Determination and adjustment of optimal defocus level for fringe projection systems

The sinusoidal fringe pattern is widely used in fringe projection profilometry. Too much or too little defocusing will affect the quality of sinusoidal fringe patterns and consequently jeopardize the accuracy of measurement results. This paper proposes a method to quantify and ascertain the defocus level by simulations and experiments. By simulating the defocus pattern with a Gaussian low-pass filter, the optimum defocus level of the fringe pattern is determined so that the projected fringe pattern is closer to the sinusoidal function. Then, a method is proposed to adjust the projector to make the projected pattern in the optimal defocus degree. Experiments show the feasibility and the validity of the proposed method, and the accuracy is improved up to 9.9%, compared with the focus-projected pattern.