To resolve the error in processing fringe images with heavy noise, light fluctuation and low contrast in non-contact measurement based on conoscopic holography, the measurand can be computed from its relation with the phase of a fringe. A method for scanning in selection region is presented on the analysis of common methods’ shortage. It is used to pick up numbers of fringes and the phase of less than one fringe, and it connects the fringe projection with the gradient center of mass to count the numbers of extreme points of the light fringe and start points of less than one fringe which needs fitting by the cosine function. Experimental results show that this method can reduce effects of fringe curvature, backup and light fluctuation. So measurement velocity and precision can be improved correspondingly.
