Transcript 슬라이드 1
Webcam-synopsis:
Peeking Around the World
Young Ki Baik (CV Lab.)
2008. 4. 4 (Fri)
Webcam-Synopsis:
Peeking Around the World
References
Webcam Synopsis : Peeking Around the World
• Yael Pritch, Alex Rav-Acha, Avital Gutman Shmuel Peleg
• (ICCV 2007)
Non-Chronological Video Synopsis and Indexing
• Yael Pritch, Alex Rav-Acha, Shmuel Peleg (PAMI 2008)
Background Cut
• J. Sun, W. Zhang, X. Tang, and H. Shum (ECCV 2006)
Webcam-Synopsis:
Peeking Around the World
What is Video-Synopsis?
Video synopsis is compact video data reducing
spatio-temporal redundancy in input video.
Webcam-Synopsis:
Peeking Around the World
Demo (Final result)
Webcam-Synopsis:
Peeking Around the World
How can we make Video Synopsis?
Basic concept
• Detect activity tubes…
in input video I.
• Put activity tubes…
to the S…
considering relation between
- tubes and background.
- tube and other tubes.
Webcam-Synopsis:
Peeking Around the World
Synopsis
Properties of video synopsis S
• The video synopsis S should be substantially shorter
than the original video I.
• Maximum “activity” from the original video should
appear in the synopsis video.
• The dynamics of the objects should be preserved in the
synopsis video. (for example, regular fast-forward may
fail to preserve the dynamics of fast objects.)
• Visible seams and fragmented objects should be
avoided.
Webcam-Synopsis:
Peeking Around the World
OBJECT-BASED
SYNOPSIS
Webcam-Synopsis:
Peeking Around the World
Object-based synopsis construction
Online Phase
• This phase is done in real time during video capture.
• Preparing step for response phase.
Response Phase
• started with user query.
• This phase may take a few minutes, depending on
the activity in the time period of interest.
Webcam-Synopsis:
Peeking Around the World
Overall flow
Webcam-Synopsis:
Peeking Around the World
ONLINE PHASE
Webcam-Synopsis:
Peeking Around the World
Video Acquisition
Video Volume Data
t
y
I(x, y, t)
(x, y) :
t
:
: 3D Space Time Volume
Spatial coordinates of
the image
Frame index
x
Webcam-Synopsis:
Peeking Around the World
Background Video Construction
Temporal Median
t
Temporal Window
y
Sorting
by intensity
Selecting
x
median value
4 minutes
Webcam-Synopsis:
Peeking Around the World
Background Video Construction
t
t
y
y
x
x
I
B
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Using Background Cut (ECCV 2006)
• Using min-cut to get a smooth segmentation of
foreground objects.
• Only considering 2D image (not video).
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Extracting moving objects
• We have information for…
I(x, y, t) : 3D Space Time Volume
B(x, y, t) : 3D Space Time Volume for background
Current ~
I
: Current image
= I (x, y, current time)
B
: Current background image
= B (x, y, current time)
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Simplify Object detection problem to…
• Binary labeling f : Foreground = 1, Background = 0
• Obtaining the desirable labeling f …
→ with Gibbs energy function.
E( f ) E1 f r
rI
Color term
r ,s Neighbors
E2 f r , f s
Contrast term
r : target position of image
s : neighboring of target position (4 Neighbors)
: user defined weight
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Extracting moving objects
• Unary term (or color term)
E( f ) E1 f r
rI
r ,s Neighbors
d I r B r
E2 f r , f s
Color differences
between image and
background
Foreground energy
0
E1 1
k1 d
Background energy
d k1
otherwise
k1, k2 : user defined thresholds
E1 0 d - k1
0
d k2
k2 d k1
otherwise
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Using Background Cut (ECCV 2006)
• Using min-cut to get a smooth segmentation of
foreground objects.
• Only considering 2D image (not video).
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Extracting moving objects
• Binary term (or contrast term)
E( f ) E1 f r
rI
r ,s Neighbors
E2 f r , f s
E2 ( f r , f s ) f r f s Exp I r I s
In case of same labeling, energy is decreased.
In case of different labeling, energy defends on differences between neighboring
intensities.
: user defined weight
2
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Using min-cut algorithm…
-
Moving objects are extracted.
