1 Mean shift and feature selection ECE 738 course project Zhaozheng Yin Spring 2005 Note: Figures...
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Transcript of 1 Mean shift and feature selection ECE 738 course project Zhaozheng Yin Spring 2005 Note: Figures...
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Mean shift and feature selection
ECE 738 course project
Zhaozheng YinSpring 2005
Note: Figures and ideas are copyrighted by original authors
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Outline
Detecting, tracking and recognizing moving
objects in video sequences is a hot topic.
• Mean shift algorithm---target localization
• Feature selection---target representation
• Experiment demos
• Conclusion and future work
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Mean shift: (1)history
Y. Cheng. “Mean Shift, Mode Seeking, and Clustering” PAMI 1995
D. Comaniciu, P Meer. “Robust analysis of feature spaces: color image segmentation” CVPR 1997
GR Bradski. “Computer vision face tracking for use in a perceptual user interface”. Intel Technology Jounal 1998.
D Comaniciu, V Ramesh, P Meer. “Real-time tracking of non-rigid objects using mean shift”. CVPR 2000 Best paper award and patent filed.
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Mean shift: (2)Idea
• Mean shift algorithm climbs the gradient of a probability distribution to find the nearest domain mode (peak)
@R. Collins CVPR 2003 @Comaniciu PAMI 2003
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Mean shift: (3)Comments
Instead of exhaustive search in the window, the gradient information provided by the mean shift is used to reduce the time cost
Much better than moving the search window pixel by pixel and scanning row by row
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Mean shift: (4)feature selection comes up…
• Given a likelihood image, locate the optimal location of the tracked object
• The likelihood image is generated by computing, at each pixel, the probability that the pixel belongs to the object based on the distribution of the feature
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Feature selection: (1)Introduction
• Feature description approaches– Statistical descriptor– Structure descriptor– Spectral descriptor
e.g. intensity, color, texture, appearance, shape, motion, depth and so on.
@Bradski Intel Technology Journal 98’
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Feature selection: (2) histogram
• Color histogram is widely used as object feature
@Bradski Intel Technology Journal 98’
Red: 1D cross section of an subsampled color probability distribution of a image
White: search window
Blue: mean shift point
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Feature selection: (3) comments
• Foreground and background appearance changes every frame, so the object features need to update
• Color tracking affected by colored lighting, dim illumination or too much illumination
• More object information should be used to increase the tracker robustness
@Bradski Intel Technology Journal 98’
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Experiment demos
Non-rigid shape change lighting change on object
Object with non-identical color similar color with background