In practice, the presentation of the Image involves the search for an equation that will approximate a beautiful but ineffable psychic adventure. This much pound made clear when he described the process of composing "In a Station of the Metro."
. . . .
The moment of delightful psychic experience and the subsequent search for the precise equation could not be more clearly described. In some way, the poem can be interpreted by means of the definitions in "A Few Don’ts by an Imagiste": the complex is presented "instantaneously," the transition from the Metro station to the wet bough somewhere outside liberates us from "space limits," and the transition from the present faces to the remembered petals breaks down "time limits." But the "Don’ts" don’t account for one peculiarly powerful word in the poem - "apparitions." This word veils the faces in mystery, for it suggests that they are not a mere visual impression but a vision of beauty appearing to the poet from another realm. "Apparition" links "Metro" with the aesthetic of The Spirit of Romance.
The second line of the haiku "super-poses" a concrete image which gives a sensory equation for the rare perception. The heart of the poem lies neither in the apparition nor in the petals, but in the mental process which leaps from one to the other. "In a poem of this sort," as Pound explained, "one is trying to record the precise instant when a thing outward and objective transforms itself, or darts into a thing inward and subjective." This darting takes place between the first and second lines. In the simplest possible verbal equation (a=b), the adventure lies in the unstated relation between the elements. The factors exist for the sake of the equivalence, the images for the sake of the Image. As Stanley Coffman puts it, "the images are so arranged that the pattern becomes an Image, an organic structure giving a force and pleasure that are greater than and different from the images alone."
From The Poetry of Ezra Pound: Forms and Renewals, 1908-1920. Copyright © 1969 by The University of California Press.