A method of generating beam-steering drive values from image data for driving a beam-steering spatial light modulator - SLM - in a projection system, said image data indicative of at least one image to be displayed by said projection system, said projection system comprising the beam-steering SLM and an amplitude modulator, the beam-steering SLM being configured to selectively steer light to form an intermediate image on said amplitude modulator, the amplitude modulator being configured to spatially modulate the intermediate image to form a final image, said method comprising: generating a mathematical description of a wavefield corresponding to a desired intermediate image at said amplitude modulator, backward-propagating said wavefield by multiplying the mathematical description by a propagation operator to generate a mathematical description of the wavefield at the beam-steering SLM, low-pass filtering the mathematical description of the wavefield at the beam-steering spatial light modulator to remove amplitude information, forward propagating the low-pass filtered mathematical description of the wavefield by multiplying the low-pass filtered mathematical description by a propagation operator to generate a mathematical description of a new wavefield at the amplitude modulator, said new wavefield being an approximation of the desired intermediate image, if a predetermined termination condition is not met, iterating the backward-propagating to the forward-propagating steps, each time using the new wavefield generated in the forward-propagating step of the last iteration in the backward-propagating step of the following iteration, and if said predetermined termination condition is met, generating the beam-steering drive values, based, at least in part, on the low-pass filtered mathematical description of the wavefield provided in the latest iteration of the low-pass filtering step. generating a mathematical description of a wavefield corresponding to a desired intermediate image at said amplitude modulator, backward-propagating said wavefield by multiplying the mathematical description by a propagation operator to generate a mathematical description of the wavefield at the beam-steering SLM, low-pass filtering the mathematical description of the wavefield at the beam-steering spatial light modulator to remove amplitude information, forward propagating the low-pass filtered mathematical description of the wavefield by multiplying the low-pass filtered mathematical description by a propagation operator to generate a mathematical description of a new wavefield at the amplitude modulator, said new wavefield being an approximation of the desired intermediate image, if a predetermined termination condition is not met, iterating the backward-propagating to the forward-propagating steps, each time using the new wavefield generated in the forward-propagating step of the last iteration in the backward-propagating step of the following iteration, and if said predetermined termination condition is met, generating the beam-steering drive values, based, at least in part, on the low-pass filtered mathematical description of the wavefield provided in the latest iteration of the low-pass filtering step.