shadow-free segmentation in still images using...
TRANSCRIPT
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SHADOW-FREE SEGMENTATION IN STILL IMAGES USING
LOCAL DENSITY MEASURE
Aleksandrs Ecins, Cornelia Fermüller
and Yiannis Aloimonos
University of Maryland Computer Vision Lab
June 23, 2014
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DENSITY MAP MOTIVATION
Input
Gra
ysca
le
Textons [Malik et al 2001]
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DENSITY MAP MOTIVATION
Input
Gra
ysca
le
Textons [Malik et al 2001]
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• Intuitively density measures how a function changes locally over multiple scales
• Define a measure function on the image over a radius
• Hypothesize that it varies as an exponential of the radius
• is the local density measure at pixel
µ(x, r) =X
ky−xkr
I(y)
IMAGE DENSITY MAP
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APPLICATION TO TEXTURE DESCRIPTION
Input
Gra
ysca
le
Textons [Malik et al 2001]
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APPLICATION TO TEXTURE DESCRIPTION
Input
Gra
ysca
le
Textons [Malik et al 2001]
Den
sity
map
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APPLICATION TO TEXTURE DESCRIPTION
Input
Gra
ysca
le
Textons [Malik et al 2001]
Den
sity
map
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0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 10
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
Recall
Pre
cis
ion
PR
Intensity (85.20%), AUC=0.890%
Density (89.00%), AUC=0.942%
LBP (85.40%), AUC=0.910%
intensity + texture
SHADOW BOUNDARY DETECTION
• Goal: given a boundary in an image recognize if it is a shadow boundary
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FIGURE GROUND SEGMENTATION AND SHADOWS
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FIGURE GROUND SEGMENTATION AND SHADOWS
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STEP 1: SEGMENT
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STEP 2: DETECT SHADOWS
0
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1
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STEP 3: ATTENUATE STRONG SHADOW EDGES
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STEP 4: OVERSEGMENT THE SEGMENTATION AREA
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STEP 5: ADD EDGES BETWEEN SEGMENTS
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STEP 6: SEGMENT AGAIN
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QUANTITATIVE EVALUATION
• Dataset of 53 outdoor images of objects affected by shadows
• Groundtruth segmentation and segmentation initialization for each image
• Compared 4 algorithms
Algorithm F-measure
Baseline 0.77±0.027
Intensity textons 0.81±0.036
LBP 0.82±0.039
Density textons 0.84±0.033
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EXAMPLES
Baseline Shadow-free Baseline Shadow-free
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Code available online at www.umiacs.umd.edu/~aecins/
THANKS FOR YOUR ATTENTION
Questions?
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FAILURE EXAMPLES
Baseline Shadow detection Shadow-free
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IMPORTANT PROPERTIES OF THE DENSITY MAP
Preserves textural features
Intensity Density
Invariant to local multiplicative changes
to intensity