The use of complex amplitude correlation to determine the deformation field for in-plane motions in digital speckle pattern interferometry (DSPI) is investigated. The result is compared to experiments where only DSPI-algorithms, as well as where combined DSPI - intensity correlation are used. Experiments with and without large rigid body motions are studied. An advantage of using complex amplitude correlation instead of intensity correlation is that the phase change describing the deformation is retrieved directly from the correlation peak and there is no need to compensate for the large movement and then use interferometric algorithms to obtain the phase information. A discovered drawback of this method is that the correlation values drops very quick if there is a phase gradient larger than K across the sub image used for the cross correlation. This means that in order to use the complex amplitude correlation the size of the subimages must be proportional to the magnitude of the present deformation gradient. Or, a third parameter in the crosscorrelation algorithm that compensates for the phase variation is needed.