Click on “Download PDF” for the PDF version or on the title for the HTML version.

If you are not an ASABE member or if your employer has not arranged for access to the full-text, Click here for options.

Because the images of bruises often exhibit patterns and intensity values similar to the stem-end/calyx, it is important to discriminate the bruises from the stem-end/calyx in an apple sorting system. To solve this problem, a push-broom hyperspectral imaging system was developed to acquire reflectance images of apple between 400 nm and 1100 nm. A total of 60 apples were used, 30 of them were sound, 15 of them with bruises near the calyx, and 15 of them with bruises near the stem-end. The full wavelength region from 450 to 980 nm was segmented into the visible region 450 to 780 nm and the near-infrared region from 780 to 980 nm. Then the principal component analysis (PCA) was conducted on the full region and the two segmented regions respectively. The PC images were used to detect the bruise and the effective wavebands were selected according to the PC images loading plots. The PC images from 450 to 780 nm could not be used to detect the bruises. The PCA was used again on the effective wavebands selected from 780 to 980 nm and 450 to 980 nm. Results show that the effective wavebands from 780 to 980 nm could be used to discriminate bruises from stem-end and calyx. None of the healthy apple was misclassified. None of the bruises were misclassified as stem-end or calyx. 93.3% of the bruises near the stem-end were correctly classified, and only 86.7% of the bruises near the calyx were correctly classified using the PC images resulted from the effective wavebands 820 and 970nm. The classification error of the bruises near the stem-end/calyx would be caused by the strong light spot on the sample. Moreover, the only 2 effective wavebands 820 and 970 nm from the NIR region would decrease the cost to establish a multispectral imaging system.