Spatial Frequency Imaging for Fruit Bruise Detection
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Solution Overview
Problem
Current machine vision systems in the fruit industry struggle to accurately detect bruises in apples due to their reliance on simple reflectance geometry, which fails to distinguish between scattering and absorption effects, limiting their ability to provide a detailed, quantitative assessment of fruit condition and spatial variability.
Innovation Solution
The implementation of Spatial-Frequency-Domain Imaging (SFDI) for non-invasive, quantitative determination of spatially resolved absorption and reduced scattering coefficients over a wide field-of-view, enabling depth sectioned imaging and simultaneous fluorophore spectral characterization, which separates average background optical properties from heterogeneity components and assesses depth sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If simple reflectance geometry is used in machine vision systems, then the system complexity is reduced, but the ability to distinguish between scattering and absorption effects deteriorates
Solution Approach 1:
The patent segments the measurement process into multiple spatial frequencies of illumination patterns. By projecting sinusoidal patterns at different spatial frequencies and analyzing the modulated reflectance at each frequency, the system can separately determine absorption and scattering coefficients. This segmentation of the measurement into frequency components resolves the contradiction by enabling precise optical property discrimination without requiring complex hardware modifications.
Solution Approach 2:
The patent introduces spatial frequency as an additional dimension to the measurement. Instead of using simple reflectance geometry, the system modulates the illumination in the spatial domain and analyzes the reflected light's spatial frequency content. This dimensional transformation enables the system to extract both absorption and scattering information from what would otherwise be a single integrated measurement, resolving the contradiction between simplicity and measurement precision.
2Device complexity
If single point measurement techniques are used, then the device complexity is reduced, but the ability to characterize volume spatial variability deteriorates
Solution Approach 1:
The patent creates a measurement system that serves multiple functions simultaneously. The wide-field spatially modulated illumination system can determine absorption coefficients, scattering coefficients, and their spatial distributions across the entire fruit surface in a single measurement setup. This multi-functionality resolves the contradiction by providing comprehensive spatial variability characterization without requiring multiple separate measurement devices or procedures.
Solution Approach 2:
The patent transitions from single-point measurements to wide-field spatially-resolved measurements by introducing spatial frequency modulation across the entire field of view. The system captures reflectance information at multiple spatial locations simultaneously and resolves the spatial distribution of optical properties through Fourier analysis of the modulated patterns. This dimensional expansion enables comprehensive spatial variability assessment while maintaining relatively simple device architecture.
3Productivity
If wide-field imaging is implemented, then the productivity is improved, but the measurement precision of optical properties deteriorates
Solution Approach 1:
The patent segments the wide-field measurement into multiple spatial frequency components. By projecting and analyzing sinusoidal patterns at different spatial frequencies across the wide field of view, the system can quantitatively determine absorption and scattering coefficients at each spatial location. This frequency-domain segmentation enables precise optical property measurement while maintaining wide-field coverage and high productivity.
Solution Approach 2:
The patent replaces traditional mechanical scanning or point-by-point measurement approaches with a optical field-based measurement system. By using spatially modulated illumination and capturing the reflected patterns with a camera, the system achieves wide-field quantitative measurement in a single shot, eliminating the need for mechanical movement and enabling high-speed inspection without sacrificing measurement precision.
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
SFDI allows for rapid, wide-field quantitative mapping of optical properties, effectively detecting bruising and quantifying its severity by distinguishing between bruised and non-bruised regions based on scattering coefficient differences, providing a comprehensive assessment of fruit condition without physical contact.
Implementation Method 1
Light penetration in multiple scattering media such as fruit, both scattering and absorption contribute to the distance-dependent attenuation
Implementation Method 2
Light absorption is related to chemical components in fruit, including chlorophyll, sugar, and water
Implementation Method 3
encoding periodic pattern of illumination preferably with a fluorescent excitation wavelength when exposing a turbid medium to the periodic pattern to provide depth-resolved discrimination of structures within the turbid medium
Data Source
AI summary
A method and an apparatus for noninvasively and quantitatively determining spatially resolved absorption and reduced scattering coefficients over a wide field-of-view of a food object, including fruit or produce, uses spatial-frequency-domain imaging (SFDI). A single modulated imaging platform is employed. It includes a broadband light source, a digital micromirror optically coupled to the light source to control a modulated light pattern directed onto the food object at a plurality of selected spatial frequencies, a multispectral camera for taking a spectral image of a reflected modulated light pattern from the food object, a spectrally variable filter optically coupled between the food object and the multispectral camera to select a discrete number of wavelengths for image capture, and a computer coupled to the digital micromirror, camera and variable filter to enable acquisition of the reflected modulated light pattern at the selected spatial frequencies.