Infrared Camera Flat Field Correction Using Temperature-Dependent Scale Factors
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Solution Overview
Problem
Current thermal imaging systems face challenges in calibrating focal plane arrays (FPAs) due to non-uniform responses among infrared detectors, which are exacerbated by variations in physical characteristics and out-of-field infrared radiation from mechanical components, leading to degraded thermal image quality.
Innovation Solution
The system calibrates infrared cameras by determining flat field correction values and supplemental flat field correction values, which are applied to thermal image data to correct for non-uniformities along the optical path, with scale factors adjusted based on temperature and temperature changes of camera components, allowing for real-time correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If a shutter is inserted into the optical path close to the FPA to reduce shutter size and provide a compact infrared camera, then the device compactness is improved, but the ability to correct for out-of-field infrared radiation from other optical path components is worsened
Solution Approach 1:
The patent divides the optical path into two distinct segments: the segment between the shutter and FPA (corrected by traditional shutter calibration) and the segment from the scene through lenses and windows to the shutter (uncorrected by traditional calibration). By separately characterizing and correcting each segment, the system achieves comprehensive correction while maintaining a compact design with the shutter close to the FPA.
Solution Approach 2:
The patent extends the calibration approach from a single-point correction (at the shutter location) to a multi-dimensional correction that accounts for the entire optical path. This is achieved by capturing flat field images with the shutter in different positions and using these to generate correction values that compensate for non-uniformities across the complete optical path, effectively adding a spatial dimension to the calibration process.
2Measurement precision
If traditional shutter calibration is used to correct for non-uniformities between the shutter and FPA, then the calibration for that specific path is improved, but the correction for out-of-field infrared radiation from lenses, windows, and mounting hardware is worsened
Solution Approach 1:
The patent performs preliminary characterization of the entire optical path by capturing flat field images with the shutter in known positions before actual thermal imaging. These preliminary measurements are used to generate flat field correction values that pre-compensate for non-uniformities from all optical path components, including lenses, windows, and mounting hardware, so that these harmful factors are corrected before they affect the final thermal images.
Solution Approach 2:
The patent uses flat field correction values as an intermediary mechanism to transfer and apply correction information across the entire optical path. These correction values act as a mediator that translates the characterized non-uniformities from flat field measurements into compensatory adjustments that can be applied to thermal image data, effectively eliminating the harmful out-of-field infrared radiation effects.
3Measurement precision
If flat field correction values are determined for both the shutter path and external scene path, then the comprehensive correction capability is improved, but the device complexity and calibration process complexity are worsened
Solution Approach 1:
The patent creates a universal calibration framework where flat field correction values serve multiple functions: they correct for FPA detector non-uniformities, compensate for out-of-field infrared radiation from all optical path components, and can be applied to both shutter-based and scene-based imaging. This multi-functional approach consolidates what would otherwise require separate calibration systems into a single unified process.
Solution Approach 2:
The system performs self-calibration by using its own internal components (the shutter and FPA) to generate the correction data needed. By capturing flat field images through the existing optical path and processing these images to extract correction values, the system serves its own calibration needs without requiring external calibration equipment or additional hardware, thereby reducing overall system complexity.
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 significantly improves the uniformity and accuracy of thermal images by accounting for non-uniformities across the entire optical path, reducing radiometric distortion and enhancing the signal-to-noise ratio.
Implementation Method 1
Focal plane arrays (FPAs) which detect infrared radiation are well known in the art and are used by infrared cameras to provide thermal images. For example, infrared radiation passing through an optical path of the infrared camera is received by infrared detectors of the FPA
Implementation Method 2
The FPA may be calibrated over one or more levels of photon flux by inserting a shutter (i.e., an optical obscuration also referred to as a calibration flag) into the optical path of the infrared camera. The temperature of the shutter may be adjusted to emulate a thermal black body detected by the FPA
Implementation Method 3
The quality of thermal images provided by FPAs may be degraded due to non-uniform responses among the individual infrared detectors to incident infrared radiation. Infrared detectors of an infrared camera may be calibrated to determine flat field correction (FFC) values, which may be used to correct for non-uniformities associated with optical paths of the infrared camera
Implementation Method 4
FPA performance may also be degraded by non-uniform out-of-field infrared radiation from surrounding mechanical components. Supplemental flat field correction (SFFC or supplemental FFC) values are also determined and applied to thermal image data to further correct for such non-uniformities
Implementation Method 5
In some aspects, a scale factor may be applied to the supplemental FFC values to adjust the supplemental FFC values based on a temperature and/or rate of temperature change of the infrared camera and/or components thereof (e.g., focal plane arrays, lenses, housing, etc.)
Data Source
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AI summary
Various techniques are provided to perform flat field correction (FFC) for infrared cameras. In one example, a system includes a focal plane array (FPA) of an infrared camera configured to capture thermal image data in response to infrared radiation received by the FPA via an optical path of the infrared camera. The system further includes a memory configured to store a set of supplemental FFC values. The system further includes a processor configured to determine a scale factor based at least on a temperature and/or a rate of temperature change of an internal component of the infrared camera; generate a scaled set of supplemental FFC values based on the scale factor and set of supplemental FFC values; and apply the scaled set of supplemental FFC values to the thermal image data to adjust for non-uniformities associated with at least a portion of the first optical path.