types with different spectral sensitivities, the system can simultaneously capture SWIR information (for good glass transmission) and NIR information (for cost-effective detection), creating a composite sensing solution that leverages the strengths of both detector types.
3Measurement precision
If SWIR structured light is used for 3D imaging, then depth information and occupancy accuracy are improved, but device complexity increases
Solution Approach 1:
The patent designs the imaging system to serve multiple functions: it can perform both 2D imaging (for basic occupancy detection) and 3D imaging (for precise depth measurement and occupancy verification). The same hardware platform (camera, light source, processor) is configured to execute different imaging modes, making the system universal and adaptable to various enforcement scenarios without requiring completely separate systems for different functions.
Solution Approach 2:
The structured light projection system uses the reflection of projected light patterns from targets at different depths to automatically encode depth information. The system essentially measures itself by analyzing how the projected patterns deform upon reflection, eliminating the need for separate depth sensors or complex calibration procedures. The light patterns carry their own depth encoding information through their deformation characteristics.
4Loss of information
If visible light properties are used for occupancy detection, then intrinsic features are captured, but extrinsic factors like illumination and reflectance affect reliability
Solution Approach 1:
The patent uses periodic or modulated structured light patterns (such as alternating line patterns, rotating grids, or time-varying dot patterns) to illuminate the scene. By projecting patterns that change over time in a known sequence, the system can distinguish between reflected structured light and ambient extrinsic light sources. The periodic modulation allows the detector to identify and measure only the light carrying depth information, filtering out constant or random extrinsic illumination and reflectance variations.
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 accuracy of vehicle occupancy determination by providing a 3D image, overcoming the limitations of single-band infrared systems and offering high transmission through glass, while being less obstructive to the driver, and is cost-effective due to the use of Si-based CCD detectors.
Implementation Method 1
A structured pattern is created by projecting structured light through a customized optical element comprising a patterned grid. Wavelengths of the received pattern are converted to a CCD detectable range using, for example, a phosphor coated converter which shift the received light to a Silicon-based CCD detectable wavelength band
Implementation Method 2
The shifted light comprises an image in a structured pattern of reflected source light
Data Source
AI summary
What is disclosed is a method which combines structured illumination in the SWIR wavelength range with the detection capabilities of NIR to generate a 3D image of a scene for accurate vehicle occupancy determination. In one embodiment, structured light is projected through a customized optical element comprising a patterned grid. Wavelengths of the received structured pattern are shifted to a CCD detectable range. The shifted light comprises an image in a structured pattern. The wavelength-shifted light is detected using an infrared detector operating in the NIR. For each pixel in the detected patterned image, an amount of distortion caused by 3D surface variation at this pixel location is determined. The distortion is converted to a depth value. The process repeats for all pixels. A 3D image is constructed using each pixel's depth value. The number of occupants in the vehicle is determined from the constructed 3D image.