Introduction
Our 5-detector answers only "is it a 5?". But to read handwriting we need to know which digit it is — one of ten classes. That's multiclass classification (also called multinomial classification).
Everyday examples:
- Which animal is in this photo — cat, dog, rabbit or bird?
- Which language is this sentence written in?
- Which department should this customer email go to — billing, technical, sales?
Some algorithms can handle many classes directly. Others are binary only, but we can still use them for multiclass problems by combining several binary classifiers cleverly. This topic covers both.