System and Methods for Shape Measurement Using Dual Frequency Fringe Patterns

Abstract

A method obtains the shape of a target by projecting and recording images of dual frequency fringe patterns. Locations in each projector image plane are encoded into the patterns and projected onto die target while images are recorded. The resulting images show the patterns superimposed onto the target. The images are decoded to recover relative phase values for the patterns primary and dual frequencies. The relative phases are unwrapped into absolute phases and converted back to projector image plane locations. The relation between camera pixels and decoded projector locations is saved as a correspondence image representing the measured shape of the target. Correspondence images with a geometric triangulation method create a 3D model of the target. Dual frequency hinge patterns have a low frequency embedded into a high frequency sinusoidal, both frequencies are recovered in closed form by the decoding method, thus, enabling direct phase unwrapping.

What is claimed is: 
     
         1 . A method for measuring shapes comprising the steps of:
 encoding light source coordinates of a scene using dual frequency sinusoidal fringe patterns;   modulating the light source with the dual frequency sinusoidal fringe patterns; and   recording images of the scene while the scene is being illuminated by the modulated light source.   
     
     
         2 . A method as recited in  claim 1 , further comprising the step of extracting coded coordinates from the recorded images by using a closed form decoding algorithm. 
     
     
         3 . A system for three-dimensional shape measurement comprising:
 a light source for projecting such fringe patterns onto a scene;   a camera for recording images of the scene under illumination; and   a system for processing the recorded images including: a first module for encoding light source coordinates using dual frequency sinusoidal fringe patterns; a second module for extracting the encoded coordinates from the recorded images; and a third module for computing the scene shape using a geometric triangulation method.   
     
     
         4 . A system as recited in  claim 3 , further comprising a turntable, wherein the scene is an object on top of the turntable, the light source projects fringe patterns and the camera records images of the object at different rotations of the turntable while keeping the object fixed on top the turntable,
 the second module decodes all recorded images, and   the third module computes a shape of the object from all captured turntable rotations and generates a 3D model of the object.   
     
     
         5 . A method for obtaining a shape of a target object comprising the steps of:
 projecting dual frequency fringe patterns on the target object;   recording images of the illuminated target object;   encoding locations in each projector image plane into the projected dual frequency fringe patterns while images are recorded;   decoding the images to recover relative phase values for the projected dual frequency fringe patterns primary and dual frequencies;   unwrapping the relative phase values into absolute phases;   converted the absolute phases back to projector image plane locations; and   creating a correspondence image based on a relation between camera pixels and decoded projector locations, wherein the correspondence image represents a measured shape of the target object.   
     
     
         6 . A method as recited in  claim 5 , further comprising the step of creating a 3D model of the target object based on the correspondence images together with a geometric triangulation of the target object. 
     
     
         7 . A method as recited in  claim 5 , further comprising the step of using direct phase unwrapping.