Noncontact and Wide-Field Characterization of the Absorption and Scattering Properties of Apple Fruit Using Spatial-Frequency Domain Imaging

Abstract

Spatial-frequency domain imaging (SFDI), as a noncontact, low-cost and wide-field optical imaging technique, offers great potential for agro-product safety and quality assessment through optical absorption (μa) and scattering (μ) property measurements. In this study, a laboratory-based SFDI system was constructed and developed for optical property measurement of fruits and vegetables. The system utilized a digital light projector to generate structured, periodic light patterns and illuminate test samples. The diffuse reflected light was captured by a charge coupled device (CCD) camera with the resolution of 1280 × 960 pixels. Three wavelengths (460, 527, and 630 nm) were selected for image acquisition using bandpass filters in the system. The μa and μ were calculated in a region of interest (ROI, 200 × 300 pixels) via nonlinear least-square fitting. Performance of the system was demonstrated through optical property measurement of ‘Redstar’ apples. Results showed that the system was able to acquire spatial-frequency domain images for demodulation and calculation of the μa and μ. The calculated μa of apple tissue experiencing internal browning (IB) were much higher than healthy apple tissue, indicating that the SFDI technique had potential for IB tissue characterization.

Applications of compressive sensing in spatial frequency domain imaging

“…Additional data reduction methods have been previously applied in the form of pixel binning. 23 Such pixel binning method could also be applied in conjunction with the CS algorithms used within this work, although maintaining original single-pixel values for reconstructions preserves the resolution and contrast of the original images, validating the contribution of CS for data reduction purposes as compared to other methodologies.…”

Spatial frequency domain imaging in 2019: principles, applications, and perspectives

“…As an example, multiple groups are using SFDI to characterize produce and identify subsurface bruising in apples and pears as a quality control tool. 133,134 This makes SFDI a versatile tool that can be customized by a number of research groups.…”

Non-destructive, non-invasive, in-line real-time phase-based reflectance for quality monitoring of fruit

“…Therefore, the major component of the reflected light is diffused. The diffused reflectance R d (x) is expressed as (Hu et al, 2016):…”

“…where the constant A depends on the refractive index of the sample, ′ = is the effective attenuation coefficient. µ a is the absorption coefficient and ′ m s is the reduced scattering coefficient (Hu et al, 2016). The diffused reflectance is, thus, determined by the scattering observed by the incident light.…”