The cross-conditional entropy, H, of the DRR image relative to the X-ray image is calculated and minimized by the optimization algorithm ^[1].

Parameters

Parameters for Conditional Entropy Metric * View Weighting This factor is used when evaluating a bone pose by comparing the DRR images to the X-ray images. It is the relative weight of the two views in the final image metric (0.0 = all view 1, 1.0 = all view 2). 0.5 means to weight each view equally. * Constant DRR Scaling Whether or not to scale the DRRs for each view by a constant value for all iterations of an optimization. If false, each DRR will be scaled so that its maximum value is equal to the DRR image scale value (//X-ray/DRR Settings// widget). If true, a single scale value will be calculated during the first iteration and be used to scale the DRRs in all subsequent iterations.

1. ↑ Wang F, Vemuri B, Rao M, Chen Y (2003). Cumulative residual entropy, a new measure of information & its application to image alignment. Proceedings of the Ninth IEEE International Conference on Computer Vision, October, 2003. DOI: 10.1109/ICCV.2003.1238395.