A Self-Organizing Approach to Background Subtraction for Visual Surveillance Applications

1. A Self-Organizing Approach to Background Subtraction for Visual Surveillance Applications Lucia Maddalena and Alfredo Petrosino, Senior Member, IEEE

2. Abstract • Detection of moving objects in video streams is the first relevant step of information extraction in many computer vision applications. • Detecting moving objects provides a focus of attention for recognition, classification, and activity analysis. • The proposed approach can handle scenes containing moving backgrounds, gradual illumination variations and camouflage, has no bootstrapping limitations.

3. Abstract • light changes: should adapt to gradual illumination changes. • moving background: should include changing background that is not of interest for visual surveillance, such as waving trees. • cast shadows: the background model should include the shadow cast by moving objects. • bootstrapping: the background model should be properly set up even in the absence of a complete and static (free of moving objects) training set at the beginning of the sequence. • camouflage: if their chromatic features are similar to those of the background model.

4. Modeling the background by Self-Organization A. Initial Background Model • In order to represent each weight vector, we choose the HSV color space. Such color space allows us to specify colors in a way that is close to human experience of colors. • Let (h, s, v) be the HSV components of the generic pixel (x, y) of the first sequence frame , and let be the model for pixel (x, y) . Each weight vector is a 3-D vector initialized as =(h, s, v)

5. Modeling the background by Self-Organization A. Initial Background Model • The complete set of weight vectors for all pixels of an image I with N rows and M columns is represented as a neuronal map A with n*N rows and n*M columns.

6. Modeling the background by Self-Organization B. Subtraction and Update of the Background Model • Each incoming pixel of the sequence frame is compared to the current pixel model C. If a best matching weight vector is found, it means that belongs to the background. • If isn’t found. is in the shadow cast by some object or not. (shadow information into the background model or foreground)

7. Modeling the background by Self-Organization B. Subtraction and Update of the Background Model

8. Modeling the background by Self-Organization

9. Modeling the background by Self-Organization • If the best match for current pixel is the weight vector , then the weight vectors that are updated according to (3) are weight vectors .

10. Modeling the background by Self-Organization

11. Modeling the background by Self-Organization • The basic idea is that a cast shadow darkens the background. where and indicate the hue, saturation, and value components of pixel .

12. Experimental Results 1) Sequence MSA: • Sequence MSA is consisting of 528 frames of 320*240 spatial resolution, acquired at a frequency of 30 fps.

13. Experimental Results 2) SequenceWalk1: • SequenceWalk1 is consisting of 611 frames of 384*288 spatial resolution, captured at a frequency of 25 fps.

14. Experimental Results

15. Experimental Results Accuracy Metrics: • For measuring accuracy we adopted different metrics, namely Recall (detection rate), Precision (positive prediction), , and Similarity.

16. Experimental Results

17. Experimental Results