Phase measurements require the measurement of interferogram intensities. In this paper it is investigated how the validity of the evaluated phase is affected by the averaging of the interferogram intensities across the pixels of a CCD-array. In our previous works it has been shown numerically that the validity of the phase values depends on the topology of the speckle field. Here, it is examined analytically how the topology influences the phase evaluation with respect to averaging. One result is that in certain cases the absolute value of the phase gradient can be determined solely from the intensity of the speckle field, without any reference beam. Based on this result the phase error at intensity maxima, saddle points and for stationary points of the phase is examined.© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.