Department of computer science and engineering Evaluation of Two Principal Image Quality Assessment...

department of computer scienceand engineering

Evaluation of Two Principal Image Quality Assessment Models

Martin Čadík, Pavel SlavíkCzech Technical University in Prague, Czech Republic

[email protected]

TU Wien, November 5, 2004

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Content

Image Quality Assessment Traditional error sensitivity approach, VDP Structure similarity approach, SSIM Traditional vs. Structural Approach Conclusion


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Image Quality Assessment

Assessing the quality of images– image compression– transmission of images

Subjective testing– the proper solution– expensive– time demanding– impossible embedding into algorithms


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Image Quality Assessment Models

RMSE is NOT sufficient

MODEL( , )= Detection

probability map


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Image Quality Assessment & Computer Graphics

Quality improvement Saving of resources Effective visualization of information etc.


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Error Sensitivity Based Approach

General framework

Visible Differences Predictor [Daly93] Perceptual Distortion Measure [Teo, Heeger 94] Visual Discrimination Model [Lubin 95] Gabor pyramid model [Taylor et al. 97] WVDP [Bradley 99]

P re -p ro c e s s in g

C S F F il te rin g

C h a n n e lD e c o m p o s itio n

E rro r N o rm a liz a tio na n d M a s k in g

R e fe re nc es ig n a l

Q u a lity /D is to r tio nM e a s u re

D is to r te ds ig n a l

E r ro rP o o lin g...

...


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Visible Differences Predictor

[Daly 93]

Threshold sensitivity Visual Masking

A m p lit.N o n lin .

C S F C o rte xT ra n s fo rm

M a s k in gF u n c t io n

A m p lit.N o n lin .

C S F C o rte xT ra n s fo rm

M a s k in gF u n c t io n

M u tua lM a s k in g

Psy

cho

me

tric

Fu

nctio

n

Pro

ba

bili

tyS

um

ma

tion

Vis

ual

iza

tion

of

Di ff

ere

nce

s

+

-

R e fe re nc eIm a ge

D is to r te dIm a ge


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Structural Similarity Based Approach

Main function of the HVS: to extract structural information

UQI [Wang 02] SSIM [Wang 04] Multidimensional Quality Measure Using SVD

[Shnayderman 04]


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Structural SIMilarity Index

[Wang 04]

Simple implementation Fast computation

LuminanceMeasurement

ContrastMeasurement

LuminanceComparison

Combination

StructureComparison

Contrast Comparison

Signal x

+

-

LuminanceMeasurement

ContrastMeasurement

Signal y

+

-

Sim ilarityMeasure

N

i ix1

2/1

1

2)(1

N

i xix x

)()(1 1 yi

N

i xixy yx


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Traditional vs. Structural – Subjective Testing

Independent subjective tests– 32 subjects– 30 uniformly compressed images (JPEG2000)– 30 ROI compressed images– difference expressed by ratings

Mean Opinion Scores


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Traditional vs. Structural – Objective Testing

Original (left) and ROI compressed (right) input images

SSIM probability map (left) and

VDP probability map (right)


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Traditional vs. Structural – Test Results

Quality predictions compared to subjective MOS for the SSIM (left) and for the VDP (right)

0

1

2

3

4

5

6

7

8

9

10

0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 1SSIM

Subj

ectiv

e M

OS

SSIM

Polynomial fit

0

1

2

3

4

5

6

7

8

9

10

30 40 50 60 70 80 90 100VDP

Subj

ectiv

e M

OS

VDP

Polynomial fit


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Traditional vs. Structural – Test Results (cont.)

Model CC CC-ROI SROCC-ROI

VDP 0.22 0.44 0.39

SSIM 0.72 0.51 0.45

Quality assessment performances of the SSIM and for the VDP models

CC – Pearson (parametric) correlation coefficient

SROCC – Spearman (non-parametric) correlation coefficient


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Conclusion

Independent comparison of two IQA approaches– VDP, SSIM– subjective data (uniform/ROI)

Results– SSIM better– SSIM faster to compute and easier to implement– both models perform badly in ROI tasks – SSIM can detect the ROI

=> SSIM significant alternative to thoroughly verified VDP


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Thank You for Your Attention

ANY QUESTIONS?

[email protected]

ACKNOWLEDGEMENTSThis project has been partly supported by the Ministry of Education, Youth and Sports of the Czech Republic under research program No. Y04/98: 212300014, and by the CTU in Prague - grant No. CTU0408813. Thanks to Radek Vaclavik and Martin Klima for their support during the subjective testing.

Department of computer science and engineering Evaluation of Two Principal Image Quality Assessment...

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