Rotatable Polarization Element for Image Contrast Enhancement
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Solution Overview
Problem
Current image contrast enhancement techniques, such as SWIR imaging and software algorithms, face limitations due to high costs, limited integration time, and reduced dynamic range of SWIR cameras, as well as the inability to effectively improve saturated images.
Innovation Solution
A polarization-aided image contrast enhancement system that includes a rotatable polarization element and a computing system to control its orientation, allowing for the selective removal of polarized sky photons and enhancement of image contrast by maximizing the signal-to-noise ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If SWIR imaging is used to reduce Rayleigh scattering from the sky, then image contrast is improved, but the cost increases significantly and dynamic range is reduced
Solution Approach 1:
The patent extracts and removes polarized sky light from the optical path using a rotatable polarization element. By selectively blocking the polarized component of sky light while allowing non-polarized light from objects to pass through, the system reduces sky brightness without requiring SWIR imaging, thus avoiding the associated cost and dynamic range limitations.
Solution Approach 2:
The patent changes the polarization state parameter of the sky light by rotating the polarization element to different orientations. This dynamic adjustment of the polarization filter angle allows the system to adaptively control the amount of polarized sky light blocked, optimizing image contrast while maintaining visible light imaging capabilities.
2Illumination intensity
If SWIR imaging is used to reduce sky scattering, then image contrast is improved, but integration time is limited due to shallower well depths
Solution Approach 1:
By removing polarized sky light through the polarization element, the system reduces the total photon count from the sky background. This extraction of harmful polarized photons allows the detector to integrate longer without saturating, as the remaining non-polarized light from objects of interest does not cause premature well depth exhaustion.
3Illumination intensity
If software contrast improvement techniques are used, then image contrast is enhanced, but saturated images cannot be improved
Solution Approach 1:
The patent applies preliminary action by blocking polarized sky light before it reaches the detector and before the image is captured. This pre-prevention of sky light saturation allows the detector to operate within its dynamic range, producing unsaturated images that can then be processed by software algorithms for contrast enhancement.
Solution Approach 2:
By extracting and removing the polarized component of sky light at the optical element level, the system prevents saturation from occurring in the first place. This physical removal of the problematic light component before detection ensures that all captured images remain within the detector's linear range, making subsequent software processing effective.
4Illumination intensity
If a rotatable polarization element is added to the optical path, then image contrast is improved, but device complexity increases
Solution Approach 1:
The patent employs a rotatable polarization element that can dynamically adjust its orientation to match the changing polarization angle of sky light throughout the day. This dynamic adaptation allows a single optical component to perform optimally across different times and conditions, reducing the need for multiple fixed filters or complex switching mechanisms.
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
The system achieves improved image contrast and longer integration times by physically removing saturating photons, thereby enhancing the signal-to-noise ratio and enabling the detection of fainter objects, particularly in visible light, NIR, and SWIR imaging.
Implementation Method 1
a rotatable polarization element configured to receive light from one or more mirrors of a telescope and located in an optical path between the one or more mirrors of the telescope and the photodetector
Data Source
AI summary
Polarization-aided image contrast enhancement is disclosed. A rotatable polarizing element (e.g., a linear polarizer, waveplate and static polarization analyzer, etc.) may be inserted in front of an imaging camera (e.g., between the optics and camera of a telescope) to suppress a significant amount of polarized background sky brightness due to sunlight scattered by aerosols and gas particles in the sky and enhance imaging contrast of the field. This may be accomplished by installing a linear polarizer into a motorized rotation stage. As the polarizer rotates in the stage, transmitted sky brightness will vary sinusoidally with polarizer orientation. At any point in the sky and at any time, there will exist a polarizer orientation that minimizes transmitted sky intensity and maximizes contrast in the image.