A processing scheme able to obtain any arbitrary intragrating strain distribution of a fiber Bragg grating (FBG) is proposed and demonstrated. The processing method employs just the intensity of the FBG reflection spectrum to obtain its deformation profile by combining a geometrical processing scheme with the particle swarm optimization technique. The technique has been evaluated using several spectra generated from very heterogeneous strain distributions and with a real spectrum obtained from a 5 mm length FBG under an asymmetric perturbation. The achieved results exhibit a good spatial resolution (Δ≈0.5 mm) and repeatability.