Matrix and Tensor Tools for Computer Vision

Matrix and Tensor Tools
FOR COMPUTER VISION
ANDREWS C. SOBRAL
ANDREWSSOBRAL@GMAIL.COM
PH.D. STUDENT, COMPUTER VISION
LAB. L3I –UNIV. DE LA ROCHELLE, FRANCE

Principal Component Analysis(PCA)

Principal Component Analysis
PCA is a statistical procedure that uses orthogonal transformation to convert a set of observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components.
Dimensionality reduction
Variants: Multilinear PCA, ICA, LDA, Kernel PCA, Nonlinear PCA, ....
http://www.nlpca.org/pca_principal_component_analysis.html

Principal Component Analysishttp://store.elsevier.com/Introduction-to-Pattern-Recognition-A-Matlab-Approach/Sergios-Theodoridis/isbn-9780123744869/

SingularValue Decomposition(SVD)

Singular Value Decomposition
Formally, the singular value decomposition of anm×nreal or complex matrixMis a factorization of the form:
whereUis am×mreal or complexunitary matrix, Σ is anm×nrectangular diagonal matrixwith nonnegative real numbers on the diagonal, andV*(theconjugate transposeofV, or simply the transpose ofVifVis real) is ann×nreal or complexunitary matrix. The diagonal entries Σi,iof Σ are known as thesingular valuesofM. Themcolumns ofUand thencolumns ofVare called theleft-singular vectorsandright-singular vectorsofM, respectively.
generalization of eigenvalue decomposition
http://www.numtech.com/systems/

-3-2-10123-8-6-4-20246810X Z-3-2-10123-8-6-4-20246810Y ZZ 1020304051015202530354045-8-6-4-20246-4-2024-4-2024-10-50510ORIGINAL-4-2024-4-2024-10-50510Z =  1-4-2024-4-2024-10-50510Z =  1 +  2

Robust PCA
Sparse error matrix
Shttp://perception.csl.illinois.edu/matrix-rank/home.html
L
Underlyinglow-rank matrix
M
Matrix of corrupted observations

Robust PCAhttp://perception.csl.illinois.edu/matrix-rank/home.html

Robust PCA
OneeffectivewaytosolvePCPforthecaseoflargematricesistouseastandardaugmentedLagrangianmultipliermethod(ALM)(Bertsekas,1982).
and then minimizing it iteratively by setting
Where:
More information:
(Qiuand Vaswani, 2011), (Pope et al. 2011), (Rodríguez and Wohlberg, 2013)

Robust PCA
For more information see: (Lin et al., 2010)http://perception.csl.illinois.edu/matrix- rank/sample_code.html

Low-rank Representation (LRR)
Subspaceclustering
problem!

NON-NEGATIVE MATRIX FACTORIZATION (NMF)

Non-Negative Matrix Factorizations (NMF)
Inmanyapplications,dataisnon-negative,oftenduetophysicalconsiderations.
◦imagesaredescribedbypixelintensities;
◦textsarerepresentedbyvectorsofwordcounts;
Itisdesirabletoretainthenon-negativecharacteristicsoftheoriginaldata.

NMFprovidesanalternativeapproachtodecompositionthatassumesthatthedataandthecomponentsarenon- negative.
Forinterpretationpurposes,onecanthinkofimposingnon-negativityconstraintsonthefactorUsothatbasiselementsbelongtothesamespaceastheoriginaldata.
H>=0constraintsthebasiselementstobenonnegative.Moreover,inordertoforcethereconstructionofthebasiselementstobeadditive,onecanimposetheweightsWtobenonnegativeaswell,leadingtoapart-basedrepresentation.
W>=0imposesanadditivereconstruction.
References:
The Why and How of Nonnegative Matrix Factorization (Nicolas Gillis, 2014)
Nonnegative Matrix Factorization: Complexity, Algorithms and Applications (Nicolas Gillis, 2011),

Similartosparseandlow-rankmatrixdecompositions,e.g.RPCA,MahNMFrobustlyestimatesthelow-rankpartandthesparsepartofanon-negativematrixandthusperformseffectivelywhendataarecontaminatedbyoutliers.
https://sites.google.com/site/nmfsolvers/

Introduction to tensors
Tensorsaresimplymathematicalobjectsthatcanbeusedtodescribephysicalproperties.Infacttensorsaremerelyageneralizationofscalars,vectorsandmatrices;ascalarisazeroranktensor,avectorisafirstranktensorandamatrixisthesecondranktensor.

Subarrays, tubesand slicesof a 3rd order tensor.

Matricizationof a 3rd order tensor.

