trajectory-based ball detection and tracking with aid of homography in broadcast tennis video
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Trajectory-Based Ball Detection and Tracking with Aid of Homography in Broadcast Tennis Video. Xinguo Yu, Nianjuan Jiang, Ee Luang Ang. Visual Communications and Image Processing 2007 Proc. of SPIE-IS&T Electronic Imaging, SPIE Vol. 6508. Present by komod. Introduction. - PowerPoint PPT PresentationTRANSCRIPT
Trajectory-Based Ball Detection and Tracking with Aid of Homography
in Broadcast Tennis Video
Xinguo Yu, Nianjuan Jiang, Ee Luang Ang
Present by komod
Visual Communications and Image Processing 2007
Proc. of SPIE-IS&T Electronic Imaging, SPIE Vol. 6508
Introduction
• The ball is the most important object in tennis (and in many kind of sports)
• Very challenging problem– Camera motion– presence of many ball-like objects– small size and the high speed of the ball– Object-indistinguishable
Introduction
• Method– Trajectory-based
• the ball is the “most active” object in tennis video• previous work : A Trajectory-based ball detection
and tracking algorithm in broadcast tennis video, Proc. of ICIP
– Homography• Goal
– find projection locations of the ball on the ground
– find landing positions
Introduction
Introduction
Feature Point Extraction• Court Segmentation
– Find the court color range and paint all the pixels in this range with a single color
– find the lines separating the audience from the playing field
• detecting the change pattern of color for each row and column of the image
– paint the audience area in the court color.
Feature Point Extraction
• Straight Line Detection– gridding Hough transform
• Court Fitting – Detect the net and use it as reference– find the intersection of lines
Homography Acquisition
• Standard Frame– whose lookat is the cluster center of all
lookats of all the frames in the considered clip
– The lookat of frame is a point in the real world that corresponds to the center of the frame
Homography Acquisition
• Disparity Measure of Two Court Images– For i = 1 to 9
• Measure Function– Let Cstd be the court in the standard frame and Ctrn
denote the transformed court from the segmented court in frame F
– For given H and F
Homography Acquisition
• Initial Matrix– transforms an image point X' (x1', y2', 1) to a
point X (x1, y2, 1) in another image– X = HX‘
• Tuning of Homography– The homograph matrix computed based on
feature points
– A small hough space enclosing it
Homography Acquisition
• Tuning procedure
• Frame transform
Ball Location In Hitting Frame
• Hitting frame detection– Find the sound emitted by the racket
hitting• M. Xu et al, Creating audio keywords for
event detection in soccer video, In Proc. of ICME
• Hitting racket detection– Maybe player tracking
Ball Candidate Detection
• Object segmentation from standard frame• Four sieve are used for non-ball object removal
– Court Sieve Θ1
• filter out audience area• filter out court lines
– Ball Size Sieve Θ2
• filter out the objects out of the ball-size range• homography from ground model to standard frame• use a range of allowable ball sizes (estimate error)
– Ball Color Sieve Θ3
• filter out the objects with too few ball color pixels
– Shape Sieve Θ4
• filter out objects out of the range of width-to-height ratio• 2.5 is suggested in previous paper
– Each sieve is a Boolean function on domain Ο(F)
– The set of remaining objects is C(F)• C(F) = {o : o ∈O(F), Θi(o)=1 for i = 1 to 4}
• Candidate Classification– Three features are use
• Size, color, and distance from other objects
– The ball-candidates are classified into 3 Categories
Ball Candidate Detection
Candidate Trajectory Generation
• No detail explanation in this paper– X. Yu et al, Trajectory-based ball detection and
tracking of broadcast soccer video, IEEE Transactions on Multimedia, issue 6, 2006.
• Candidate Feature Plots (CFPs)– CFP-y– CFP-l
• The algorithm is actually works on the CFP-l which are 3-D plots
Candidate Trajectory Generation
Trajectory Processing
• Trajectory Confidence Index– Let T be a candidate trajectory
– and λ1,λ2,…,λm, be all properties of trajectory T
– confidence index Ω(T)
Trajectory Processing
• Trajectory Discrimination
Trajectory Processing
• Ball Projection Location– y = an3 + bn2 + cn + d.
• Ball Land Detection– form a ball position function against
frame number i, y = f(i)– find the maximum of f '(i) between each
pair of hittings
Experimental Results
• 5 clips
• extracted from mpeg2 704x576
• average time for acquiring ball candidates
• ALGnew for a frame is 86.15s on a P4/1.7Ghz PC with 512MB RAM
• ALGold is 19.21s
Experimental Results
BPL
Experimental Results
Experimental Results
• average discrepancy of all detected balls from the groundtruth
previous result
Experimental Results• frames with inserted 3D projected virtual content
• Homography in home surveillance video
Conclusion and Future Works
• The previous algorithm mainly alleviated the challenges raised by causes besides camera motion
• The algorithm presented in this paper additionally counteracts the challenges brought to us by the camera motion
• The contributions of this paper are two-fold– it develops a procedure to robustly acquire an accurate
homograph matrix of each frame– it forms an improved version of ball detection and tracking
algorithm• Two future works
– evolve the algorithm into an end-to-end system for ball detection and tracking of broadcast tennis video
– analyze the tactics of players and winning-patterns, and hence produce rich indexing of broadcast tennis video by making use of the ball position
Any Question?
Thank You
Experimental Results
• 7 segments, total 120 s, mpeg1 video, Men’s Final of FRENCH OPEN 2003
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