Like our human brain, we can first learn (train) the handwriting 0 and 1. After the traing (and test) accuray is good enough, we only need to study (traing) the hardwriting 2, Instead of cleaning all of learned memory, and relearn handwriting data 0, 1, and 2 at the same time.
Can CNN do the same thing? Can CNN learn something new, but keep the previous memory? If yes, the efficiency could be high. Right now, I have to give all of data at the same time, the efficiency is very very low.