Shape measurement by digital speckle temporal sequence correlation with digital light projector

A new method of three-dimensional shape measurement, called digital speckle temporal sequence correlation, is presented. Random digital speckle is projected on the reference plane, which is moved N times in equal depthwise steps. At each step, speckle image is captured by a CCD camera and saved in a computer as the reference-plane set R(t ). Replacing the reference plane with the object, the modulated speckle image O was also captured. The cross correlation between any subimage O(x ,y) in O and the serial subimages R(x ,y ;t ) located at the same position in R(t ) is approximately quadratic. The position of the main peak of the correlation curve is the height of the object point. In order to measure speckle-sets complicated objects, two new methods, called multiple reference-speckle-sets and multiple correlation-peak optimization, are also presented. Experiment proves them very effective. Our method surpasses the limitations of the horizontal correlation in previous methods and is a true temporal sequence correlation method. It is simple in principle and offers higher measurement precision without complicated phase-unwrapping and calibration processes, and can be used to measure discontinuous and spatially isolated shapes.