How does Alfred Tennyson, 1st Baron Tennyson use imagery in The Lady of Shalott?

In Lines 10-18, Tennyson's imagery is that of nature, of freedom, and of movement. This imagery is contrasted with the inflexible, colorless walls and towers of Camelot in line 15. The flowers in the next line are not described by their colors or even by their motion in the breeze, but are "overlooked" by the grey walls, as if they are held prisoner. This tone of severity in the middle of nature's healthy activity prepares the reader for the introduction of the Lady of Shalott in line 18.