Date: 2013/05/27 Instructor : Prof. Wang , Sheng- Jyh Student: Hung, Fei -Fan

RECOGNIZING HUMAN-OBJECT INTERACTION IN STILL IMAGE BY MODELING THE MUTUAL CONTEXT OF OBJECTS AND HUMAN POSESDate: 2013/05/27Instructor: Prof. Wang, Sheng-Jyh Student: Hung, Fei-Fan

Yao, B., and Fei-fei, L. IEEE Transactions on PAMI(2012)

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Outline• Introduction

• Intuition and goal• Model Representation• Model Learning

• Obtaining Atomic Poses• Training Detectors and Classifiers• Estimating Model Parameters

• Model Inference• Experimental Results• Conclusion

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Why using context in computer vision?

• simple image vs. human activities

~3-4%

with context

without context

With mutual context:

Without context:

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Challenges in Human Pose Estimation

• Human pose estimation is challenging

• Object detection facilitate human pose estimation

Difficult part appearance

Self-occlusion

Image region looks like a body part

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Challenges in Object Detection• Object detection is challenging

• human pose estimation facilitate object detection

Small, low-resolution, partially occluded

Image region similar to detection target

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The Goal• To build a mutual context model in Human-Object

Interaction(HOI) activities

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Tennis ball

Croquet mallet

Volleyball

Tennis racket

O:

Model representation• Modeling the mutual context of object and human poses

A:

Croquet shot

Volleyball smash

Tennis forehand

H:

P: body parts,

, M:num of bounding box

More than one atomic pose H in A

Body parts

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• : co-occurrence compatibility between A,O,H• : spatial relationship between O,H• : modeling the image evidence with detectors or classifiers

Model representation

H

A

P1 P2 PL

O1 O2

activity

Human poseobjects

11𝝓1: Co-occurrence context• co-occurrence between all A,O,H

• : strength of co-occurrence interaction

between

: indicator function: total number of atomic poses : total number of objects : total number of activity classes

H

A

P1 P2 PL

O1 O2

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• Spatial relationship between all O and different H

• : weight of • : a sparse binary vector • shows relative location• of w.r.t.

𝝓2: Spatial context

H

A

P1 P2 PL

O1 O2

:

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• Model O in the image I using object detection score

• For all object O• : vector of score of detecting • : weight of

• Between Om and Om’

• : binary feature vector• : weight of and

𝝓3: Modeling objects

H

A

P1 P2 PL

O1 O2

14𝝓4: Modeling human pose• Model atomic pose that H belongs to and likelihood

• : Gaussian likelihood function• : vector of score of detecting body part in

H

A

P1 P2 PL

O1 O2

15𝝓5: Modeling activity• Model HOI activity by training activity classifier

• : -dim output of one-versus-all (OVA) discriminative classifier taking image as features

• : feature weight of

H

A

P1 P2 PL

O1 O2

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Model Properties• Spatial context between O and H

• Object detection and human pose estimation facilitate each other • Ignore the objects and body parts that are unreliable

• Flexible to extend to large scale datasets and other activities• Jointly model can share all objects and atomic poses

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Model Learning

Assign human pose to atomic pose

Training detectors and classifiers

Estimate parameters by Maximum Likelihood

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• Using clustering to obtain atomic poses

• Normalize the annotations

• Finding missing part• Using the nearest visible neighbor

• Obtain a set of atomic poses• Hierarchical clustering with maximum linkage measure :

Obtaining Atomic Poses




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Training Detectors and Classifiers• : Object detector in • : Human body part detector in

• : Overall activity classifier in




deformable part model

Spatial pyramid matching (SPM)SIFT + 3 level image pyramid

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Estimating Model Parameters• Estimate by using ML approach

with zero-mean Gaussian priorAssign human pose to atomic pose



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Learning result

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Model Inference

Initialize with learned results

New image

Update human body parts

Update object detection results

Update A and H labels

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Initialization

Initialize Activity classification

Object detectionHuman pose estimation

New image

Initialize with learned results

A: SPM classificationO: object detectionH: pictorial structure model

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Update model inference• Marginal distribution of human pose:

• Using mixture of Gaussian to refine the prior of body part




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Update model inference

• Greedy forward search method :• Initial and no object in bounding box• Select • Label box as • update

• Stop when <0




O,H

O,A,H O,I

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Update model inference• Enumerate possible A and H label

• Optimize




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Experimental Results (Sports Dataset)

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Experimental Results (Sports Dataset)

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Experimental Results (Sports Dataset)• Activity classification

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Experimental results (PPMI Dataset)

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Experimental results (PPMI Dataset)

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Conclusion• Mutual context can significantly improve the performance

in difficult visual recognition problems

• The joint model can share all the information

• Annotate all the human body parts and objects in training images

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Reference• Yao, B., and Fei-fei, L. “Recognizing Human-Object Interactions in

Still Images by Modeling the Mutual Context of Objects and Human Poses,” IEEE Transactions on Pattern Analysis and Machine Intelligence (2012)

• B. Yao and L. Fei-Fei, “Modeling Mutual Context of Object and Human Pose in Human-Object Interaction Activities,” Proc. IEEE Conf. Computer Vision and Pattern Recognition, 2010

• B. Sapp, A. Toshev, and B. Taskar, “Cascade Models for Articulated Pose Estimation,” Proc. European Conf. Computer Vision, 2010.

• S. Lazebnik, C. Schmid, and J. Ponce, “Beyond Bags of Features: Spatial Pyramid Matching for Recognizing Natural Scene Categories,” Proc. IEEE CS Conf. Computer Vision and Pattern Recognition, 2006.

• http://en.wikipedia.org/wiki/Hierarchical_clustering

Date: 2013/05/27 Instructor : Prof. Wang , Sheng- Jyh Student: Hung, Fei -Fan

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