By means of the phase difference of two phase-contrast images obtained with digital holography, it is possible to measure the topography and/or deformation of macroscopic objects. Owing to the roughness of the object surface this phase-difference images present a high-contrast speckle noise that ruins, the always required, phase-unwrapping process. We present the development and implementation of a phase-shifting like algorithm for filtering phase-difference images. We show that its performance is superior compare to the known approaches, like low-pass and median filters