Similarity Maps Using SSIM Index
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The document summarizes Michel Alves' 10-minute speech comparing two image quality assessment metrics: normalized cross-correlation (NCC) and structural similarity index (SSIM). It provides background on the metrics, including their mathematical formulas and properties. Various images are used to generate similarity maps using both metrics side-by-side for visual comparison. While NCC is simple and fast, SSIM better captures structural changes but has greater complexity and potential numerical instability. In conclusions, the document advises using an appropriate metric depending on application and reevaluating metrics in some cases.
![Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC
Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM
IntroductionIntroduction
How to measure the visual
similarity between images?
[Lima'15][Nasc'08]
...Using IQA Metrics...
Introduction
-1-1
+1+1
+1+1
-1-1
NCC
SSIM](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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Similarity Maps Using SSIM Index
- 1. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Ten Minute Speech :: Overview of Activities Developed in Disciplines and Guided Studies :: Laboratory Seminars and Meetings Federal University of Rio de Janeiro (UFRJ) :: Campus Cidade Universitária :: Rio de Janeiro :: Fundão Island :: COPPE/PESC/LCG :: March/2015 Using Similarity Maps in Visual Comparisons Michel Alves dos Santos Ten Minute Speech (March, 2015) Advisors: D.Sc. Ricardo Marroquim & Ph.D. Claúdio Esperança
- 2. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM IntroductionIntroduction How to measure the visual similarity between images? [Lima'15][Nasc'08] ...Using IQA Metrics... Introduction -1-1 +1+1 +1+1 -1-1 NCC SSIM
- 3. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM MetricsMetrics What metric should I use? MSE? PSNR? <<No!!! Avoid ambiguous metrics!>> Metrics Impulsive Noise, MSE = 225 "A Universal Image Quality Index", Wang & Bovik, 2002, IEEE Signal Processing Letters. Gaussian Bluring, MSE = 225 Contrast Stretching, MSE = 225 MAE?
- 4. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Today MetricsToday Metrics Today we have a hundred of metrics and several surveys! We will compare the performance of two... Each of these metrics have specific use... Metrics Metrics: NCC and SSIM...
- 5. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Range: NCC vs SSIMNCC vs SSIM Normalized Cross-Correlation: Structural Similarity Index: [Wang'04] In our comparison we will assemble similarity maps with these metrics... NCCxSSIM Range:
- 6. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM NCC – Normalized Cross-CorrelationNCC – Normalized Cross-Correlation covariance stdev mean mean stdev NCC
- 7. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM NCC – Normalized Cross-CorrelationNCC – Normalized Cross-Correlation Homogeneous Patches ...Numerical Instability... Suggestion: add a small ε in the denominator... NCC
- 8. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM SSIM – Structural Similarity IndexSSIM – Structural Similarity Index bits per pixel dynamic range of pixels suggestion suggestion SSIM
- 9. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM SSIM – Structural Similarity IndexSSIM – Structural Similarity Index Homogeneous Patches ...Constants Avoid Numerical Instability... SSIM
- 10. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Montage of MapMontage of Map 3x3 sub in 5x5 window 7 pixels in 5x5 window 9 pixels in 5x5 window Centered Window Directional Window 3x3 sub in 5x5 window TsujiTomita Nagao7 Nagao9 NagMod (compute a mean neighbors value around a central pixel) (target pixel value)(types of centralized neighborhood) Montage
- 11. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM ComparisonsComparisons Cartoon Lighting Color Harmonization Image-Based Reconstruction Comparisons
- 12. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM NCC Map[Lima'15][Nasc'08] *NCC Map with 3x3 window (centered neighborhood) Comparisons – Gingerbread - NCCComparisons – Gingerbread - NCC -1-1 +1+1 *Map obtained using YIQ luminance. Comparisons
