Kretschmann Scalar for a Kerr-Newman Black Hole

I have derived the Kretschmann scalar for a general black hole of mass m, angular momentum per unit mass a, and electric charge Q. The Kretschmann scalar gives the amount of curvature of spacetime, as a function of position near (and within) a black hole. This allows one to display the ``appearance'' of the black hole itself, whether the black hole is merely of stellar mass or is a supermassive black hole at the center of an active galaxy. Schwarzschild black holes, rotating black holes, electrically charged black holes, and rotating electrically charged black holes are all illustrated. Rotating black holes are discovered to possess a negative curvature that is not analogous to that of a saddle.