Hello to everyone!!
this is my very first post here. I know this could be a old Post but in my case is still usefull, because i am in the same path (Newbie in arduino and with a broken maudio keyboard). I think there is two possible solutions for this matter. The first is the Very-Hard-ware way that is to invert all diodes (122 i think). The second one is the software way that consist in changing the values on the INPUT - OUTPUT array. Please forgive all misspelling. Me Tarzan. Best Regards.