Techniques for extracting phase data of off-axis interferogram images are disclosed. At least one sample-related interferogram image associated with a sample is spectrally decomposed to obtain a set of frequency components thereof, and a portion of the set of frequency components is used to generate at least one complex image having a reduced size being smaller in size than the sample-related interferogram image and being indicative of the phase data of the at least one sample-related interferogram image. The reduced size complex image is then used to generate a phase image of the least one sample-related interferogram image.