In a magnetic resonance method and system to automatically differentiate whether a pixel of an MR image acquired with magnetic resonance system originated from fat-dominated tissue or water-dominated tissue, only one spin echo-based magnetic resonance signal per pixel is acquired at a point in time at which the phase of a magnetic resonance signal of aqueous tissue has a phase opposite to the phase of a magnetic resonance signal of fat tissue. The phase angle of the pixel is then calculated, a base phase at the pixel depending on the magnetic resonance system is determined, and a corrected phase angle of the pixel is determined from the phase angle and the base phase. Whether the pixel originated from fat-dominated tissue or water-dominated tissue is then determined using the corrected phase angle of the pixel.