Holographic systems

A method of generating an image holographically comprises displaying a hologram on a first spatial light modulator (SLM) that has a plurality of light modulating pixels (502, fig.5a); illuminating the first SLM, SLM1, with a beam of coherent light to generate an illumination pattern by diffracting the beam of coherent light; displaying, on a second SLM, SLM2 that has a plurality of light modulating pixels, an intensity image comprising a spatial pattern of intensity modulation; illuminating the second SLM with the illumination pattern; and modulating the illumination pattern with the intensity image to project the image. An apparatus for generating an image holographically is also disclosed that includes a hologram data generator 202 coupled to the first SLM and a controller 202 coupled to the second SLM that is arranged to cause the second SLM to display the intensity image. Also disclosed is replacing one or more of the light modulating pixels with one or more light sensing pixels (504, fig.5a) to sense an intensity of said beam of coherent light to determine an intensity of the generated image.