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Frontal Vertical Horizontal
Horizontal, vertical and frontal slices from a 3rd order tensor

Unfoldinga 3rd order tensor.

Tensor transposition
◦While there is only one way transpose a matrix there are an exponential number of ways to transpose an order-n tensor.
The 3rd ordercase:

Tensor decompositionmethods
Approaches:
◦Tucker / HOSVD
◦CANDECOMP-PARAFAC (CP)
◦Hierarchical Tucker (HT)
◦Tensor-Train decomposition (TT)
◦NTF (Non-negative Tensor Factorization)
◦NTD (Non-negative Tucker Decomposition)
◦NCP (Non-negative CP Decomposition)
References:
Tensor Decompositionsand Applications (Kolda and Bader, 2008)

Matrix and Tensor Tools for Computer Vision

CP
TheCPmodelisaspecialcaseoftheTuckermodel,wherethecoretensorissuperdiagonalandthenumberofcomponentsinthefactormatricesisthesame.
Solvingby ALS (alternatingleast squares) framework

Tensor decompositionmethods
Softwares
◦ThereareseveralMATLABtoolboxesavailablefordealingwithtensorsinCPandTuckerdecomposition,includingtheTensorToolbox,theN-waytoolbox,thePLSToolbox,andtheTensorlab.TheTT-ToolboxprovidesMATLABclassescoveringtensorsinTTandQTTdecomposition,aswellaslinearoperators.ThereisalsoaPythonimplementationoftheTT-toolboxcalledttpy.ThehtuckertoolboxprovidesaMATLABclassrepresentingatensorinHTdecomposition.

IncrementalSVD
Problem:
◦The matrix factorization step in SVD is computationally very expensive.
Solution:
◦Have a small pre-computed SVD model, and build upon this model incrementally using inexpensive techniques.
Businger(1970) and Bunch and Nielsen (1978) are the first authors who have proposed to update SVD sequentially with the arrival of more samples, i.e. appending/removing a row/column.
Subsequently various approaches have been proposed to update the SVD more efficiently and supporting new operations.
References:
Businger, P.A. Updatinga singularvalue decomposition. 1970
Bunch, J.R.; Nielsen, C.P. Updatingthe singularvalue decomposition. 1978

IncrementalSVD
F(t)
F(t+1)
F(t+2)
F(t+3)
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[U, S, V] = SVD( [ F(t), …, F(t+2) ] )
[U’, S’, V’] = iSVD([F(t+3), …, F(t+5)], [U,S,V])
F(t)
F(t+1)
F(t+2)
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[U, S, V] = SVD( [ F(t), …, F(t+1) ] )
[U’, S’, V’] = iSVD([F(t+1), …, F(t+3)], [U,S,V])
F(t)
F(t+1)
F(t+2)
F(t+3)
F(t+4)
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[U, S, V] = SVD( [ F(t), …, F(t+2) ] )
[U’, S’, V’] = iSVD([F(t+1), …, F(t+3)], [U,S,V])
F(t)
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[U, S, V] = SVD( [ F(t), …, F(t+1) ] )
[U’, S’, V’] = iSVD([F(t+1), …, F(t+3)], [U,S,V])

IncrementalSVD
Updating operation proposed by Sarwaret al. (2002):
References:
IncrementalSingularValue DecompositionAlgorithmsfor HighlyScalableRecommenderSystems(Sarwaret al., 2002)

IncrementalSVD
Operations proposed by Matthew Brand (2006):
References:
Fastlow-rankmodifications of the thinsingularvalue decomposition(Matthew Brand, 2006)

IncrementalSVD
Operations proposed by Melenchonand Martinez (2007):
References:
EfficientlyDowndating, Composingand SplittingSingularValue DecompositionsPreservingthe MeanInformation (Melenchónand Martínez, 2007)

IncrementalSVD algorithmsin Matlab
By Christopher Baker (Baker et al., 2012)
http://www.math.fsu.edu/~cbaker/IncPACK/
[Up,Sp,Vp] = SEQKL(A,k,t,[U S V])
Original version only supports the Updating operation
Added exponential forgetting factor to support Downdatingoperation
By David Ross (Ross et al., 2007)
http://www.cs.toronto.edu/~dross/ivt/
[U, D, mu, n] = sklm(data, U0, D0, mu0, n0, ff, K)
Supports mean-update, updatingand downdating
By David Wingate (Matthew Brand, 2006)
http://web.mit.edu/~wingated/www/index.html
[Up,Sp,Vp] = svd_update(U,S,V,A,B,force_orth)
update the SVD to be [X + A'*B]=Up*Sp*Vp' (a general matrix update).
[Up,Sp,Vp] = addblock_svd_update(U,S,V,A,force_orth)
update the SVD to be [X A] = Up*Sp*Vp' (add columns [ie, new data points])
size of Vpincreases
Amust be square matrix
[Up,Sp,Vp] = rank_one_svd_update(U,S,V,a,b,force_orth)
update the SVD to be [X + a*b'] = Up*Sp*Vp' (that is, a general rank-one update. This can be used to add columns, zero columns, change columns, recenterthe matrix, etc. ).

