I am trying to visualize images from Xray experiments. I am using MATLAB for phase-contrast data and I have to apply a phase retrieval algorithm in order to get the phase of the radiography. The problem is that every algorithm I have found in the literature demands an initial guess of what the image is showing and I cannot find something good enough(because I don't know exactly what I am expecting). Is there a way to somehow determine the initial guess for the phase retrieval algorithm?