Robert Collins
Penn State
Crowd Scene Analysis
• Using computer vision tools to look at
people in public places
• Real-time monitoring
– situation awareness
– notifications/alarms
• After-action review
– traffic analysis
VLPR 2012
Robert Collins
Penn State
Crowd Scene Analysis
Things we might want to know:
• How many people are there?
• How to track specific individuals?
• How to determine who is with whom?
Challenges:
Crowd scenes tend to have low resolution.
You rarely see individuals in isolation.
Indeed, there are frequent partial occlusions.
VLPR 2012
Robert Collins
Penn State
Crowd Counting
FAQ: How many people participated in ...
• Tahrir Square Protests
• Obama’s inaguration
• Occupy Wall Street
• Kumbh Mela
VLPR 2012
Robert Collins
Penn State
Jacob’s Method
• Herbert Jacobs, Berkeley, 1960s
• count = area * density
– 10 sqft/person – loose crowd (arm’s length from each other)
– 4.5 sqft/person – more dense
– 2.5 sqft/person – very dense (shoulder-to-shoulder)
• Problem: Pedestrians do not uniformly distribute
over a space, but clump together into groups or
clusters.
• Refinement: break area into a grid of ground patches
and estimate a different density in each small patch.
Accumulate these counts over whole area.
VLPR 2012
Robert Collins
Penn State
Example of Jacob’s Method
VLPR 2012
source http://www.popularmechanics.com/science/the-curious-science-of-counting-a-crowd
Robert Collins
Penn State
Computer Vision Could do Better!
Cavaet: nobody really wants accurate counts
e.g. organizers of the “Million Man March” in
Washington DC threatened to sue the
National Park Service for estimating that
only 400K people attended.
VLPR 2012
Robert Collins
Penn State
Vision-based Counting
• detection and tracking (light density)
• clustering feature trajectories that move
coherently (moderate density)
• treat crowd as a dynamic texture and
compute regression estimates based on
measured properties (heavy density)
VLPR 2012
Robert Collins
Penn State
Detecting and Counting Individuals
Ge and Collins, "Marked Point Processes for Crowd Counting," IEEE Computer Vision and
Pattern Recognition (CVPR'09), Miami, FL, June 2009, pp.2913-2920.
Good for low-resolution / wide-angle views.
Relies on foreground/background segmentation.
Not appropriate for very high crowd density or stationary people.
VLPR 2012