CS448f: Image Processing For Photography and Vision Blending and Pyramids.
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Transcript of CS448f: Image Processing For Photography and Vision Blending and Pyramids.
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- CS448f: Image Processing For Photography and Vision Blending and Pyramids
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- Blending Weve aligned our images. What now? Averaging Weighted averaging min/max/median
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- Noise reduction by Averaging
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- 2 Shots
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- 4 Shots
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- 8 Shots
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- 16 Shots
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- Noise Reduction by Averaging Were averaging random variables X and Y Both have variance S 2 Variance of X+Y = 2S 2 Std.Dev. of X+Y = sqrt(2). S Std.Dev of (X+Y)/2 = sqrt(2)/2. S Ie, every time we take twice as many photos, we reduce noise by sqrt(2)
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- Noise Reduction by Averaging Average 4 photos: noise gets reduced 2x Average 8 photos: noise gets reduced 3x Average 16 photos: noise gets reduced 4x
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- Noise Reduction by Median (demo)
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- Median v Average
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- Can we identify the bad pixels? Theyre unlike their neighbours Instead of averaging, weighted average where weight = similarity to neighbours
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- Weighted Average
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- Can we identify the bad pixels? Theyre unlike their neighbours Instead of averaging, weighted average where weight = similarity to neighbours Favors blurriness
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- Input
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- Other uses of Median Removing Transient Occluders (live demo) (Gates demo) (surf demo)
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- Panorama Stitching
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- Multiple Exposure Fusion
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- Focus Fusion
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- Pyramids Weve been breaking images into two terms for a variety of apps Coarse + Fine More generally we can break it into many terms: Very coarse + finer + finer... + finest.
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- Pyramids We can do this by blurring more and more:
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- Pyramids And then (optionally) taking differences --
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- Pyramids The coarse layers can be stored at low res. Gaussian Pyramid Laplacian Pyramid
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- Pyramids How much memory does this use?
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- Pyramid Uses: Sampling arbitrarily sized Gaussians Equalizing an image The different levels represent different frequency ranges We can scale each frequency level and recombine Blending multiple images
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- Pyramid Blending Key Insight: Coarse structure should blend very slowly between images (lots of feathering), while fine details should transition more quickly. More robust to tricky cases than plain old compositing
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- Inputs:
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- Compositing: Hard Mask
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- Compositing: Soft Mask
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- Multi-Band Blending
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- Exposure Fusion http://research.edm.uhasselt.be/~tmertens/papers/exposure_fusion_reduced.pdf