A method of generating a binary computer generated hologram for use in displaying a holographic image, the method comprising the steps of generating a complex modulation computer generated hologram corresponding to a desired reply object, transforming the complex modulation computer generated hologram into a real positive computer generated hologram, and transforming the real positive computer generated hologram into a binary computer generated hologram by comparing each element of the real positive computer generated hologram with at least one neighboring element and replacing the compared element with a binary value which depends upon the result of the comparison.