A grading system based on image processing techniques was developed fo
r automatic inspection and grading of flue-cured tobacco leaves. The s
ystem used machine vision in extraction and analysis of color, size, s
hape, surface texture and vein. A two-dimensional feature space was pr
oposed to express feature distribution of tobacco leaves. The space wa
s found to be well confined in an elliptic region. A database was cons
tructed to record the feature distribution of standard contrast tobacc
o leaves prepared by experts through visual evaluation. The decision o
n grades was made based on the so-called 'nearest-neighbor' method for
which the overall difference among features between the measured toba
cco leaves and the standard contrast samples were used as a target par
ameter for judgment. This system can be easily trained by users with t
he knowledge of the feature distribution information of different toba
cco leaves. It can also be adapted for the inspection of other agricul
tural products.