Non-Parametric Model for Background Subtraction
Ahmed Elgammal    David Harwood     Larry Davis
Abstract
In video surveillance systems, stationary cameras are typically used to monitor activities at outdoor or indoor sites. Since the cameras are stationary, the detection of moving objects can be achieved by comparing each new frame with a representation of the scene background. This process is called background subtraction and the scene representation is called the background model. Typically, background subtraction forms the first stage in automated visual surveillance systems. Results from background subtraction are used for further processing, such as tracking targets and understanding events.

Typically, in outdoor environments with moving trees and bushes, the background of the scene is not completely static. For example, one pixel can be the image of the sky at one frame, a tree leaf at another frame, a tree branch on a third frame and some mixture subsequently; in each situation the pixel will have a different intensity (color). This research focuses on how to construct a statistical representation of the scene background that supports sensitive detection of moving objects in the scene.

We introduced a novel background model and a background subtraction technique based on nonparametric statistical modeling of the pixel process. The model keeps a sample of intensity values for each pixel in the image and uses this sample to estimate the probability density function of the pixel intensity. The density function is estimated using kernel density estimation technique. Since this approach is quite general, the model can approximate any distribution for the pixel intensity without any assumptions about the underlying distribution shape.

The model can handle situations where the background of the scene is cluttered and not completely static but contains small motions that are due to moving tree branches and bushes. The model is updated continuously and therefore adapts to changes in the scene background. The approach runs in real-time and was successfully used for motion segmentation in many research projects in our labs.

 

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demo2_2.bmp (460854 bytes)
lehiOut2.bmp (460854 bytes)
rain_out_1.bmp (460854 bytes)
Details

 

See Results Video Clips

 

 

MPEG 

AVI 

Clip Description

Video Clip 1

Gray scale

MPEG - 4 MB

avi - 75 MB

two targets - back of AVW

Video Clip 2

Color

 MPEG - 5.3 MB

 avi - 80 MB

one target - back of AVW

Video Clip 3

Gray Scale

 MPEG - 4 MB

 avi - 76 MB

one walking and one biking - back of AVW

Video Clip 4

Gray Scale

 MPEG - 15 MB

 avi - 113 MB

Lehigh sequence

Video Clip 5

Color

MPEG - 1.6 MB

avi - 24.8 MB

Rain

Video Clip 6

Gray Scale

avi - 12.6 MB

Outdoor Camera Shaking

Video Clip 7

Color

 

avi - 84 MB

Indoor - Shadow Suppression

Publications
  • A. Elgammal, R. Duraiswami, D. Harwood and L. S. Davis “Background and Foreground Modeling using Non-parametric Kernel Density Estimation for Visual Surveillance”, Proceedings of the IEEE, July 2002. [PDF]
  • A. Elgammal, D. Harwood, L. S. Davis, “Non-parametric Model for Background Subtraction”, 6th European Conference on Computer Vision. Dublin, Ireland, June/July 2000. [PDF]
  • A. Elgammal, D. Harwood, L. S. Davis,  Non-parametric Model for Background Subtraction” IEEE ICCV99 Frame Rate Workshop. IEEE 7th International Conference on Computer Vision. Kerkyra, Greece, September 1999. [URL]