Horizon Map Capture

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Horizon Map Capture
H. Rushmeier, L. Balmelli, F. Bernardini
IBM TJ Watson Research Center
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OVERVIEW
I. Why Capture Horizon Maps? II. Capture
Processing Under Ideal Conditions III. Dealing
with Real World Data IV. Some Example Maps
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I. Why Capture Horizon Maps?
General Problem How do we capture and represent
existing objects ?
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I. Why Capture Horizon Maps?
Image maps used to represent object
detail Textures colors View Dependent
Textures changing colors Normals
relit details Surface Light Fields all
light from object
geometry
map
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I. Why Capture Horizon Maps?
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I. Why Capture Horizon Maps?
Goal Add captured cast shadows to normals maps
to represent more lighting effects Retain
ability to edit Store data in a form that is
fast to render
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I. Why Capture Horizon Maps?
Attached versus Cast Shadows
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I. Why Capture Horizon Maps?
Efficient representation of cast shadows Horizon
Maps (Max 88) hardware rendering (Sloan Cohen,
00, Kautz et al. 00)
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I. Why Capture Horizon Maps?
Simple Hardware Set Up
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I. Why Capture Horizon Maps?
Use Photometric Stereo to Compute Normals
Discard lightest and darkest values at each
pixel, solve
Li dot N,p Gi,p
L Light source direction, light i N Surface
normal at p Gi,p Gray scale, image I, pixel p
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I. Why Capture Horizon Maps?
Why not reconstruct surface from normals?
Discontinuities
Outliers
Results are by integration Effect of one bad
normal spreads across image
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I. Why Capture Horizon Maps?
Why not reconstruct surface from normals?
Error in L dot N smaller than error in height.
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I. Why Capture Horizon Maps?
Why not reconstruct surface from normals?
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I. Why Capture Horizon Maps?
shadows from reconstructed heights
captured
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II. Capture and Processing Under Ideal Conditions
1. Identify regions of cast shadow
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II. Capture and Processing Under Ideal Conditions
2. Identify height of ridge casting the shadow
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II. Capture and Processing Under Ideal Conditions
Ridge height exact for sharp bumps only
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II. Capture and Processing Under Ideal Conditions
Differentiate between bumps and grooves
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II. Capture and Processing Under Ideal Conditions
3. Compute horizon map for each pixel by marching
in light direction for each pixel until ridge
encountered
Compute angle q
ridge height h known
find distance from pixel to ridge in
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III. Dealing With Real World Data
Correcting for Finite Light Locations
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III. Dealing With Real World Data
Shadows arent really black analyze histograms
No spike at zero
shadow
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III. Dealing With Real World Data
Computing ridge locations Identifying types of
shadow edges
Jaggy edge can cause pixel parallel to be
misclassified as the end of the shadow
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III. Dealing With Real World Data
Computing Ridge locationsCombining, smoothing
data
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IV. Some Example Maps
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IV. Some Example Maps
captured
corrected for finite light
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IV. Some Example Maps
cast shadows
relit normals
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IV. Some Example Maps
horizon map
reconstructed image
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IV. Some Example Maps
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IV. Some Example Maps
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IV. Some Example Maps
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IV. Some Example Maps
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IV. Some Example Maps
Editing
layers
horizon map
colors
normals
ridges
Except for horizon maps, no pixel contains
lighting information from other pixels. New
horizon maps can be generated from edited ridges
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IV. Some Example Maps
copy
delete
cyan
blue
yellow
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IV. Some Example Maps
copy
delete
cyan
blue
yellow
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IV. Some Example Maps
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