object detection
play

Object Detection Sanja Fidler CSC420: Intro to Image Understanding - PowerPoint PPT Presentation

Object Detection Sanja Fidler CSC420: Intro to Image Understanding 1 / 48 Object Detection The goal of object detection is to localize objects in an image and tell their class Localization: place a tight bounding box around object Most


  1. Object Detection Sanja Fidler CSC420: Intro to Image Understanding 1 / 48

  2. Object Detection The goal of object detection is to localize objects in an image and tell their class Localization: place a tight bounding box around object Most approaches find only objects of one or a few specific classes, e.g. car or cow Sanja Fidler CSC420: Intro to Image Understanding 2 / 48

  3. Type of Approaches Di ff erent approaches tackle detection di ff erently. They can roughly be categorized into three main types: Find interest points , followed by Hough voting Sanja Fidler CSC420: Intro to Image Understanding 3 / 48

  4. Interest Point Based Approaches Compute interest points (e.g., Harris corner detector is a popular choice) Vote for where the object could be given the content around interest points Sanja Fidler CSC420: Intro to Image Understanding 4 / 48

  5. Interest Point Based Approaches Compute interest points (e.g., Harris corner detector is a popular choice) Vote for where the object could be given the content around interest points Sanja Fidler CSC420: Intro to Image Understanding 4 / 48

  6. Interest Point Based Approaches Compute interest points (e.g., Harris corner detector is a popular choice) Vote for where the object could be given the content around interest points Sanja Fidler CSC420: Intro to Image Understanding 4 / 48

  7. Interest Point Based Approaches Compute interest points (e.g., Harris corner detector is a popular choice) Vote for where the object could be given the content around interest points Sanja Fidler CSC420: Intro to Image Understanding 4 / 48

  8. Interest Point Based Approaches Compute interest points (e.g., Harris corner detector is a popular choice) Vote for where the object could be given the content around interest points Sanja Fidler CSC420: Intro to Image Understanding 4 / 48

  9. Type of Approaches Di ff erent approaches tackle detection di ff erently. They can roughly be categorized into three main types: Find interest points , followed by Hough voting Sliding windows : “slide” a box around image and classify each image crop inside a box (contains object or not?) Sanja Fidler CSC420: Intro to Image Understanding 5 / 48

  10. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.1 confidence [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  11. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” -0.2 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  12. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” -0.1 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  13. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.1 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  14. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” . . . 1.5 . . . [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  15. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.5 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  16. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.4 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  17. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.3 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  18. Sliding Window Approaches Slide window and ask a classifier: “Is sheep in window or not?” 0.1 confidence- 0.2 -0.1 0.1 . . . 1.5 . . . 0.5 0.4 0.3 [Slide: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 6 / 48

  19. Type of Approaches Di ff erent approaches tackle detection di ff erently. They can roughly be categorized into three main types: Find interest points , followed by Hough voting Sliding windows : “slide” a box around image and classify each image crop inside a box (contains object or not?) Generate region (object) proposals , and classify each region Sanja Fidler CSC420: Intro to Image Understanding 7 / 48

  20. Region Proposal Based Approaches Group pixels into object-like regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  21. Region Proposal Based Approaches Group pixels into object-like regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  22. Region Proposal Based Approaches Group pixels into object-like regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  23. Region Proposal Based Approaches Generate many di ff erent regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  24. Region Proposal Based Approaches Generate many di ff erent regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  25. Region Proposal Based Approaches Generate many di ff erent regions Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  26. Region Proposal Based Approaches The hope is that at least a few will cover real objects Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  27. Region Proposal Based Approaches The hope is that at least a few will cover real objects Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  28. Region Proposal Based Approaches Select a region Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  29. Region Proposal Based Approaches Crop out an image patch around it, throw to classifier (e.g., Neural Net) Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  30. Region Proposal Based Approaches Do this for every region Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  31. Region Proposal Based Approaches Do this for every region Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  32. Region Proposal Based Approaches Do this for every region Sanja Fidler CSC420: Intro to Image Understanding 8 / 48

  33. Type of Approaches Di ff erent approaches tackle detection di ff erently. They can roughly be categorized into three main types: Find interest points , followed by Hough voting ← Let’s first look at one example method for this Sliding windows : “slide” a box around image and classify each image crop inside a box (contains object or not?) Generate region (object) proposals , and classify each region Sanja Fidler CSC420: Intro to Image Understanding 9 / 48

  34. Object Detection via Hough Voting: Implicit Shape Model B. Leibe, A. Leonardis, B. Schiele Robust Object Detection with Interleaved Categorization and Segmentation IJCV, 2008 Paper: http://www.vision.rwth-aachen.de/publications/pdf/leibe-interleaved-ijcv07final.pdf Sanja Fidler CSC420: Intro to Image Understanding 10 / 48

  35. Start with Simple: Line Detection How can I find lines in this image? [Source: K. Grauman] Sanja Fidler CSC420: Intro to Image Understanding 11 / 48

  36. Hough Transform Idea: Voting (Hough Transform) Voting is a general technique where we let the features vote for all models that are compatible with it. Cycle through features, cast votes for model parameters. Look for model parameters that receive a lot of votes. [Source: K. Grauman] Sanja Fidler CSC420: Intro to Image Understanding 12 / 48

  37. Hough Transform: Line Detection Hough space: parameter space Connection between image ( x , y ) and Hough ( m , b ) spaces A line in the image corresponds to a point in Hough space What does a point ( x 0 , y 0 ) in the image space map to in Hough space? [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 13 / 48

  38. Hough Transform: Line Detection Hough space: parameter space Connection between image ( x , y ) and Hough ( m , b ) spaces A line in the image corresponds to a point in Hough space A point in image space votes for all the lines that go through this point. This votes are a line in the Hough space. [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 14 / 48

  39. Hough Transform: Line Detection Hough space: parameter space Two points: Each point corresponds to a line in the Hough space A point where these two lines meet defines a line in the image! [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 15 / 48

  40. Hough Transform: Line Detection Hough space: parameter space Vote with each image point Find peaks in Hough space. Each peak is a line in the image. [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 16 / 48

  41. Hough Transform: Line Detection Issues with usual ( m , b ) parameter space: undefined for vertical lines A better representation is a polar representation of lines [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 17 / 48

  42. Example Hough Transform With the parameterization x cos θ + y sin θ = d Points in picture represent sinusoids in parameter space Points in parameter space represent lines in picture Example 0 . 6 x + 0 . 4 y = 2 . 4, Sinusoids intersect at d = 2 . 4, θ = 0 . 9273 [Source: M. Kazhdan, slide credit: R. Urtasun] Sanja Fidler CSC420: Intro to Image Understanding 18 / 48

  43. Hough Transform: Line Detection Hough Voting algorithm [Source: S. Seitz] Sanja Fidler CSC420: Intro to Image Understanding 19 / 48

Download Presentation
Download Policy: The content available on the website is offered to you 'AS IS' for your personal information and use only. It cannot be commercialized, licensed, or distributed on other websites without prior consent from the author. To download a presentation, simply click this link. If you encounter any difficulties during the download process, it's possible that the publisher has removed the file from their server.

Recommend


More recommend