Dual-wavelength holography has better axial range than single-wavelength holography, allowing unambiguous phase imaging but at the expense of increased noise. We have studied error reduction in dual wavelength holography using a modified fine map. The fine map is successful in measurement and has shown error reduction when the height of the object is less than the appled wavelength, but is unstable when the step height is larger than that wavelength. We have modified the fine map and we have found that the modified fine map was successful in measurement and error reduction even though the height of object was larger than the wavelength.