A combined hardware and software method for the projection center calibration of the diffraction pattern

The precise knowledge of the projection center (PC) coordinates is vital for diffraction techniques, especially for electron backscatter diffraction (EBSD) and transmission Kikuchi diffraction (TKD). Numerous techniques have been proposed for PC calibration, involving both hardware maneuver and algorithm developments. Hardware calibration is straightforward and less prone to systematic errors due to the imperfections of EBSD simulations, while software calibration generally displays small uncertainties yet possible biases. A novel method is proposed herein for PC calibration, associating a moving screen with image correlation, thus combining the strengths of both techniques. Multiple sets of diffraction patterns of the same sample area are acquired at different positions of the detector along its track. Exploiting the geometrical relationship between them through a dedicated integrated digital image correlation framework (IDIC-M) that also associates a simulated master pattern, the PC coordinates are obtained. A unique crystal orientation and varying PC values are sought relating the different diffraction patterns to fully benefit from their consistency. This hybrid method improves the precision of PC calibration by 74.0% and 21.8% as compared to pure (hardware) moving-screen method and (software) image correlation method, respectively. Besides, the present work further validates the gradient-based version of pattern correlation, free of perceivable systematic errors, and hence deemed efficient and reliable in EBSD practices.