Presented by Dr. Yujia Zhang
Examples:
laser scanner
kinect
-depth from focus ,depth from stereo
Concept :active vision
Passive triangulation:Stereo Vision
Active Triangulation:Structured Light 结构光
- one of cameras replaced by light emitter
- correspondence solved by searching in camera image
- no geometric constraints
Structured light
- any spatio-temporal pattern of light projected on a surface
Classification of structured light patterns
time multiplexing
- high resolution
- robust
- only reconstruct static object
- need large num of patterns
Binary Codes for time multiplexing: $2^n$ strips
N-ary Codes: decrease num of pattern but increased the basis of code and intensity(grey levels/colors)
spatial multiplexing
- using spatial infos
- but can produce errors in decoding process
- maximum res cannot be reached
Non-formal codification:periodic pattern
De brujin sequences: order m over an alphabet of n symbols in a circular string of length $n^m$ that contains every substring of length m exactly once
M-arrays: like de brujin but using sequence matrix can use grey/color level
Direct Codification: Reduced pattern ,high res,but noisy and non-linearities low accuracy can use grey/color level
High accu ,High res -> phase shift+gray code
High accu ,
Structured light 3d scanning
Stereo Calibration
Pattern Encoding and Decoding
single-axis encoding
double-axis encoding
Coding Methods
Binary code $N=log_2(\frac{w}{h})$
GrayCode $B_iB_{i-1} \oplus G_i$
Maximum min-Sw gray code:
Phase shifting Methods
Micro phase shifting: Decode $R_{micro} = M_{micro} \cdot U_{micro}$
Triangulation: ray-ray intersection method to get depth
2D circular phase shifting
- intensity calibration of projector to get gamma response work
- ray-cone triangulation- using normal alg will get wrong result
- 44 patterns only for static object
- for reflection object it can do better job
Hybrid Coding Methods
- gray+phase shifting
- Min-SW + Micro phase Shifting
- Maximum Min-SW Gray Code and Circular phase shifting
Real Time tracking
ArUco tracker
co-registration system
IMU-assisted ArUCo marker tracking