3D Object Measurement Using Encoded Structured Light

Application of Encoded Structured Light in 3D Measurement

Encoded structured light is a technique that reconstructs 3D object morphology by projecting specific light patterns and analyzing their deformation. The core principle involves using a projector to cast encoded structured light patterns (such as stripes, Gray codes, or phase-shifting patterns) onto the target object surface, while a camera captures the deformed patterns. Through image processing and phase demodulation algorithms, the system ultimately recovers the 3D coordinates of the object surface.

### Key Technical Steps

System Calibration Before measurement begins, both camera and projector must undergo calibration to determine their intrinsic parameters (focal length, distortion coefficients) and extrinsic parameters (relative position and orientation). This step directly impacts the accuracy of subsequent 3D reconstruction. In code implementation, this typically involves using calibration patterns and OpenCV functions like calibrateCamera() and stereoCalibrate().

Structured Light Encoding and Projection Common encoding methods include binary coding, phase-shifting method, and hybrid encoding. The phase-shifting method is widely adopted for its high-resolution characteristics - it projects multiple sinusoidal fringe patterns with different phases and calculates surface height information from phase variations. Algorithm implementation requires generating phase-shifted patterns using sine wave functions and managing projection sequence timing.

Image Acquisition and Preprocessing The camera captures modulated fringe patterns deformed by the object surface. Preprocessing steps include noise reduction, contrast enhancement, and fringe center extraction to improve phase calculation accuracy. Code implementation typically involves OpenCV operations like Gaussian blur, histogram equalization, and skeletonization algorithms for centerline extraction.

Phase Demodulation and 3D Reconstruction Phase demodulation algorithms (such as Fourier transform or phase unwrapping) convert deformed fringe patterns into continuous phase information. Combined with calibration parameters, the system maps phase values to 3D coordinates to complete point cloud reconstruction of the object surface. Implementation requires phase calculation using arctangent functions and spatial phase unwrapping algorithms to resolve 2π ambiguities.

### Technical Advantages and Challenges Encoded structured light technology offers non-contact operation, high precision, and efficiency, making it suitable for industrial inspection and reverse engineering applications. However, measurement accuracy can be affected by ambient light, surface reflectivity, and calibration errors. Robustness improvement requires algorithmic optimization (such as adaptive thresholding) and hardware configuration enhancements.