1. Error Estimation in Digital Image Correlation Caused by Rigid Particles By Xiaodan (Danna) Ke

2.   Introduction   Simulation Process   Particle Extraction Algorithm   Particle Translation Algorithm   Preliminary Results   Future Work Content

3. Introduction to Digital Image Correlation (DIC) 1 Speckle patterns DIC is a non-contacting measurement method based on tracking speckle patterns on material surface before and after deformation to determine displacement and strain fields. Deformed state Reference state Force

4.   Working Principles: Calculate cross-correlation factor of subsets in both states   Center locations of subsets at deformed state will be correlated with those at reference state   Accuracy: ±0.02 pixels Introduction to Digital Image Correlation 2 Speckle patterns Deformed state Reference state Subset F (u,v)

5.   DIC assumes no difference bt. background and particles in pattern  Background and particles deform the same way   Problem caused by rigid particles  Error estimation is needed Introduction to Digital Image Correlation 3 Reference state Deformed state Flexible particlesRigid particles Stretch and translate Only translate !

6. Simulation Process 1  Rigid particles are introduced when applying DIC to biological materials  Simulation method is used to evaluate errors induced by rigid particles Mouse carotid vessel 0.5 mm

7.   Extract individual particles from reference image   Translate extracted particles according to pre-assigned displacement   Generate deformed image   Use Vic-2D (a given DIC package) to calculate displacement and strain   Compare result from DIC with pre- assigned displacement Simulation Process 2 Challenge part!

8.  Why to extract individual particles  Calculate centroid location and obtain accurate displacement assignment Particle Extraction Algorithm 2 20 294130 3451 16 85 105 1038 40 120 50 99 50 u x u1u1 Centroid

9.  Local neighborhood searching algorithm 1. Intensity threshold (60) 2. Extract continuous pixels for individual particles Particle Extraction Algorithm 3 24 32 32 33 41 39 36 29 23 30 38 41 58 74 68 52 34 27 34 44 66 100 124 116 75 38 29 39 44 75 130 158 141 89 46 31 38 40 64 96 124 118 70 38 29 31 39 41 55 62 65 45 32 25 Start

10.   Results Particle Extraction Algorithm 3 Original image Extracted particles

11.  Calculate centroid in subpixels  Assign displacement to particles  Translate particles  Integration  Deform background pixels  Fill holes based on interpolation  Generate deformed image Particle Translation Algorithm 1

12. Particle Translation Algorithm 2  Results Original image Pure rigid motion 10 pixel in width direction Pure 50% stretch in width direction

13. Particle Extraction Algorithm 3  Results Pure 50% stretch in width direction Rigid particles Flexible particles

14. Preliminary Results of Error Estimation DeformationGround truthDigital Image Correl. prediction Flexible particlesRigid particles Pure translation10.0 pixels, 0.0% 11.0 pixels, 0.0046% 10.8 pixels, 0.07% Pure stretch50.0%62.57%61.89% Trans.+stretch10.0 pixels, 50.0% 62.54%61.89% ? ? ? ?

15.  Debug codes  Separate clogged particles  Estimate errors for complicated deformation Future Work

16. Thank you!