Image Correction and In Situ Spectral Calibration for Low-Cost, Smartphone Hyperspectral Imaging

Matthew Davies,Andrew J S Mcgonigle,Mary B Stuart,Matthew J Hobbs,Jon R Willmott

doi:10.3390/rs14051152

Matthew Davies, Andrew J S Mcgonigle + Show 3 more

Open Access

https://doi.org/10.3390/rs14051152

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Journal: Remote Sensing	Publication Date: Feb 25, 2022
Citations: 8	License type: CC BY 4.0

Affiliation: University of Sheffield

Abstract

Developments in the portability of low-cost hyperspectral imaging instruments translate to significant benefits to agricultural industries and environmental monitoring applications. These advances can be further explicated by removing the need for complex post-processing and calibration. We propose a method for substantially increasing the utility of portable hyperspectral imaging. Vertical and horizontal spatial distortions introduced into images by ‘operator shake’ are corrected by an in-scene reference card with two spatial references. In situ light-source-independent spectral calibration is performed. This is achieved by a comparison of the ground-truth spectral reflectance of an in-scene red–green–blue target to the uncalibrated output of the hyperspectral data. Finally, bias introduced into the hyperspectral images due to the non-flat spectral output of the illumination is removed. This allows for low-skilled operation of a truly handheld, low-cost hyperspectral imager for agriculture, environmental monitoring, or other visible hyperspectral imaging applications.

Highlights

Hyperspectral imaging has risen to prominence in recent years due to its growing role in sensing applications in agriculture and environmental [1–4] monitoring, civil engineering [5,6] and medical applications such as cancer and Alzheimer’s detection [7,8].It is suited to these applications because it comprises additional information that is contained within a hyperspectral image
The corrected image shows how effective the spatial correction algorithm canand be, spatial resolution, they significantly increase the cost of the system, reducing the even when supplied with images heavily affected by operator shake
A method for spatially correcting for operator shake and performing in situ spectral calibration in handheld hyperspectral imaging has been reported alongside a demonstration of its application withing the field of fruit quality assessment

Summary

Introduction

Hyperspectral imaging has risen to prominence in recent years due to its growing role in sensing applications in agriculture and environmental [1–4] monitoring, civil engineering [5,6] and medical applications such as cancer and Alzheimer’s detection [7,8].It is suited to these applications because it comprises additional information that is contained within a hyperspectral image. A specific example used in this work to demonstrate the advantage of defect detection and quality assurance in fruit afforded by hyperspectral imaging over conventional monitoring techniques is well documented in the literature. It is shown not as a novel application but to illustrate the utility of the technique we propose in this work. Each image corresponds to a narrow band of wavelengths (typically 1–10 nm full width half maximum (FWHM) [9,10]) and each pixel value is the wavelength-integrated radiance across that band This allows features to be detected in a reflection spectrum that are otherwise lost in traditional imaging techniques. This is applied to aerial monitoring of large ground areas, disease detection in plants and to aid the segmentation of cells in microscopy [11–13]

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