Submitted to: Laser Focus World
Publication Type: Trade journal
Publication Acceptance Date: 2/22/2005
Publication Date: 4/30/2005
Citation: Lu, R., Peng, Y. 2005. Multispectral scattering measures fruit texture. Laser Focus World. April Issue. p. 99-1003. Interpretive Summary:
Technical Abstract: Firmness is an important quality parameter in grading many horticultural products such as apples, cucumbers, pears, peaches, and watermelons. The majority of past research on nondestructive firmness measurement has been focused on mechanical methods such as quasi-static force/deformation, vibration, impact, and acoustics. This article describes a new technique of using multispectral scattering to measure fruit firmness. A liquid crystal tunable filter (LCTF) based multispectral imaging system is assembled to acquire spectral scattering images from apple fruit. Scattering images are collected from individual apple fruit at 10 nm interval between 650 nm and 1000 nm. A four-parameter Lorentzian function is proposed to describe scattering profiles for individual wavelengths. Lorentzian function parameters are then linearly related to fruit firmness. A set of optimal wavelengths is found, using the cross validation method, for Golden Delicious and Red Delicious apples. For Golden Delicious, 8 wavelengths are needed to obtain best firmness predictions whereas for Red Delicious 7 wavelengths are sufficient. The firmness prediction models are able to predict fruit firmness with r=0.82 and 0.81, respectively, for Red Delicious and Golden Delicious, which are comparable to or better than many nondestructive mechanical methods. The LCTF based multispectral imaging system provides an effective means to determine optimal wavelengths for measuring fruit firmness.