Method and apparatus for acquiring reference grating of three-dimensional measurement system using moire

An apparatus of acquiring a reference grating of a three-dimensional measurement system using moiré, wherein the three-dimensional measurement system comprises a light source for emitting light, a projection grating for generating a grating pattern, a grating actuator for moving the projection grating and a camera for acquiring the reference grating and a moiré pattern obtained from an object, and analyzes the moiré pattern acquired through the camera to measure the shape of the object, the apparatus comprising:

• a noise detector for detecting whether or not the acquired reference grating includes noise and removing the noise when the reference grating includes the noise to correct the reference grating;
• and
• a controller for controlling the grating actuator to move the projection grating in order to acquire the next reference grating when the noise detector does not detect noise from the reference grating, correct the reference grating according to the noise detector and then move the projection grating when the reference grating includes noise,
• wherein the noise detector includes an image analysis algorithm configured to:
• binarize the acquired reference grating;
• thin the reference grating such that central points of lines of the binarized reference grating are detected and portions of the lines other than the central points are eliminated to leave only the central points;
• substitute the central points to a linear equation to obtain optimum straight lines that closely pass through the central points;
• calculate the slope of the reference grating using the straight lines;
• and
• obtain a distance between neighboring straight lines corresponding to central lines of the grating and generating a grating using the distance.