Gloss measurements of raw agricultural products using image analysis

Abstract

Gloss is considered one of the most important visual attributes of many foods, which is difficult to measure objectively. In this paper, a gloss imaging system (GIS) was implemented to evaluate the suitability of four indexes for measuring gloss from intensity images in flat and curved surfaces and to analyze gloss of some fruits and vegetables. Three indexes were computed from goniometric curves: maximum intensity (MI), width of the curve at 50% (WC), and area under the curve (AC). The fourth index was computed from the same intensity images as the average of the reflected luminance flux (LF) at the surface of the image. The results showed linear relationships (R-2 = 0.97) when values of MI, AC, LF for flat and curved gloss targets in the range of 4-90 units of gloss (GU) were compared with their standard gloss levels. However, the measured gloss was significantly affected by curvature and unevenness of the surface of fruits and vegetables. In spite of this, we concluded that a colour digital camera of moderate cost combined with simple image analysis procedure can yield parameters which correlate highly with the gloss appearance of fruits and vegetables and allow measurements over a very wide range of gloss with high sensitivity. (C) 2009 Elsevier Ltd. All rights reserved.