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Phase-shifting digital holography is a technique for phase measurement with high spatial resolution and applied to many
fields. This technique typically requires four phase-shifted interferograms between a signal beam and a reference beam.
We focused on the two-step phase shifting algorithm, which needs only two phase-shifted interferograms and an
intensity distribution of the reference beam to reduce the number of required interferograms. However, in this algorithm,
the intensity of the reference beam must be much greater than that of the signal beam because this algorithm uses the
quadratic formula and the inside of square root must be positive. This leads to the saturation of the dynamic range of the
image sensor and the degradation of accuracy. In this paper, we propose a virtual interferogram-generation algorithm
(VIGA) to improve the performance of phase-shifting digital holography only using two interferograms. This algorithm
virtually generates a π phase-shifted interferogram by the intensity distribution of the signal beam and that of the
reference beam with an observed interferogram. Therefore, capturing two real interferograms and generating two virtual
interferograms, the four-step phase shifting algorithm can be used for this method. Comparing to the conventional
algorithm, the VIGA has no limitation in terms of the magnitude of the intensity. This means that the intensity of the
reference beam and that of the signal beam can be equalized and the dynamic range saturation of the image sensors can
be prevented. Therefore, the VIGA makes highly accurate phase measurement possible owing to the effective utilization
of the dynamic range of the image sensors.
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