Image reconstruction is based on phase retrieval by combining incomplete Fourier-space magnitude data with real-space information. Phase retrieval is performed based on the Fourier-space magnitude data, where the real-space information is expressed in a form suitable to use as a phase retrieval constraint, preferably using a wavelet-space representation. The use of incomplete Fourier-space magnitude data advantageously reduces the amount of data required compared to approaches that need comprehensive Fourier-space magnitude data. The real space information can be regarded as partial information of the image being reconstructed. Depending on the application, more or less real space information may be available.