Hierarchical Volumetric Fusion of Depth Images

Transcription

1 Hierarchical Volumetric Fusion of Depth Images László Szirmay-Kalos, Milán Magdics Balázs Tóth, Tamás Umenhoffer

2 Real-time color & 3D information Affordable integrated depth and color cameras

3 Application: 3D scanning

4 Application: limitations of compositing Chroma keying Augmented reality Compositing can be based on color: Fixed order No shadows No reflections, refractions, cross illumination

5 Deph compositing (Zinemath) Zinemath - ZLense

6 3D reconstruction of a point i *x * R i y i *z j*x j*y j*z k *x * ky k *z f (xc,yc,zc) p w Rpc t t (xi,yi) xi = fxc/zc xi =(X-cx)sx yi = fyc/zc yi =(Y-cy)sy (cx(c,cxy,) cy) f ( X cx )sx p w R f (Y c y ) s y zc t d( X, Y ) zc t 1 Back projection zc (X,Y)

7 3D point cloud

8 Point cloud Fusion Projection Object Dynamic camera, static scene Problems: in different images the camera changes camera tracking based on static objects in different frames different points are visible We need to maintain surface information between points Solution (Curless/Levoy): Scene is represented by an emerging distance field

9 3D reconstruction input Depth image: distance of the visible surface in each pixel Noisy and unreliable

10 Surface reconstruction Curless-Levoy algorithm Truncated Signed Distance Field (TSDF) d d(x,y,z) voxel

11 Aims Reconstruct static scenes with moving camera Real-time reconstruction GPU-based implementation Fast camera tracking Common methods (SIFT, SURF etc.) are slow Efficient, high resolution TSDF storage To reconstruct fine geometric details GPU memory is limited

12 Proposed method Two-level, hierarchical TSDF Observation: usually most of the scanned 3D space is empty Iterative reconstruction algorithm Measured depth image Camera tracking Camera pose Depths and normal vectors Macrocell refinement Distance generation 3D mesh, etc. Macrocell marking Divided cells Applications Intersected macro-cells TSDF Distance fusion

13 Hierarchical TSDF Micro-cell store Decomposed macro-cell Empty list Macro-cell array Empty macro-cell Micro cell block 8 8 8

14 Macro-cell marking visible surface not affected intersected empty Tru nca tion dist anc e macro-cells

15 Macro-cell marking: gather-style Wasteful! Project each voxel to the depth map and compare depth macro-cells

16 Scatter-style marking (but still faster) visible surface not affected intersected Visit affected voxels by ray-casting empty Tru nca tion DD A ste ps dist anc e macro-cells

17 Avoiding atomic operations Macro-cell marking Determine empty and intersected cells Without synchronization! Empty counter is intersected 20 0 Index to the block of child micro-cells is empty

18 Fusion Distance fusion Only for the previously marked micro-cells

19 Rendering Distance map generation Hierarchical DDA Different step size in the macro and micro cells ray

20 Camera tracking Iterative Closest Point (ICP) q1 Projective matching q2 R, t E (R, t ) qn p1 p2 pn 1 p i R q i t min n i Back projection of current depth Zero-crossings of the TSDF

21 Results Kinect2 depth camera NVIDIA 690GTX GPU Real-time reconstruction 1mm cell resolution

22 Results With the same memory usage: 8mm vs 1mm cell size Kinect Fusion Proposed method

23 Thank you!

24 Time of flight depth sensors Pulsed modulation: Accurate time measurement expensive Continuous modulation Periodic distance