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An improved rotation-invariant thinning algorithm

An improved rotation-invariant thinning algorithm. Peter I. Rockett Department of Electronic & Electrical Engineering, University of Sheffield, Mappin Street 2005 IEEE(TPAMI ). Reporter : Mao- Hua Cheng. Outline. 1. Introduction

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An improved rotation-invariant thinning algorithm

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  1. An improved rotation-invariant thinning algorithm Peter I. Rockett Department of Electronic & Electrical Engineering, University of Sheffield, Mappin Street2005 IEEE(TPAMI) Reporter : Mao-Hua Cheng

  2. Outline • 1.Introduction • 2. Descriptionrule of the Ahmed-Ward (A-W) thinning algorithm • 3. Description of the modified algorithm • 4. Results • 5. Discussion and conclusion

  3. 1. Introduction • Image Skeletonization promises to be a powerful complexity-cutting tool for under • compact shape description • pattern recognition • robot vision • Animation • petrography pore space fluid flow • model/analysis of bone/lung/circulation • Image compression for telemedicine

  4. 1. Introduction • A Improved the origin of the shortcoming of the A-W algorithm • A-W algorithm fails on two-pixel wide lines • Improve to produce a smother

  5. 2. Descriptionrule of the Ahmed-Ward (A-W) thinning algorithm • a rule-based system for thinning • Any pattern of the 3×3 neighborhood can only fall under one of the following 20 rules • ex. This pixel should not be deleted

  6. 2. Descriptionrule of the Ahmed-Ward (A-W) thinning algorithm • Advantage • corrects this shortcoming based on graph connectivity • Disadvantage • Create fails on two-pixel wide lines

  7. 3. Description of the modified algorithm • modified algorithm comprises two stages： • First, we apply the 20 rules of Ahmed and Ward over the 8-neighbors of each pixel • applied iteratively where the pixels are marked for deletion • The secondprocessing stage takes the provisional skeleton from the first processing stage

  8. 3. Description of the modified algorithm • Second stage： • we extend their notation to label the central pixel as x0

  9. 3. Description of the modified algorithm • Example of construction of an undirected connectivity graph Table 1 Adjacency Matrix for the Graph original pixel configuration Resultingundirected connectivity graph

  10. 3. Description of the modified algorithm • Example of shows a pixel cannot be removed as evidenced by the fact that vertex x2 will become disconnected original pixel configuration Resultingundirected connectivity graph • constructing and searching the adjacency matrix is fast and efficient

  11. 4. Results Comparison of the Numbers of Pixels in the Skeletons of the Chinese Characters

  12. 4. Results

  13. 5. Discussion and conclusion • This second stage uses a graph-based method of determining whether a pixel in a two-pixel wide line can be deleted without disrupting the connectivity of the skeleton • the new algorithm appears to effect far less aggressive erosion of the ends of lines

  14. 5. Discussion and conclusion • Modified algorithm makes greater use of diagonal connectivities to produce a smoother skeleton

  15. Q&A

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