Table 1.

Key of imaging techniques and applications purpose.

Imaging system	Description	Phenotypic trait parameters	Application purpose
Visible light	The visible light imaging technique is camera sensitive and produces gray or color scale images.	Image-based projected biomass, dynamic growth, color, shape descriptors, root architecture, seed morphology, panicle traits, etc.	This imaging technique can be used to assess plant growth status, biomass accumulation, nutritional status, or health status (Golzarian et al., 2011; Camargo et al., 2014; Yang et al., 2014).
Thermal infrared	Thermal infrared imaging sensor includes near-infrared, multispectral line scanning cameras. This imaging technique produces time series or single-time-point analysis based data.	Leaf area index, shoot or leaf temperature, surface temperature, insect infestation of grain, leaf and canopy water status, composition parameters for seeds, disease severity, etc.	This imaging technique used to characterize the plant temperature responses to the water status and transpiration rate and detect difference in stomatal conductance of the plant for adoption abiotic stress (Chen et al., 2014b).
Fluorescence	Fluorescence imaging technique detects chlorophyll and other fluorophores signals using fluorescence cameras.	Photosynthetic performance, quantum yield, non-photochemical quenching, leaf disease severity assessments, leaf health status, etc.	It provides a fleet way to probe photosystem status in vivo, diagnosing early stress responses before decline growth (Fiorani and Schurr, 2013), useful for disease detection in genetic disease resistance (Chen et al., 2014b), mapping QTLs for growth-related traits (El-Lithy et al., 2004), characterizing mutants with numerous photosynthetic pigment compositions (Niyogi et al., 1998), etc.
Hyperspectral	This imaging technique use hyper spectral, thermal cameras produced continuous, or discrete spectra raw data.	Water content, leaf growth and health status, panicle health status, grain quality, pigment composition, etc.	This imaging technique used to measure spatiotemporal growth patterns during the experiment and provide insight into the diversity of growth dynamics (Chen et al., 2014b).
CT	It is based on X-ray digital radiography/computed tomography.	Grain quality, tiller, morphometric parameters, water content, flow velocity, etc.	This imaging is widely used to asses tissue density (Aerts et al., 2014), measuring tiller numbers (Yang et al., 2014), grain quality, etc.
PET	Positron emission tomography.	Water transport, flow velocity, etc.	This is used to visualize distribution and transportation of radionuclide-labeled tracers involved in metabolism-related activities (Jahnke et al., 2009; Granier and Vile, 2014).
MRI	Magnetic resonance imaging.	Water content, morphometric parameters, etc.	The purpose of this imaging technique is to visualize metabolites, provides structural information, and monitor internal physiological processes occurring in vivo (Borisjuk et al., 2012; Granier and Vile, 2014).