  A new computational imaging method to reconstruct the complex wave-field is
reported. Due to the existence of zero frequency component, the measured signal
by amplitude modulation of pupil has a spectrum similar to the one of off-axis
hologram. The mathematical analogy between them is established in this paper.
Based on this observation and analyticity of band-limited signal under any
diffraction-limited system, an algorithm from Kramers-Kronig (KK) relations is
utilized to recover the phase information only from the intensity patterns.
From the sensing side, only two measurements are required at least. From the
reconstruction algorithm side, our method is iteration-free and parameter-free,
also without any assumption on sample characteristics. It owns several
advantages over existing phase imaging methods and could provide a unique
perspective to understand current computational imaging methods.
