New interpolation methods for image-based sub-pixel displacement measurement based on correlation

This paper deals with image-based displacement measurement. The correlation method of displacement measurement computes the cross-correlation function from two images captured by a CCD camera. The shift level is then determined by the position of the maximum value of the cross-correlation function. If the cross-correlation function is computed directly from two pictures (without further modification), it is possible to determine the shift level only with resolution on whole pixels. If higher (sub-pixel) resolution is required, it is necessary to use interpolation. Interpolation of the input sequences requires high performance and expensive digital signal processors (DSP) or field programmable gate arrays (FPGA), therefore for a real-time application it is necessary to acquire the information about sub-pixel shift from a computed cross-correlation function. This paper describes two new real time methods which can obtain the information of the sub-pixel shift from the shape of the maximum of the cross-correlation function and its shape.