Fig. 1. Principle diagram of photogrammetry

Fig. 2. Schematic diagram of the digital image correlation method

Fig. 3. Large deformation or cracks of the thin film materials

Fig. 4. Sequential frame-by-frame benchmark matching method

Fig. 5. Experimental device and software

Fig. 6. Measurement process

Fig. 7. Q235 steel specimen

Fig. 8. Comparison with two different methods

Fig. 9. Pliable composite film and speckle spray

Fig. 10. Camera calibration

Fig. 11. Surface strain distribution in different states

Fig. 12. Strain-state diagram of flexible composite film

Fig. 13. Determination of cut-off position

Fig. 14. Necking area of specimen

Fig. 15. Limit strain fitting

Fig. 16. Limit strain curve of pliable composite film

Fig. 17. Crack position is too biased or multiple cracks

Fig. 18. Limit strain fitting