Color Stereo-Digital Image Correlation Method Using a Single 3CCD Color Camera

Single‐camera special stereo‐digital image correlation applied for accurate virtual fields method identification

“…Inspired by the two digital cameras‐based SS‐DIC and colour stereo‐DIC proposed in Zhang et al and Yu and Pan, a single 3CCD colour camera‐based SS‐DIC method is proposed (Figure ). The proposed SS‐DIC method composed of a 3CCD colour camera, a beam splitter prism located in front of the camera, a right‐angle prism placed before the beam splitter prism, a blue band‐pass filter attached to the right and front of the right‐angle prism, a red band‐pass filter attached to the left side of the beam splitter prism, two plane mirrors placed oblique to the left side of the beam splitter prism and right‐angle prism (with an oblique angle of 45°), and a plane mirror placed oblique to the right side of the right‐angle prism.…”

“…Afterwards, conventional stereo‐DIC is used to process these images to retrieve full‐field displacements and strains. More details about the separation and transformation of colour images and the calibration of the measuring system can be seen in Yu and Pan . Note that the region of interest (ROI), subset, and step sizes are selected in the left reference image (corresponding to red sub‐image).…”

“…In addition, the spectra of the three channels of the colour camera always inevitably result in colour crosstalk and coupling problem, which may result in an inaccurately separation of the collected images into red and blue colour images and introduce large errors in the correlation analysis . To overcome the colour coupling of the 3CCD colour camera, appropriate red and blue optical band‐pass filters with specified bandwidths should be employed; more details about this were presented in Yu and Pan …”

“…Rigid‐body translation tests of a flat plate were employed to examine the measurement accuracy of the proposed SS‐DIC using a single 3CCD colour camera; static and continuous tension tests of metal sheet were also employed to evaluate the performance of the proposed method for VFM identification. As shown in Figure a, the proposed SS‐DIC measuring system comprises a 3CCD colour camera (AT‐200CL, JAI Ltd., Japan), a 50‐mm optical lens, a beam splitter prisms (size: 50 mm × 50 mm × 50 mm), a right‐angle prism (50 mm on both right sides, height 50 mm), three planar mirrors, a blue (centre wavelength: 450 ± 2 nm, bandwidth: 30 nm) and a red (centre wave length: 630 ± 2 nm, bandwidth: 30 nm) optical band‐pass filters . In all these tests, the optical axis of the red optical path is parallel to the normal of the tested object surface and the optical axis of the blue optical path is inclined with respect to the specimen.…”

“…Moreover, it is difficult to realise accurate synchronisation of two ultra‐high speed cameras, which would be introducing considerable errors into the measured deformation. To reduce the cost and solve the problem of synchronisation of two cameras, single‐camera stereo‐DIC technique could be a great help. Among these techniques, the 3CCD camera‐based single‐camera stereo solution is expected to be the best candidate, because it can use the full frame of the CCD and has no cross talk between different colour channels …”