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Removing Highlight Spots in Visual Hull Rendering

Removing Highlight Spots in Visual Hull Rendering. Jie Feng, Liang Chen and Bingfeng Zhou Institute of Computer Science & Technology Peking University, Beijing, China. Visual Hull Rendering. An efficient technique for image-based rendering

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Removing Highlight Spots in Visual Hull Rendering

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  1. Removing Highlight Spotsin Visual Hull Rendering Jie Feng, Liang Chen and Bingfeng Zhou Institute of Computer Science & Technology Peking University, Beijing, China

  2. Visual Hull Rendering • An efficient technique for image-based rendering • The intersection of “viewing cones” constructs a convex hull that contains the object

  3. …… …… Visual Hull Rendering • Suffers from the highlight spots on the images rendered new view reference images

  4. Highlight Spots Removal Methods • Some methods need more than one image at a single position • Increase the difficulty of acquiring and storing source images in visual hull rendering [Agrawal et al., SIGGRAPH 2005]

  5. Highlight Spots Removal Methods • Single-image-based methods • Utilizing image gradient, illumination constrains etc. in image editing • Working well when background is simple or uniformly textured • Cannot guarantee the consistency of different reference images [Pérez et al., SIGGRAPH 2003] [Tan et al., ICCV 2003]

  6. Removing Highlight on VH • Visual hull methods provide great convenience for highlight removal • Reference images usually have much overlaps • The correspondence of pixels in different images could be found target reference image another reference image

  7. Image-based Visual Hull Rendering • Image-based Visual Hull (IBVH) , Matusik et al., 2000. The calculations are limited in image space Main steps to render a new view: • Projecting viewing ray to reference images (epipolar line) • The epipolar line intersects the 2D silhouette • Projecting 2D intervals back to get 3D bounding edges on the viewing ray

  8. Removing Highlight Spots on IBVH • The main steps of our method: • Selecting sub-images in the target image that containing highlight spots • Finding correspondences of pixels in other reference images • Resampling the highlight sub-image from its counterparts

  9. Selecting Highlight Sub-images • Calculations are applied only to sub-images, the rest part remain unchanged • To reduce computing cost and minimize the error introduced by pixel mapping and resampling

  10. Finding Pixel Correspondence • Finding pixel correspondence between reference images is similar to rendering a new view in IBVH, only: • The target image is not a synthesized new view, but one of the reference images • The calculations are limited to the selected highlight sub-images

  11. vbk vb va vak rbk r lk rak pbk ps pk pak p0 Is Ik I0 Ck C0 Finding Pixel Correspondence • The approach

  12. Finding Pixel Correspondence • The counterparts of a highlight sub-image on other reference images reference images target reference image

  13. Highlight Sub-image Resampling • Re-calculating the color of sub-image pixels to reduce highlight effect • Blending the appearance colors of p0 and its corresponding pixels {pk | k=1…n} by their gray level deviations Avg. gray level: Final color: Blending weight:

  14. θs θk ps pk p0 Is Ik I0 Highlight Sub-image Re-sampling • n nearest images are used in blending a pixel, according to the angles between viewing rays (θk) • Larger n helps to filter out highlighted pixels, but also causes blurring effect in complex- textured areas

  15. Highlight Sub-image Re-sampling • Adjusting n according to each sub-image’s complexity (gray level deviation sum) • Using less images in complex-textured sub-image, more in simple-textured sub-images Avg. gray level: Gray level deviation sum: Num. of image in use:

  16. Experimental Results • Fixing a single reference image • 23 reference images in tatol • Nmax=9 (simple texture)Nmin=4 (complex texture)

  17. Experimental Results • Rendering new views without highlight spots original / fixed reference images rendering result

  18. Summary • A simple and efficient method to remove highlight spots in visual hull rendering • Utilizing the calibration information of reference images to find pixel correspondence • Blending corresponding pixels to filter out highlight spots • More realistic and precise result • The re-lighting of visual hull become possible

  19. Thanks! fengjie@icst.pku.edu.cn

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