1. A method for determining the surface profile of an object, comprising the steps of: directing at said object an incident beam of light having a sinusoidally varying intensity pattern; modulating the phase of the sinusoidal intensity pattern of said incident beam; receiving at a detector a deformed grating image of the object for a number of different modulated phases of said incident beam; determining, for points on the surface of the object, the height at each said point with respect to a reference plane, each said height determination including the step of combining image intensity values, for said different modulated phases of the incident beam, at a detector position corresponding to a respective point of the object.