1 / 32

Recall: Gaussian smoothing/sampling

Recall: Gaussian smoothing/sampling. G 1/8. G 1/4. Gaussian 1/2. Solution: filter the image, then subsample Filter size should double for each ½ size reduction. Subsampling with Gaussian smoothing. Gaussian 1/2. G 1/4. G 1/8. Image Pyramids.

chesna
Download Presentation

Recall: Gaussian smoothing/sampling

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Recall: Gaussian smoothing/sampling G 1/8 G 1/4 Gaussian 1/2 • Solution: filter the image, then subsample • Filter size should double for each ½ size reduction.

  2. Subsampling with Gaussian smoothing Gaussian 1/2 G 1/4 G 1/8

  3. Image Pyramids • Known as a Gaussian Pyramid [Burt and Adelson, 1983] • In computer graphics, a mip map [Williams, 1983] • A precursor to wavelet transform

  4. Motivations

  5. Boundaries occur at different scales

  6. Texture: consists of multiple size scales Original • Learn the statistics of texture to recognize it • Synthesize texture based on learned model Synthesis

  7. Example: Image Blending

  8. A bar in the big images is a hair on the zebra’s nose; in smaller images, a stripe; in the smallest, the animal’s nose Figure from David Forsyth

  9. Gaussian pyramid construction filter mask • Repeat • Filter • Subsample • Until minimum resolution reached • can specify desired number of levels (e.g., 3-level pyramid) • The whole pyramid is only 4/3 the size of the original image!

  10. What does blurring take away? (recall) original

  11. What does blurring take away? (recall) smoothed (5x5 Gaussian)

  12. Boundaries! smoothed – original

  13. Band-pass filtering • Laplacian Pyramid (subband images) • Created from Gaussian pyramid by subtraction Gaussian Pyramid

  14. Gaussian Pyramid Computer Vision - A Modern Approach Set: Pyramids and Texture Slides by D.A. Forsyth

  15. Laplacian Pyramid Computer Vision - A Modern Approach Set: Pyramids and Texture Slides by D.A. Forsyth

  16. Gaussian Pyramid Laplacian Pyramid

  17. Applications • Compression • Set “most” coefficients in Laplacian pyramid to zero • Hide secret messages in images (eg, to check youtube plagiarism) • Image Restoration • Image Blending

  18. 0 1 0 1 0 1 Application: Pyramid Blending Left pyramid blend Right pyramid

  19. Image Blending Juxtaposition: too abrupt

  20. + = 1 0 1 0 Feathering Ileft Iright right left Encoding transparency I(x,y) = (aR, aG, aB, a) Iblend = left Ileft + right Iright

  21. 0 1 0 1 Affect of Window Size left right Blending window too big (compared to typical detail size)  transparency, “ghosts”

  22. 0 1 0 1 Affect of Window Size Blending window too small (compared to typical detail size)  transition too abrupt

  23. Problem and solution • Problem: Usually details of many different sizes! No single size of blending window works. • Solution Laplacian Pyramid separate images into levels. Each level has details of single size range. Blend corresponding levels for the two images using windows sized to match level

  24. 0 1 Good Window Size “Optimal” Window: smooth but not ghosted Burt and Adelson (83): Choose by pyramids…

  25. Pyramid Blending

  26. Pyramid Blending (Color)

  27. Laplacian Pyramid: Blending • General Approach: • Build Laplacian pyramids LA and LB from images A and B • Build a Gaussian pyramid GR from selected region R (black white corresponding images) • Form a combined pyramid LS from LA and LB using nodes of GR as weights: • LS(i,j) = GR(I,j,)*LA(I,j) + (1-GR(I,j))*LB(I,j) • Collapse the LS pyramid to get the final blended image

  28. laplacian level 4 laplacian level 2 laplacian level 0 left pyramid right pyramid blended pyramid

  29. Blending Regions

  30. Constructing the Laplacian Pyramid • Worked out in class. To be posted later.

More Related