Calibration of the optical trigonometric relationships in structured light is essential for the accuracy of out-of-plane displacement measurement. A simple calibration mechanism based on real-time image subtraction is proposed. Details of calibrating the height-to-phase ratio of the digital fringe projection method, the relationship between out-of-plane and in-plane displacements of the digital projection-speckle correlation method, and the scale factor of the optical system are described. The calibration methods are applied to the deformation measurement of a clamped Plexiglas plate, which demonstrates the effectiveness of the calibration methods. The real-time subtraction-based calibration methods provide alternatives for calibrating structured light techniques used for out-of-plane displacement measurement.