Provided are a method and device for processing a holographic image. The method includes generating a complex array by performing frequency conversion of input image data on a pixel-by-pixel basis, encoding per-pixel amplitude information and per-pixel phase information represented by complex numbers included in the complex array into real number values, sorting the real number values of the per-pixel amplitudes according to a magnitude and setting a prescribed-order number from among the real number values of the per-pixel amplitudes to a reference value, and normalizing the real number values of the per-pixel amplitudes based on the reference value.