: let user set separate linear and angular covariance values.
: apply appropriate rotations from frame_pose
Support binning (maybe just cv::resize)
Don't adjust K, P for ROI, set CameraInfo.roi fields instead
D parameter order is k1, k2, t1, t2, k3
: don't bother if there are no subscribers
: publish to ros, thumbnails and rect image in the Update call?