My regular readers may be wondering why the "Screen-Space Bump Maps" and "Partial Derivative Normal Maps" articles are missing. If you have been following them lately, you may have noticed they kept receiving numerous changes. After coming across a lot of new information both from reading, and my own experiments, I have decided to take them down for now. I plan to repost them soon with more accurate information, better example images, and hopefully not requiring further revision.
My apologies for the inconvenience.