Discrimination of Fresh Tobacco Leaves with Different Maturity Levels by Near-Infrared (NIR) Spectroscopy and Deep Learning

Table 1

The characteristics of fresh tobacco leaves in five maturity levels.

Maturity levels	Characteristics description of fresh tobacco leaf
Unripe	Leaf color is dark green without any yellow, the main vein and branches are all green, and pubescence is not fallen off.
Mature	Leaf color is light green with litter yellow, about 2/3 main vein turns white, and the branches are green with a small amount of pubescence shedding.
Ripe	Leaf color is yellow-green, the main vein is all white, about 1/3 branches turn white, pubescence partly falls off, and the leaf tip is slightly hung down.
Mellow	Leaf color is yellow, the main vein is all white and bright, about 2/3 branches turn white, pubescence is basically or mostly shed off, the leaf surface is covered with macula, the leaf tip and leaf edge turn white, slightly withered, and the leaf tip is scorched and hooked down.
Overmature	The main vein and branches are all white and bright, and leaf color is yellow-white. Most of pubescence fall off, the leaf ear is yellow with withered sharp and scorched edge.