The catch is, that the patterns have the resolution of the wavelength of light. You cannot take plain black and white film for this, you would need extremely high resolution film material. Agfa actually produced special film for holograms for a while, high contrast and very high resolution, but with a sensitivity like ISO 10. The resolution is far higher than normal LCD screens offer and that would be the main impediment. The math for calculating the interference patterns is almost trivial, but the scale is massive. Doing it in real-time would still require quite high-power setups, as you would have to calculate hundreds of rays per "pixel".
