A study on spectral analysis combining with image processing for lightness correction in spherical fruits by using hyperspectral imaging

作者:Zhang, Baohua; Li, Jiangbo; Huang, Wenqian; Wang, Chaopeng; Zhao, Chunjiang; Liu, Chenlianq; Huang, Danfenq
来源:American Society of Agricultural and Biological Engineers Annual International Meeting 2015, China,Jiangxi,Fuzhou,Lean, 2015-07-26 to 2015-07-29.

摘要

Automatic detection of common defects in spherical fruits by using vision systems is still not available due to the high variability of fruit surface color and the uneven distribution of lightness on spherical fruits. This paper presents a novel lightness correction method for spherical fruits by using hyperspectral imaging system combined with spectral analysis and image processing methods. Images at 725 nm were selected by analyzing the full spectra of sound and defective ROIs for lightness correction. Images at 925 nm were selected for mask image obtaining, and minimum circumscribed circle (MCC) extraction. Then the individual ideal lightness model of each spherical fruits was constructed automatically adaptive to the size, boundary shape, and position of the inspected fruit according to the lightness distribution on standard spherical object. According to the fact that similar influence (lightness) in each of the correspond pixels and wavelengths caused by geometrical shape (Lambertian surface) are always similar, the final lightness correction method was developed based on the ratio between monochromatic image and ideal lightness model of the inspected spherical fruits. Three popular spherical fruits, apple, peach and citrus, were selected for performance validation of the proposed lightness correction. The lightness correction results show that the uneven lightness distribution (especially the uneven lightness on the edge region) on the spherical fruit was significantly eliminated by our proposed method. Though our method was developed based on the spherical fruits, it is still efficient for lightness correction of other approximately spherical food and agricultural products.

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