Add hystersis to minimize a bad interaction between the parameter clamp and moving / changing the size of the area being analyzed. In test images this was leading to slight excess of localizations whose x/y positions where on pixel boundaries (0.0, 1.0, 2.0, etc..). This problem appeared to be eliminated by adding the hystersis. However, there still seem to be some issues with biases when fitting the width (in 2d mode) which are reduced but not eliminated by adding hystersis.