Atom interferometers typically use the total populations the interferometer's output ports as the signal, but finer spatial structure can contain useful information. We pattern a matter-wave phase profile onto an atomic sample. An interferometer translates the phase into a measurable pattern in the atomic density that we use perform the first direct precision measurement of the 7 Li tune-out wavelength near 671 nm. Expressed as a detuning from the |2S 1/2 , F =2 →|2P 1/2 , F =2 transition, we find 3329.3(1.4) MHz for the tensor-shifted tune out of the |2S 1/2 , F =2, mF =0 state with σ ± light polarization and 3310.1(4.9) MHz for the tune out of the the scalar polarizability. This technique may be generalized for directly sensing spatially varying phase profiles.