Tuan Q. Pham, Matthew Duggan. Bidirectional bias correction for Gradient-Based Shift Estimation. In Proceedings of the International Conference on Image Processing, ICIP 2008, October 12-15, 2008, San Diego, California, USA. pages 829-832, IEEE, 2008. [doi]
This paper characterizes the bias of a Gradient-Based Shift Estimator (GBSE) and proposes a novel scheme to correct for the bias. The bias of GBSE comes from an inaccurate estimate of the image gradient energy, which is due to noise, aliasing and built-in low-pass filtering. For subpixel shift, the bias is linearly proportional to the true shift. The linear bias factor can be blindly estimated using two or more subpixel shift estimates of the same image pair, each estimate is performed on a slightly shifted version of the second image. Compared to the original GBSE, the new method reduces the bias by half at the same time improving the precision.