Finally, the image-processing computer is a closed proprietary system that is not amenable to expansion or modifications. The software environment, LabView, allows for easy system modification and capabilities upgrade through its modular programming environment. The use of the digital camera, digital flatbed scanner, and the digital image import capabilities allows for analysis flexibility and increased displacement measurement resolution and resulting strain computation compared to the original system. System accuracy and resolution were determined using undeformed image sets subjected to controlled displacement levels. Displacement measurement accuracy is at the subpixel level and varies from 0.012 to 0.049 pixel using a high-contrast image and from 0.18 to 0.48 pixel using a mixed contrast image.
Measurement accuracy is a function of image quality and correlation parameter settings.
Maximum strain resolution using the high-contrast image varied from 49 to 133 me and was dependent on the correlation parameters and the maximum applied displacement. Errors in the correlation resulted in significant errors in the strain computation for the mixed-contrast image.