Dynamic three-dimensional shape measurement for specular freeform surfaces with the quaternary orthogonal grid fringes

Abstract

Deflectometry is a promising method for freeform surfaces due to its wide applications and ease of implementation, but it is not robust against environmental noise and vibrations. A new deflectometry method using the quaternary orthogonal grid fringes is proposed to retrieve the surface slopes. Combined with a classic N-step phase-shifting technique, only one image is required to extract the two perpendicular directional phases instead of two groups of phase shifted fringes. The color of each pixel can be encoded by red, green and blue components. In each color component, two perpendicular fringe patterns compose quaternary orthogonal grid fringes. In practice, the relative shift between different colors is set depending on the lateral resolution of the camera lens and the zoom relation of the object-image. The object-image relationship can be established by using only one distorted colorful orthogonal fringe pattern reflected via the surface. This process is fast and stable because the RGB codes of every block are significantly different to its neighbor in at least one color component. This method is suitable for dynamic measurement of specular objects, and the influence of varying environment and moving objects can then be eliminated.