Direct ESPI phase estimating from only two interferograms

One step phase shifting method for Electronic speckle pattern interferometry (ESPI) is an effective way for dynamic phenomenon analysis. But all the present methods need prior processes to get the reference phase field either by the traditional phase shifting method or by the image-sequence analyzing method. This paper presents a direct phase estimating method using only two interferograms, with no need of any prior information. By reasonably assuming that the background, the modulation and the phase changes are constant in local areas, the whole phase change field modulated by π with sign ambiguity can be estimated. Then through analyzing the phase change values, the whole sign field can be determined. With the help of the sign field, the modulation of the phase changes can be removed by phase unwrapping methods. The effectiveness of this method has been proved by real experimental tests.