Combining Multiple Representations on the TRECVID Search Task

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Combining Multiple Representations on the TRECVID Search Task. Arjen P. de Vries Thijs Westerveld Tzvetanka I. Ianeva. Introduction. Video Retrieval should take advantage of information from all available sources and modalities …but so far ASR best for almost any query

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### Combining Multiple Representations on the TRECVID Search Task

Arjen P. de Vries

Thijs Westerveld

Tzvetanka I. Ianeva

ICASSP, May 21 2004

Introduction
• Video Retrieval should take advantage of information from all available sources and modalities
• …but so far ASR best for almost any query
• LL11@TRECVID2003: Combining information sources
• Different models/modalities
• Multiple example images

ICASSP, May 21 2004

Calculate conditional probabilities of observing query samples given each model in the collectionRetrieval

Models

P(Q|M1)

Query

P(Q|M2)

P(Q|M3)

P(Q|M4)

ICASSP, May 21 2004

Indexing

Estimate a Gaussian Mixture Model from each keyframe (using EM)

Fixed number of components (C=8)

Feature vectors contain colour, texture, and position information from pixel blocks: <x,y,DCT>

Static Model

ICASSP, May 21 2004

Dynamic Model
• Indexing:
• GMM of multipleframes (N=29) around keyframe
• Feature vectors extended with time-stamp in [0,1]: <x,y,t,DCT>

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ICASSP, May 21 2004

Dynamic Model

ICASSP, May 21 2004

• More training data for models
• Reduced dependency upon selecting appropriate keyframe
• Some spatio-temporal aspects of shot are captured
• (Dis-)appearance of objects

ICASSP, May 21 2004

Experimental Set-up
• Build models for each shot
• Static, Dynamic, Language
• Build Queries from topics
• Construct simple keyword text query
• Select visual example
• Rescale and compress example images to match video size and quality

ICASSP, May 21 2004

Combining Modalities
• Independence assumption textual/visual
• P(Qt,Qv|Shot) = P(Qt|LM) * P(Qv|GMM)
• Combination works if both runs useful [CWI:TREC:2002]
• Dynamic run moreuseful than static run

ICASSP, May 21 2004

Dow Jones Topic (120)

ICASSP, May 21 2004

Dow Jones Topic (120)

ICASSP, May 21 2004

Arafat topic (103)

ICASSP, May 21 2004

Arafat Topic (103)

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Baseball topic (102)

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Merging Run Results

ICASSP, May 21 2004

Combining (conflicting) examples difficult [CWI:TREC:2002]

Single example  Miss relevant shots

Round-Robin Merging

Merging Run Results

Combined

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ICASSP, May 21 2004

Combining (conflicting) examples difficult [CWI:TREC:2002]

Single example  Miss relevant shots

Round-Robin Merging

Merging Run Results

Combined

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ICASSP, May 21 2004

Flames (112)

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Flames Topic (112)

ICASSP, May 21 2004

Conclusions
• For most topics, neither the static nor the dynamic visual model captures the user information need sufficiently…
• …averaged over 25 topics however, it is better to use both modalities than ASR only

Working hypothesis: Matching against both modalities gives robustness

ICASSP, May 21 2004

Conclusions
• Dynamic captures visual similarity better
• Thanks to spatio-temporal aspects?
• Experiments with full covariance matrix for <x,y,t>-dims
• Static model of KF is too fragile
• Dependency on single KF?
• To be tested by ranking max(all I-frames in shot)
• Not enough training data?

ICASSP, May 21 2004

Conclusions
• Visual aspects of an information need are best captured by using multiple examples
• Combining results for multiple (good) examples in round-robin fashion, each ranked on both modalities, gives near-best performance for almost all topics

ICASSP, May 21 2004