Incrementaltensor learning
Proposed by Sun et al. (2008)
◦Dynamic Tensor Analysis (DTA)
◦Streaming Tensor Analysis (STA)
◦Window-based Tensor Analysis (WTA)
References:
Incrementaltensor analysis: Theoryand applications (Sun et al, 2008)

Dynamic Tensor Analysis (DTA)
◦[T, C] = DTA(Xnew, R, C, alpha)
◦ApproximatelyupdatestensorPCA,accordingtonewtensorXnew,oldvariancematricesinCandhespecifieddimensionsinvectorR.TheinputXnewisatensor.TheresultreturnedinTisatuckertensorandCisthecellarrayofnewvariancematrices.

Streaming Tensor Analysis(STA)
◦[Tnew, S] = STA(Xnew, R, T, alpha, samplingPercent)
◦ApproximatelyupdatestensorPCA,accordingtonewtensorXnew,oldtuckerdecompositionTandhespecifieddimensionsinvectorR.TheinputXnewisatensororsptensor.TheresultreturnedinTisanewtuckertensorforXnew,Shastheenergyvectoralongeachmode.

Window-basedTensor Analysis(WTA)
◦[T, C] = WTA(Xnew, R, Xold, overlap, type, C)
◦Computewindow-basedtensordecomposition,accordingtoXnew(Xold)thenew(old)tensorwindow,overlapisthenumberofoverlappingtensorsandCvariancematricesexceptforthetimemodeofprevioustensorwindowandthespecifieddimensionsin vectorR,typecanbe'tucker'(default)or'parafac'.TheinputXnew(Xold)isatensor,sptensor,wherethefirstmodeistime.TheresultreturnedinTisatuckerorkruskaltensordependingontypeandCisthecellarrayofnewvariancematrices.

Proposed by Hu et al. (2011)
◦Incremental rank-(R1,R2,R3) tensor-based subspace learning
◦IRTSA-GBM (grayscale)
◦IRTSA-CBM (color)
References:
Incremental Tensor Subspace Learning and Its Applications to Foreground Segmentation and Tracking (Hu et al., 2011)
ApplyiSVD
SKLM
(Ross et al., 2007)

IRTSA architecture

Incrementalrank-(R1,R2,R3) tensor-basedsubspacelearning(Hu et al., 2011)
streaming
videodata
Background Modeling
ExponentialmovingaverageLK
J(t+1)
new sub-frame
tensor
Â(t)
sub-tensorAPPLY STANDARD RANK-R SVDUNFOLDING MODE-1,2,3
Set of N background images
For first N frames
low-rank
sub-tensor
model
B(t+1)
Newbackground
sub-frame
Â(t+1)
B(t+1)
drop last frameAPPLY INCREMENTAL SVD UNFOLDING MODE-1,2,3
updatedsub-tensor
foreground mask
For the nextframes
For the nextbackground sub-frame
Â(t+1)
updatedsub-tensorUPDATE
SKLM
(Ross et al., 2007)
{bg|fg} = P( J[t+1] | U[1], U[2], V[3] )
ForegroundDetection
Background Model
Initialization
Background Model
Maintenance

Incremental and Multi-feature Tensor Subspace Learning applied for Background Modeling and Subtraction
Performs feature extraction in the slidingblock
Build or update the tensor model
Store the last N frames in a slidingblock
streaming
videodata
Performs the iHoSVDto buildor update the low-rank model
foreground mask
Performs the ForegroundDetection
ℒ푡
low-rank
model
values
pixels
features
풯푡
removethe last frame fromslidingblock
add first frame coming from video stream
풜푡
…
(a)
(b)
(c)
(d)
(e)
More info: https://sites.google.com/site/ihosvd/
Highlights:
* Proposes an incremental low-rank HoSVD(iHOSVD) for background modeling and subtraction.
* A unified tensor model to represent the features extracted from the streaming video data.
Proposed by Sobralet al. (2014)

Matrix and Tensor Tools for Computer Vision

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Matrix and Tensor Tools for Computer Vision