We describe a new optical inspection method based on the analysis of the combined space-frequency representation of the scattered field. Samples of the sliding window spectrum are measured optically and then the surface features are reconstructed by numerical methods. The methods investigated include reconstruction from the Gabor expansion coefficients, using the Zak transform, and phase recovery from amplitude only data, using projection onto constraint sets algorithm. Computer simulations and experimental results show that this method can reconstruct accurately shallow phase objects, even when their dimensions are smaller than the diffraction limit of the optical setup. © 1997 Society of Photo-Optical Instrumentation Engineers.