- 13. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM SSIM Map[Lima'15][Nasc'08] *SSIM Map with 3x3 window (centered neighborhood) Comparisons – Gingerbread - SSIMComparisons – Gingerbread - SSIM -1-1 +1+1 *Map obtained using YIQ luminance. Comparisons
- 14. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM NCC Map SSIM Map Overlay -1-1 +1+1-1-1 +1+1 *NCC and SSIM Maps with 3x3 window (centered neighborhood) Comparisons – Gingerbread - MapsComparisons – Gingerbread - Maps -1-1 +1+1 Comparisons
- 15. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Purple Flower - NCCComparisons – Purple Flower - NCC NCC Map[Lima'15][Nasc'08] -1-1 +1+1 Observe the behavior of this index in homogeneous areas... *NCC Map with 3x3 window (centered neighborhood) *Map obtained using YIQ luminance. Comparisons
- 16. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Purple Flower - SSIMComparisons – Purple Flower - SSIM SSIM Map[Lima'15][Nasc'08] -1-1 +1+1 Observe the behavior of this index in homogeneous areas... *SSIM Map with 3x3 window (centered neighborhood) *Map obtained using YIQ luminance. Comparisons
- 17. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Purple Flower - MapsComparisons – Purple Flower - Maps Overlay[Lima'15][Nasc'08]NCCMap SSIMMap -1-1 +1+1 -1-1 +1+1 Comparisons
- 18. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Color HarmonizationComparisons – Color Harmonization -1-1 +1+1 -1-1 +1+1 InputHarmonized *Maps obtained using average luminance.[Color Harmonization Project'14] Comparisons NCCMapSSIMMap
- 19. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Color HarmonizationComparisons – Color Harmonization -1-1 +1+1 -1-1 +1+1 InputHarmonized *Maps obtained using YIQ luminance.[Color Harmonization Project'14] Comparisons NCCMapSSIMMap
- 20. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Image-Based ReconstructionComparisons – Image-Based Reconstruction -1-1 +1+1 -1-1 +1+1 NCCMapSSIMMap [Cout'15] PhotoRender *Maps obtained using YIQ luminance. *Dataset: Nana. Comparisons
- 21. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Image-Based ReconstructionComparisons – Image-Based Reconstruction -1-1 +1+1 -1-1 +1+1 NCCMapSSIMMap [Cout'15] PhotoRender *Back vision of the previous model. *Maps obtained using YIQ luminance. Comparisons
- 22. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Image-Based ReconstructionComparisons – Image-Based Reconstruction -1-1 +1+1 -1-1 +1+1 NCCMapSSIMMap [Cout'15] PhotoRender *Maps obtained using YIQ luminance. *Dataset: Buddha. Comparisons
- 23. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM Comparisons – Image-Based ReconstructionComparisons – Image-Based Reconstruction -1-1 +1+1 -1-1 +1+1 NCCMapSSIMMap [Cout'15] PhotoRender *Maps obtained using YIQ luminance. *Dataset: Gertrud. Comparisons
- 24. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Introduction ConclusionComparisonsMetrics MontageNCCxSSIM NCC SSIM ConclusionsConclusions NCC: SSIM: fast and simple... has numerical instability control... is not so simple... Advice: Use appropriate metric ever! excellent perception of structural change... not designed for images only... good perception of local variation... needs revaluation in pathological cases... presents numerical instability... Conclusion
- 25. Michel Alves – Laboratory of Computer Graphics (LCG) – Graduate Program in Systems Engineering and Computing – UFRJ/COPPE/PESC Ten Minute Speech :: Overview of Activities Developed in Disciplines and Guided Studies :: Laboratory Seminars and Meetings Federal University of Rio de Janeiro (UFRJ) :: Campus Cidade Universitária :: Rio de Janeiro :: Fundão Island :: COPPE/PESC/LCG :: March/2015 Thanks for your attention! References: [Nasc'08]: Representation and Ilumination of 2D Objects, 2008, Renata Nascimento et al. [Lima'15]: Local lighting cartoons method using tree regions, 2015, Ailton Lima. [Cout'15]: Per Vertex BRDF Acquisition, 2015, Daniel Coutinho. [CHPr'14]: Color Harmonization Project, 2014, Michel Alves. [Wang'04]: Image quality assessment: From error visibility to structural similarity, 2004, Zhou Wang et al. Michel Alves dos Santos