How to gain the ability to improve leather more than fine?

I just started and plan to make a stealthy Assassin. I created a full set of Scout Armor and improved all the armor parts to fine. To improve any further says I lack the current skill. I checked the Smithing skill tree and didn't see any perks that let me do that with leather. I just see things like steel, Orcish, Dwarven, Ebony and etc.