Multispectral Camera Sensing for Ambient Illumination Characterization
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Solution Overview
Problem
Existing methods for correcting the effect of colored ambient illumination on camera images are under-constrained and impractical, such as assuming a scene averages to grey or using a spectrometer, which are cumbersome or fail in certain conditions.
Innovation Solution
A camera system with a multispectral sensor and flash unit captures spectra with and without flash to determine a scene's flash spectrum, compensates for flash illumination, and estimates the ambient illumination spectrum for color correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a spectrometer is used to directly measure the spectrum of ambient illumination, then measurement precision is improved, but device complexity and cost increase significantly
Solution Approach 1:
The patent uses a multispectral sensor to capture spectral information as a simplified copy of what a full spectrometer would measure. Instead of directly measuring the ambient illumination spectrum with complex equipment, the system captures reflected light spectra from the scene which contain embedded spectral information about the illumination source.
Solution Approach 2:
The patent introduces scene reflectance as an intermediary element. By measuring how different materials in the scene reflect light at various wavelengths, the system indirectly derives information about the ambient illumination spectrum without directly measuring it, thus avoiding the need for complex spectrometer hardware.
2Measurement precision
If manual selection of ambient illumination type is requested from the user, then measurement precision may be improved, but ease of operation deteriorates
Solution Approach 1:
The system performs automatic illumination spectrum estimation without requiring user intervention. The multispectral sensor captures spectral data and the processing system automatically analyzes this data to characterize the ambient illumination, eliminating the need for manual user selection while maintaining accuracy.
Solution Approach 2:
The system uses spectral feedback from the multispectral sensor to automatically adapt to different illumination conditions. By continuously analyzing the captured spectral information, the system can identify and compensate for various lighting conditions without user input, creating a closed-loop automatic adaptation mechanism.
3Illumination intensity
If flash illumination is used to illuminate the scene, then illumination intensity is improved, but color accuracy deteriorates due to colored ambient illumination effects
Solution Approach 1:
The patent changes the spectral parameters of the illumination by using flash lighting, which provides intense broadband illumination. This allows the system to overcome low-light conditions while the multispectral sensor captures the resulting spectral information to later compensate for any color casts from ambient illumination.
Solution Approach 2:
The patent extracts the ambient illumination spectrum information from the spectral measurements taken under flash illumination. By analyzing the differences between captured spectra and known flash characteristics, the system isolates and removes the effects of colored ambient illumination to recover accurate scene colors.
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
Accurately reconstructs the scene's reflectance spectrum and ambient illumination, enabling effective color correction and classification, suitable for consumer devices like smartphones and projectors.
Implementation Method 1
a multispectral sensor to capture a spectrum of light from the scene in a plurality of wavelength channels
Implementation Method 2
an illuminator, e.g. a camera flash unit, to provide illumination of the scene
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
A camera system with a multispectral sensor that can be used in combination with a flash to determine a spectrum of the ambient illumination without needing a separate measurement. This may then be used to colour-correct an image captured with or without flash.