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Extracting moving objects
• Constructing a mask of all foreground pixels in space-time
volume.
• Applying a 3D morphological dilation on mask.
• Finally we can obtain activity tubes (or objects).
t
x
Example of tubes
Webcam-Synopsis:
Peeking Around the World
Moving Objects(tubes) Extraction
Object queue
• Obtained activity tubes are saved in queue.
End of online phase…
Webcam-Synopsis:
Peeking Around the World
RESPONSE PHASE
Webcam-Synopsis:
Peeking Around the World
Response phase
User query
When user query occurred, response phase are started.
• “I would like to watch in one minute a synopsis of the
video from this camera captured during the last hour.”
• “I would like to watch in five minutes a synopsis of
the last week.”…
Input
video
Synopsis
Webcam-Synopsis:
Peeking Around the World
Response phase
User query
• “I would like to watch in one minute a synopsis of the
video from this camera captured during the last hour.”
• “I would like to watch in five minutes a synopsis of the
last week.”…
Webcam-Synopsis:
Peeking Around the World
Creating time lapse background video
Time lapse background video (Bout)
• The background of the synopsis video
• It should represent the background changes over time.
• Day-night transitions, etc.
• It should represent the background of the activity tubes.
Background
Video
Sampling
uniformly
Time
lapse
BG
video
Webcam-Synopsis:
Peeking Around the World
Creating time lapse background video
Time lapse background video
• A temporal activity histogram Ha
• A uniform temporal histogram Ht
Webcam-Synopsis:
Peeking Around the World
Creating time lapse background video
Time lapse background video
• A temporal activity histogram Ha
• A uniform temporal histogram Ht
• Interpolating the two histograms
Hi = Ha + (1- λ)Ht
Background
Video (b)
Sampling
with Hi
Bout
Time
lapse
BG
video
Webcam-Synopsis:
Peeking Around the World
Selecting tubes and stitching
Definition
M b bˆ
M : temporal mapping (or time shift)
s e
t
t
b : tube with time segment b b , tb
ˆb : shifted tube with time segment tˆb tˆbs , tˆbe
Input
video
b
M
bˆ
Synopsis
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Energy for temporal mapping M
M b bˆ
E bˆ, bˆ E bˆ, bˆ
E M bQ Ea bˆ Es bˆ
b ,bQ
Q
, ,
t
c
: Queue
b
: target tube
: user selected weights
b
: other tube
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Graph
Node number = number of tube
Longest tube
tube
tube
Synopsis
tube
t
tube
label
label
Label = number of frame t
label
label
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Energy for temporal mapping M
• Unary term
bQ
E bˆ E bˆ
a
s
Synopsis
• Activity Cost
0
Ea bˆ =
ˆ I x, y , t B x , y , t
x,y,tb
tube region inside the S
tube region outside the S
Only pixel that were not entered into the synopsis are added to the activity
cost.
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Energy for temporal mapping M
• Unary term
bQ
E bˆ E bˆ
a
s
Synopsis
• Consistency with background
Es bˆ =
x,y bˆ ,ttbˆ tout
bˆ :
I bˆ x, y, t Bout x, y, t
border of the mapped activity tube
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Energy for temporal mapping M
• Binary term
b,bQ
Et bˆ, bˆ Ec bˆ, bˆ
• Collision Cost
Ec bˆ =
x,y,tˆt b ˆt b
I x, y, t B x, y, t bˆ I x, y, t B x, y, t bˆ
This expression give a low penalty to pixel
whose color is similar to the background…
Synopsis
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
Energy for temporal mapping M
• Binary term
b,bQ
Et bˆ, bˆ Ec bˆ, bˆ
• Temporal Consistency Cost
Et bˆ
Preserving the chronological order of events
Synopsis
Webcam-Synopsis:
Peeking Around the World
Select tubes and stitching
E(M) is minimized by Min-cut algorithm.
Stitching the synopsis video
• To make more reliable result…
→ The α–Poisson Image Blending
End of response phase…
Webcam-Synopsis:
Peeking Around the World
Conclusion
The method to creating a short video that is a synopsis
of and video stream has been presented.
Discussion
Contribution
• Found out new interesting application.
Can we find more contribution?
• Finding higher dimensional problem and Solving it.
• 3D volume animation, etc.