FIGURE 6.

Wheat spikes recognition results. [For nitrogen level mixing model, nitrogen level model, and color feature threshold segmentation model, recognition under different nitrogen level gradient. The left picture was nitrogen level mixing model, the middle picture was nitrogen level model, the right picture was color feature threshold segmentation. N1, N2, N3 and N4 represented 0 (nitrogen-free), 225 kg⋅ha^–1 (1/2 of the normal nitrogen level), 450 kg⋅ha^–1 (normal nitrogen level), and 900 kg⋅ha^–1 (excessive nitrogen level), respectively].