Model of Color Parameters Variation and Correction in Relation to “Time-View” Image Acquisition Effects in Wheat Crop

Florin Sala,Cosmin Alin Popescu,Ciprian Rujescu,Mihai Valentin Herbei

doi:10.3390/su12062470

Florin Sala, Cosmin Alin Popescu + Show 2 more

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https://doi.org/10.3390/su12062470

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Abstract

Many images of agricultural crops are made at different times of the day, images with different spectral information about the same crop in relation to conditions when the picture was taken. A set of 30 digital images of a wheat crop in the BBCH 3-Stem elongation code 32–33 stage was captured between 9 am and 14 (UTC+3), in the 0°–180° variation range of the image acquisition angle on the E-W axis (cardinal directions). A high variation of the spectral data given by the combination of the hour (h) and angle (a) at which the images were captured was found. The interdependence relationship between the analyzed parameters (r, g, and b), and the time (t) and the angle (a) of image acquisition was assessed with the linear correlation coefficient. By calculating the roots of the mathematical expressions of the correlation coefficients dependence on the angles (a) or times of day (t), the optimal angle and time were determined as a combination of the two variables for capturing images and obtaining optimal ro, go, bo values. The correction coefficients of the normalized r, g, and b values obtained out of the optimal field were determined. To this end, the multiplication of the r(a,t), g(a,t), and b(a,t) values with the ρa,t, γa,t, and βa,t correction coefficients was suggested to reach the optimal values for sustainable decisions.

Highlights

The imaging-based techniques for earth’s crust, plant cover, and crop investigation have developed and diversified dramatically
While the crop was uniform, we discovered a certain variation of the color parameters (r, b, and g) relative to the time and angle of image acquisition, following the change of the solar illumination angle in relation to the studied area
This case may occur in real practice, when images are acquired by agricultural machinery in real time, while wheat or other crops are being tended

Summary

Introduction

The imaging-based techniques for earth’s crust, plant cover, and crop investigation have developed and diversified dramatically. The new investigation methods bring more precision to agricultural practice, as they provide real-time information for adequate crop management corresponding to the nutritional status, the flowering structure, the phytosanitary condition, the reaction to various stress factors (hydric, thermal etc.,), the yield estimation and even the interventions required to compensate different deficiency in crops [15,16,17,18,19] Operational environmental factors such as the camera height, the angle to the horizon, and the distance to the target object refer mainly to the image geometry and can be established as being constant, to have a uniform distribution of the absorption and radiation properties of the target area. The use of working methods that provide color stability may reduce the degree of uncertainty that characterizes the assessment of the physiological parameters of plants whose study is based on their color

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