Abstract: In order to investigate the variation in the warpage of potato slices during hot air drying, in this study we examined the morphological changes of dried potato slices with different diameters (22, 33 and 44 mm) and thicknesses (1, 3 and 5 mm) though 3D point cloud combined with digital image analysis technology. The 3D point cloud data were transformed to a grayscale image with a bit depth of 16. Based on the image characteristics obtained, threshold segmentation, morphological image processing and median filtering were conducted for the removal of outliers and the repairing of holes. Through the pseudocolor contour maps as well as analysis of the mechanism of shrinkage during the drying process, the warpage of potato slices was discussed, revealing that the shrinkage of height went through three steps: regular warping, collapse and crimping deformation. The inflection point for mean height was positively correlated with the thickness but was independent of the diameter. Before the inflection point, the height was highly consistent among individuals, but was obviously different after the inflection point. Then, the rates of change in mean height at the inflection and end points and inter-individual variances were extracted as features for analysis. It was found that both the thickness and diameter had little impact on the rates of change in mean height or inter-individual variances. When the thickness of potato slices was 5 mm, the average rate of change in mean height was ?39.55%. At the end point, the rate of change in mean height and inter-individual variance were positively correlated with the diameter and negatively correlated with the thickness. When the thickness of potato slices was 1 mm and the diameter was 44 mm, the rate of change in mean height and inter-individual variance were 317.38% and 199.34%, respectively. The findings from this study may provide a theoretical basis for future research on intelligent control of the drying process of potato slices.

Key words: hot air drying; potato slices; image processing; warpage; time-varying analysis