Anodizing is literally controlled oxidization of aluminum by means of electrical current. Dyes are used during the process for color. Then you get into patterns, fades, blah-blah-blah. During my Semi-Pro paintball days I had a small rig setup in my garage for this type of work. It is "sort of like chrome is to steel" in that they both utilize electric current.
As for anodizing a bicycle frame, I do not recommend it. Unless you actually do use "hard anodizing" as you mentioned in your title. Hard anodizing is the name often associated with Type III (a military spec) anodizing. Not many "anodizers" are willing to this type, it can be quite involved.
I used to work in an anodising plant about 10 years ago. I haven't heard of pearl anodising. Hard anodising produces a thicker film upto 100um., cf normal anodising, typically 10-25um. It uses higher current densities and lower temp (0-5 degrees celcius), which produces a very hard coating. Not many anodisers do this because a larger rectifier capable ramping upto 100V and larger refrigeration plant are required.
Well the question stems from the new sugino 75 track rings in black. They used to be hard anodized, but the '07 ones are listed as pearl anodized. The whole ring is black (teeth as well), curious which 'color' would hold up better.