A method for synthesis of driving RF signal, corresponding to sampled hologram, which allows to minimize the capacity of the display memory, is suggested. With the application of new method required frame-buffer capacity for the current displays can be reduced by the factor 1.8 - 3. We have considered three variants of hologram sampling method for data reduction. It is found that minimum hologram data redundancy can be achieved with Fourier and Image types of holographic stereograms. For given 3-D image resolution a maximum image size, which can be displayed without redundancy is determined as 4...5 cm. Further scaling of the image requires application of the sampling method. With proper improvement of the hardware, application of hologram sampling method provides stable capacity of the display memory a little over 32 MB regardless of the image size. Since the method also permits direct synthesis of driving RF signal, acousto-optical modulators with up to several GHz bandwidth can be employed in electroholographic display.