Advisor ：林惠勇 老師 Reporter ：林正祐

1. Variable Baseline/Resolution Stereo David Gallup1, Jan-Michael Frahm1, PhilipposMordohai2, Marc Pollefeys1,3 1University of North Carolina, 2University of Pennsylvania, 3ETH Zurich CVPR’08 Advisor：林惠勇 老師 Reporter：林正祐 8/27/2009

2. Outline • Introduction • Algorithm • Analysis • Accuracy and Time Complexity • Experimental Results

3. Introduction • Multi-baseline、multi-resolution method • To compute depth map which has following properties： • Depth accuracy is “constant” over volume reconstruction. • Angle of triangulation is constant w.r.t depth. • Main ideas • Selecting baseline and focal length proportionally to z, canceling the quadratic term of z and leaving error constant w.r.t depth.

4. Algorithm

5. Accuracy & Time Complexity • Stereo is expected to deliver depth measurements with error < εz, for all z ≦ zfar • Following analyze the effect of baseline & focal length Correspondence error, 1 Geometric resolution (baseline, focal length, depth)

6. Fixed Baseline Stereo • Adjust accuracy by varying focal length, f Use f to describe resolution Huge time complexity

7. Fixed Resolution Stereo • Adjust accuracy by varying baseline, b • Drawback：near range is lost • It can’t rely on increasing the baseline alone.

8. Variable Baseline and Resolution (1/2) • Avoid Znear > Zfar • Avoid near range lost • wide baseline → far range • narrow baseline → near range β can be chosen to give a certain angle of triangulation at Zfar • f α Zfar • b α Zfar • resolution α Zfar2

9. Variable Baseline and Resolution (2/2) • Time complexity • Sum the number of pixel comparisons needed at each depth z steps improvement

10. Experimental Results (1/3)

11. Experimental Results (2/3) • Outdoor scene (1024x768, lateral motion capturing at 30Hz)

12. Experimental Results (3/3) • Outdoor scene (10 megapixel)