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Understanding Vectorization: Converting Raster Images to Vector Graphics

This document explores the process of vectorization, which transforms raster images into vector graphics, including points, lines, curves, and polygons. Highlighting the advantages of vector graphics—such as being compact, scalable, editable, and easy to animate—the text discusses various methodologies, including optimized gradient meshes and Bezier patches for image representation. Furthermore, it presents optimization techniques for achieving high-quality rendering and discusses the research interests of Jian Sun in the field of visual computing.

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Understanding Vectorization: Converting Raster Images to Vector Graphics

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Presentation Transcript

  1. Image Vectorization Cai Qingzhong 2007/11/01

  2. What is Vectorization?

  3. Image Vectorization • Goal • convert a raster image into a vector graphics • vector graphics include • points • lines • curves • polygons • …

  4. Why Vector Graphics • Compact • Scalable • Editable • Easy to animate

  5. Compact input raster image 37.5KB optimized gradient mesh 7.7KB

  6. Why Vector Graphics • Compact • Scalable • Editable • Easy to animate

  7. Scalable original image vector form bicubic interpolation

  8. Why Vector Graphics • Compact • Scalable • Editable • Easy to animate

  9. Editable

  10. Why Vector Graphics • Compact • Scalable • Editable • Easy to animate

  11. Easy to animate

  12. Related Work • Cartoon drawing vectorization • skeletonization, tracing and approximation • Triangulation-based Method • Object-based Vectorization • Bezier patch • subdivision

  13. Image Vectorization using Optimized Gradient Meshes Jian Sun, Lin Liang, Fang Wen, Heung-Yeung Shum Siggraph 2007

  14. About the author --- Jian Sun • Lead Researcher, Visual Computing Group, Microsoft Research Asia • Research interests in • stereo matching • interactive computer vision • computational photography

  15. Surface Representation • A tensor product patch is defined as • Bezier bicubic, rational biquadratic, B-splines… • control points lying outside the surface

  16. Ferguson Patch

  17. Gradient Mesh • Control Point Attributes: • 2D position • geometry derivatives • RGB color • color derivatives

  18. Flow Chart Original Initial Mesh Optimized Mesh Final Rendering

  19. Mesh Initialization

  20. Mesh Initialization • Decompose image into sub-objects • Divide the boundary into four segments • Fitting segments by cubic Bezier splines • Refine the mesh-lines • evenly distributed • interactive placement

  21. Mesh Optimization input image final rendering initial rendering

  22. Mesh Optimization • To minimize the energy function P: number of patches

  23. Levenberg-Marquardt algorithm • Most widely used algorithm for Nonlinear Least Squares Minimization. • First proposed by Levenberg, then improved by Marquardt • A blend of Gradient descent and Gauss-Newton iteration

  24. Smoothness

  25. Smoothness Constraint • Add a smoothness term into the energy which minimizes the second-order finite difference.

  26. Vector line guided optimized gradient mesh

  27. Vector line guided optimized gradient mesh • Given vector fields Vu and Vv, we optimize

  28. More Results

  29. More Results

  30. THE END. Thank you!

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