Announcements
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Project 2 due today |
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Project 3 out today |
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demo session at the end of
class |
Photometric Stereo
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Readings |
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Forsyth and Ponce, section 5.4 |
Diffuse reflection
Shape from shading
Photometric stereo
Solving the equations
More than three lights
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Get better results by using
more lights |
Color images
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The case of RGB images |
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get three sets of equations,
one per color channel: |
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Simple solution: first solve for N using one channel |
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Then substitute known N into
above equations to get kd s: |
Computing light source
directions
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Trick: place a chrome sphere in the scene |
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the location of the highlight
tells you where the light source is |
Recall the rule for
specular reflection
Computing the light
source direction
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Can compute N by studying this
figure |
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Hints: |
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use this equation: |
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can measure c, h, and r in the
image |
Depth from normals
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Get a similar equation for V2 |
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Each normal gives us two linear
constraints on z |
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compute z values by solving a
matrix equation (project 3) |
Project 3
Limitations
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Big problems |
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doesn’t work for shiny things,
semi-translucent things |
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shadows, inter-reflections |
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Smaller problems |
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camera and lights have to be
distant |
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calibration requirements |
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measure light source
directions, intensities |
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camera response function |
Trick for handling
shadows
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Weight each equation by the
pixel brightness: |